Telescopic Anchoring and Supporting Elements










Telescopic Anchoring
and Supporting
Elements
129
Precision Fittings
The detachable anchoring and supporting elements for partial dentures are invariably
precision  ttings, such as spring ring, parallel, conical, and thread  ts (Fig 5-1). Arti cial
crowns are constructed to carry these  ttings. In principle, every replacement crown is
suitable as an anchoring element for extensive partial restorations—as a partial denture
abutment, as a double crown for removable partial dentures and dentures, as a carrier
for attachment parts, or as a crowned clasp tooth. When used in such forms, the restored
tooth is loaded more than a single crown within a closed dental arch. The physiologic
conditions remain intact, but stresses arise that can tip or twist the tooth in the socket or
pull it out of the socket.
A tting refers to two structural components that can be  tted into one another and
that have  tting surfaces with speci c differences in dimensions; in other words, matched
parts have the same nominal dimension with  xed tolerances. The  rst matched part,
known as the primary part (inner matched part), can have a positive or a negative geo-
metric shape. The second matched part, or secondary part (outer matched part), has a
negative or positive geometric shape that matches the primary part (Fig 5-2). (Use of
the term “female part,” referring to a negative recessed  t into which the positive raised
“male part” is inserted, is unclear in dental technology and leads to confusion.) In den-

130
Telescopic Anchoring and Supporting Elements
tal technology, a tting comprises a primary part
xed to the residual dentition and a secondary
part located on the denture.
The denture is exposed to forces from all di-
rections, which act on the abutment teeth via the
anchoring components. An elastic anchoring ele-
ment transfers forces to the periodontium of the
abutment tooth in such a way that, in addition to
the normal axial forces, tipping, twisting, and pull-
ing forces act on the tooth and load it nonphysio-
logically. In periodontally borne and mucosa-borne
dentures, elastic anchoring components pro duce
statically indeterminate systems that cannot be
calculated and are therefore always awed.
By means of mobile anchoring elements, main-
ly uncontrolled dynamic stresses are transferred
to the abutment tooth, which does not occur with
a rigid connector; rocking movements on a yield-
ing mucosal support can drag the abutment tooth
to and fro in its socket until it loosens and is lost.
The mucosal support will not withstand such dy-
namic stresses caused by a denture base.
The natural teeth are also exposed to forces
from all directions; they compensate for these
forces in a closed dental arch and convert them
into physiologic stresses. Elastic anchoring ele-
ments with one or more movement possibilities
load the abutment tooth and the edentulous parts
of the dental arch in an uncontrolled way to the
detriment of that tissue.
It is assumed that elastic or mobile connections
between the residual dentition and the prosthe-
sis reduce the loading for the abutment tooth.
An elastic connection, however, only alters the
loading direction. When a cantilever xed partial
denture is loaded perpendicular to the support
by masticatory pressure and sinks into the mu-
cosal support, a hinge or another elastic connec-
tion will convert the intrinsically axial load for the
abutment tooth into additional tensile stress in
the distal direction, thereby tipping the tooth. In
addition, extremely uneven loading of the muco-
sal support occurs, which is very pronounced dis-
tally and only minimal mesially, in the pressure
Fig 5-1 The usual precision ttings for
dental anchoring components are fabri-
cated by hand but are also available as
prefabricated auxiliary parts.
Parallel t Conical t
Springt
Thread t
Primary part (matrix)
Secondary part (patrix)
Fig 5-2 A parallel tting that connects
the residual dentition to a removable res-
toration has two structural parts that can
be inserted into each other where the
matching parts have the same nominal
dimensions. The positive geometric
structural parts are called patrices, and
the negative matched parts are known as
matrices. In dental technology, the pri-
mary matched part is located on the xed
tooth replacement (eg, a crown), and the
secondary structural part is located on
the removable prosthetic replacement.

131
Parallel Fitting
shadow under the joint. In the process, the mar-
ginal periodontium of the abutment tooth close
to the saddle can be crushed horizontally.
In a rigid connection (coupling), the vertical
masticatory pressure can also lead to tipping
of the abutment tooth, but most of the force is
transferred axially. This protects the mucosal
support in particular. If the abutment tooth is
joined to several remaining teeth by splinting, the
tipping is balanced by a rigid connection to the
denture; conversely, if the connection is elastic,
all the splinted teeth are pulled in a distal direc-
tion, not least to the detriment of the loaded mu-
cosa.
A rigid coupling between denture and residual
dentition can be achieved with telescopic compo-
nents in the form of parallel and conical ttings
(Fig 5-3). They should be preferred to elastic con-
nections (Fig 5-4).
Parallel Fitting
Parallel tting refers to two telescopic structural
components in which the tting surfaces run par-
allel throughout the entire insertion length—for
example, a cylindric drill hole with a xed diam-
eter and specic depth into which a shaft of the
same diameter is pushed. The shaft can easily
be pushed in if the drill hole is slightly bigger,
but it cannot be inserted, or can only be inserted
with great force, if the shaft is bigger by a simi-
lar amount. The accuracy of a parallel t can be
ascertained directly from the difference between
the diameter of the shaft and that of the drill hole
(Figs 5-5 to 5-7).
The quality of a technical t is measured by the
difference between the internal diameter of the
outer matched part and the external diameter of
the inner matched part. Depending on the differ-
ence in diameters, the following parallel ts can
be identied:
Press t exists if the shaft diameter (D
S
) is great-
er than the drill-hole diameter (D
DH
): D
DH
< D
S
Transition t exists if the drill-hole diameter and
shaft diameter are the same: D
DH
= D
S
Clearance t exists if the drill-hole diameter is
greater than the shaft diameter: D
DH
> D
S
Clearance (or play) denotes a positive difference
in size; that is, the drill hole is larger than the
shaft. Oversize denotes a negative difference in
size when the shaft is larger than the drill hole.
In mechanical engineering, parallel ttings are
produced by a costly process with computer-
controlled machine tools in which the dimensions
are set and controlled via photoelectric measur-
ing devices. The accuracy of these ts is in the re-
gion of ten-thousandths of millimeters. With den-
tal technology techniques, surfaces polished to a
Fig 5-3 Another precision tting in telescopic components is
a conical t, which can be used as a rigid anchoring element.
Conical ttings are produced by hand as conical (tapered)
crowns and industrially as conical attachments.
Fig 5-4 A resilient circumferential tting is mainly used as a
handmade cast clasp or as a prefabricated stud tting. The elas-
tic clasp arms are pushed over the widest circumference of the
tooth, engage in the undercuts, and perform a retentive func-
tion.

132
Telescopic Anchoring and Supporting Elements
high glaze, for instance, have a surface roughness
in the order of several thousandths of millimeters.
In mechanical engineering, parallel ttings are
generally applied to inseparable connections. In
dental technology, however, this t is produced
for separable connections with dimensional inac-
curacies within the range of a tenth of a millime-
ter. The practicability of the different t qualities
in dental technology will be analyzed individually:
Press t is not used in dental technology because
the matched parts can only be pushed on with
considerable force. Once the matched parts are
brought together, however, elastic deformation
(the outer part is widened, the inner part com-
pressed) will press the tting surfaces so rmly
against each other that they can only be disen-
gaged with great difculty. Even greater force is
needed to separate the parts than to join them to-
gether. The matched parts are wedged together,
the tting surfaces can fuse together, and an in-
separable connection can arise.
Transition t (or snug t) can only be used in
certain cases. Joining and separating the matched
parts is associated with considerable friction ef-
fects, depending on surface roughness. The parts
t together snugly as a good but incalculable ad-
hesive effect occurs throughout the tting surface.
With moderate resistance to static and dynamic
friction, a transition t would be highly suitable
for anchors in dental technology. However, the
friction effects when joining and separating the
parts quickly lead to wear of the tting surfaces so
that a clearance t without appreciable adhesion
results after prolonged use.
Clearance t (or loose t) is the preferred type of
t. Matched parts can easily be joined and sepa-
rated with slight resistance to static and dynamic
friction and without any signs of wear, even dur-
Clearance t
Drill-hole diameter (D
DH
) is larger
than the shaft diameter (D
S
)
Transition t
Diameters of the drill hole and shaft
are identical
Press t
Shaft diameter is larger than the
drill-hole diameter
D
S
D
DH
D
S
D
S
D
DH
D
DH
D
S
= D
DH
D
S
< D
DH
D
S
> D
DH
Fig 5-5 The accuracy of a parallel tting is indicated by the match between the dimensions of the shaft and the drill hole; based on
the dimensional conformance or difference between the diameters of the two matched parts, three types of t are described.
Fig 5-6 One measure of the quality of a parallel t is the size of the tting surfaces that touch each other in a specic design. In
ttings for dental technology purposes, this absolute contact area can differ considerably in attachments of the same structural
height and width. Furthermore, if the tting surface is interrupted by additional activatable components, the absolute contact area
will be further reduced, as shown here in a dovetail tting.

133
Error Analysis of Parallel Fittings
ing frequent use. Only slight, but calculable, ad-
hesive effects occur, which are supported by ad-
ditional anchors. The undeniable advantage lies
in the fact that the matched parts have a dened
path of insertion and end position. Except from
the path of insertion, forces cannot lift off the res-
toration because a clearance t also provides a
rigid connection between the residual dentition
and the denture.
The quality of t can be determined from the
size of the joining and separating forces, which in
turn depend on the following:
• The size of the clearance
• The absolute size of the contact surfaces
• The absolute parallelism of the tting surfaces
• The contact pressure of the tting surfaces
The surface roughness of the tting surfaces
(contact pressure and tting surface roughness
must be low to prevent abrasion)
Error Analysis of
Parallel Fittings
The practical value of parallel ttings is measured
by the extent to which they fulll the dened
functions of anchoring and supporting elements.
While securing the horizontal and vertical posi-
tion, dened adhesion and bracing of the residual
dentition are ensured by ts that have little clear-
ance (play) and absolute parallelism, that do not
have any abrasion, and whose matched parts are
not displaced. Clearance, parallelism, abrasion,
and displacement of the matched parts depend
on the technical process.
Size of clearance
In dental technology fabrication processes, the
size of clearance depends on several factors. The
primary part of the tting is milled; the secondary
part is carved out of wax over the primary part,
cast, and nished, during which the following
procedural and system errors can occur:
• Stresses during wax preparation
Expansion inaccuracies of the investment mate-
rial
Granulation of the investment material for sur-
face roughness
Casting errors, such as blowholes, inclusions,
and casting beads
• Casting temperature that is too high or too low
Surface treatment errors, such as airborne-
particle abrasion, glazing, corrective reduction,
and polishing
Surface roughness of
tting surfaces
Size of tting surfaces Parallelism of tting
surfaces
Size of clearance
Fig 5-7 Quality of t.

134
Telescopic Anchoring and Supporting Elements
Typical procedural and system errors have such
an effect during the fabrication of parallel ttings
that all types of t, such as clearance, transition,
and press t, occur by chance (Figs 5-8 and 5-9).
This is mainly attributable not to the dental techni-
cian’s shortcomings but to the special fabrication
methods involved in dental technology, which are
inadequate for such levels of accuracy.
Parallelism
A precise cylindric t is difcult to achieve by
dental technology fabrication methods because
procedural and system errors occur, giving rise
to different forms of t by chance. A true cylindric
t is an inverted cone that is opposite to the direc-
tion of withdrawal or a true cone.
Wax processing
errors
Casting errors
Airborne-particle abrading
with the wrong abrasive
Electrolytic
processing
Grinding and polishing
of tting surfaces
Fig 5-8 As a result of dental technology
processing methods, all three types of
t—cylindric t, conical t, and inverted
cone—can arise by chance when the aim
is to produce a parallel t.
Fig 5-9 Error-free fabrication of the secondary part is not possible with dental technology processing meth-
ods. Quality of t is inuenced by procedural and system errors, which can add up to an unacceptable total
error.

135
Error Analysis of Parallel Fittings
When the parallel surface is being milled, the
cutter is guided by hand. As a result, small differ-
ences in working pressure can cause a change in
the milled surface, and grooves or chatter marks
arise (Fig 5-10). If the part being worked is slightly
raised or tilted from the base, partially undercut
areas will be formed. If the bearings of the mill-
ing machine are worn out or if it is not possible to
achieve accurate parallel guidance of the milling
cutter, no parallel milled surface can be produced.
This kind of system error due to the tool and mill-
ing machine can easily be overlooked.
Abrasion of parallel ttings
When the matched parts are joined and separat-
ed, dynamic friction takes place throughout the
tting surface from the moment the rst move-
ment starts until the end position is reached. This
friction gives rise to abrasion, which is increased
by the following:
•The surfaces tting together more tightly; if
there is very little clearance, the surfaces slide
against each other under greater contact pres-
sure
•The increased surface roughness of the tting
surfaces
Even during normal use, a parallel tting will
change its shape due to abrasion. After a brief
wearing time, a transition t becomes a clearance
t, which calls into question the value of this t-
ting if no additional anchorage aids are provided.
Displacement of individual
matched parts
From model die to tooth preparation in the pa-
tient’s mouth, the matched parts can be displaced
in relation to each other. In accurate parallel t-
tings, even a positional difference of 0.2 mm is
problematic enough to jeopardize the success of
the whole piece of work. Possible causes of dis-
placement include the following:
Inaccuracies in impression-taking; after the try-
in, the primary parts are not placed in the correct
position in the combined impression
Individual primary parts are shifted on the mill-
ing model compared with the original model
Secondary parts have warped during the pro-
cessing steps performed
Secondary parts shift in the mouth during ce-
mentation because of the space required for the
cement
The primary part may also become tilted if both
matched parts are cemented in place together in
the prosthetic unit. On insertion, great pressure has
to be exerted, which can tilt the tooth preparation.
Insertion grooves on the prepared tooth may pro-
vide the simplest solution in this situation.
Working pressure too high;
the cutter bends
Tilting of the milling model;
undercut areas
Run-out errors during milling;
chatter marks
Fig 5-10 Precise parallelism
can be reliably achieved with
primary parts using dental
technology processing meth-
ods. Procedural errors can
occur, however, because the
cutter is guided by hand.

136
Telescopic Anchoring and Supporting Elements
Manually Fabricated
Attachment Fittings
The group of parallel ttings includes manually
milled attachment ttings because of their mode
of action and physical properties. These parallel
ttings make up the primary part, which is milled
in the replacement crown; the secondary part is
xed to the removable replacement. The three
classic forms of manually fabricated attachments—
ring or cylindric form, horseshoe form, and T-form
(Fig 5-11)—were described by Steiger (Zürich) in
1924.
The ring or cylindric form is an occlusally open
telescope that encircles the replacement crown
as a closed ring. To increase the static friction,
two channels can be milled approximally, into
which the matching pins engage. These pins may
comprise resilient wires and are activatable. To
brace against axial masticatory forces, a shoulder
around the neck prevents the cylindric tting from
slipping off. Transverse forces are absorbed by
this cylindric attachment, just like a closed tele-
scopic crown. An anchoring band clasp is a pos-
sible modication.
An anchoring band crown is the primary part
of this attachment structure in the form of a full
crown with circular parallel milling that has a
0.5-mm-wide cervical shoulder. The milled sur-
face is interrupted on one approximal surface and
has two parallel limiting channels. An anchoring
band clasp is a telescopic clasp that is open ap-
proximally on one side and placed onto the an-
choring band crown as the secondary part. It can
be activated to increase the static and dynamic
friction effects.
The horseshoe form encloses the replacement
crown as a semicircular milling into which the ac-
curately tting secondary part engages. To in-
crease adhesion, approximal channel and pin re-
tentions are milled. A bar connection running
occlusally and cervical shoulder millings help to
secure the vertical position. The pin, channel, and
shoulder millings enlarge the static friction sur-
face areas and brace the structure. Possible de-
signs are the channel-shoulder-pin attachment and
the encircling catch with shear distribution arm.
The channel-shoulder-pin milling is applied to
a veneered crown and runs over the approximal
and lingual surfaces. The semicircular tting sur-
face ends in a cervical shoulder; it has pin inlets
and parallel-milled channels that dene the sur-
face area as well as a channel running occlusally
(Fig 5-12). The approximal and occlusal channels
as well as the cervical shoulder offer the exur-
ally rigid frame for the semicircular secondary
part; the occlusal surface can be formed by the
secondary part. The pins, made of bend-resistant
wires, are soldered into the cast outer crown;
they are activatable spring pins that increase stat-
ic friction. The vertical pins counteract withdrawal
forces intraorally. A channel-shoulder milling is a
semicircular milling reduced by the pin inlets.
The encircling catch is a semicircular parallel
milling with a cervical shoulder on the lingual
surface of an abutment crown to which a pre-
Fig 5-11 Manually milled attachment ttings can be reduced to three basic forms. The cylindric form (as a ring telescope) and the
horseshoe form (as a channel-shoulder-pin attachment) are the most commonly used in manual fabrication.
T-form, used as a T-attachment in a
prefabricated version
Cylindric form, used as a ring tele-
scope or occlusally open telescope
Horseshoe form used as a half-ring
with channels and pin millings

137
Manually Fabricated Attachment Fittings
fabricated attachment is tted approximally. The
milled surface runs from the attachment over the
lingual surface to the opposing approximal sur-
face, which has a cylindric end groove that limits
the surface area. The milled surface and cylindric
milling run parallel to the attachment’s path of in-
sertion. The cylindric milling can be conical and
widened occlusally; this makes handling easier.
The shear distribution arm (balancing compo-
nent) is an open semicircular telescope with an
approximal stabilizer. The shear distribution arm
engages in the encircling catch, aids secure po-
sitioning during insertion, secures the horizontal
and vertical position, and supports the rigid cou-
pling of the prefabricated attachment (Figs 5-13
and 5-14). Encircling catches with shear distribu-
Occlusal shoulder
milling
Parallel vertical
channels
Guide channel
for spring pin
Parallel sliding
surface
Cervical shoulder
milling
Occlusal transverse
channel
Fig 5-12 The occlusal surface can
be formed by the subcrown in a
channel-shoulder-pin attachment or
be covered by the outer crown (as in
the illustration). If there is no cervical
shoulder milling, the occlusal surface
should be formed by the outer crown,
or a sturdy encircling occlusal shoul-
der should be milled.
Fig 5-13 An encircling catch with
shear distributor is used as a stabiliz-
ing element for prefabricated struc-
tural components and should rigidly
secure the vertical and horizontal
position for a removable restoration.
An encircling catch and shear distri-
bution arm run over the lingual sur-
faces of the abutment teeth; for po-
sitional stability, approximal stabiliz-
ing channels are milled parallel to the
prefabricated attachment.
Fig 5-14 The encircling catch for the
shear distribution arm is milled paral-
lel to the prefabricated attachment
and has approximal stabilization or
end channels. If the encircling catch
passes over two abutment teeth, the
stabilization channel can be prepared
as an interlock milling. The cervical
shoulder offers vertical positional
safeguarding, and the occlusal shoul-
der marks the upper end of the
milled surface.
Prefabricated
attachment
Interlock milling
Parallel milling
Cervical shoulder
Occlusal shoulder
Approximal stabilization
channel

138
Telescopic Anchoring and Supporting Elements
tors can also be combined with a resilient anchor-
ing component (stud anchor).
The T-form or T-attachment is sunk approximally
into the replacement crown as a hollow form. The
T-shaped secondary part is seated on the remov-
able replacement. The shape of a T-attachment
requires considerable loss of tooth substance
approximally, which may be available because
of a very pronounced cavity. The T-form is milled
by hand but also used in industrially fabricated
attachments. In principle, manually fabricated at-
tachment ttings have the same indications as
telescopic crowns. The advantage of semicircu-
lar channel-shoulder-pin attachments is that they
require a smaller space than telescopic crowns
because the vestibular portion of the anchoring
crown does not have to be double walled.
Encircling Catch with
Shear Distributor
The encircling catch is milled parallel into a full
crown, while the matching shear distributor on
a removable replacement is integrated as a sup-
porting element. An additional anchoring element
has to take on the anchoring function.
Encircling catches with shear distributors are
the most popular structural forms as stabilizing
elements for delicate prefabricated attachments.
They are also combined with stud anchors, such
as CEKA and ZL anchors (ZL Microdent); in this
combination, the encircling catches rigidly secure
the vertical and horizontal position, while the stud
anchors take on the retentive function. The shear
distribution arm can also be combined with a
clasp as a splinting element. The basic form of a
double-arm clasp with onlay has an active vestib-
ular retentive arm and a lingual shear distributor
as the guide arm.
Following is the fabrication process for an en-
circling catch with shear distributor: The tooth is
prepared to receive a veneered crown, and the
preparation margin is shaped with a pronounced
shoulder. The dental tissue usually has to be re-
moved more than normal (approximately 1.2 mm).
An insertion channel is required to avoid shifts in
the model-to-intraoral situation.
The veneered crown framework can be pre-
pared to receive an acrylic resin or ceramic ve-
neer. The primary crown can be veneered with
ceramic, which is not possible with a telescopic
crown because the ceramic might ake off in re-
sponse to dynamic stresses from the outer tele-
scope.
The milled surface of the encircling catch is let
into the framework and is characterized by cervi-
cal shoulder milling. The milling of the encircling
catch has a threefold function:
1. It provides static support.
2. The shoulder depth ensures the material thick-
ness of the shear distributor.
3. It aids stability to prevent bending open.
A 0.5-mm-wide metal bar is left between the
veneer and the milled surface to reinforce the
veneer material. The encircling catch must have
a minimum height of 2.5 mm, which means the
shape of the anterior teeth may appear bulky. The
milled surface ends approximally in the parallel
(or conical) end channel, which becomes effec-
tive in a lingual direction against transverse with-
drawal forces.
To brace against the half-ring being bent open
and food compaction, the transitions from the
milled surface to the occlusal parts of the crown
are chamfered or end in occlusal shoulder mill-
ing. The encircling catch is waxed up/milled di-
rectly into the replacement crown, invested, and
cast. During milling of the tting surfaces, it is im-
portant to ensure the following:
•Milled surfaces are completely parallel.
The milled surface and prefabricated attach-
ment lie parallel.
Both portions are parallel in their path of inser-
tion.
• A milling model with milling base is prepared.
The shear distributor is waxed up together with
the denture framework. It fully covers the milled
tting surfaces and shoulder millings and com-
pletes the anatomical shape of the tooth. Its ma-
terial thickness is at least 0.5 mm, and the transi-
tions overlap slightly so that they can be rened.
Manually prefabricated structures place high
demands on craftsmanship and have wide t tol-

139
Telescopic Crowns
erances (Fig 5-15). If manually fabricated parallel
ttings are combined with prefabricated parallel
attachments, the differing t tolerances have an
unbalanced effect: The smaller t tolerance of the
prefabricated components produces a rmer seat-
ing; the prefabricated components have to absorb
the bulk of the stresses and are overloaded.
Error analysis of the encircling
catch
Poor parallelism: If the tting surfaces follow a
positive conical course, there is no dynamic fric-
tion; static friction depends on the slope of the
milled surfaces. If the tting surfaces are nega-
tively conical and undercut, the matched parts
cannot be joined (Fig 5-16).
Fitting surface is lower than 2.5 mm and the ab-
solute contact surface of the tting is too small:
This height does not provide stable anchorage
against tilting, twisting, or transfer of mastica-
tory forces; the area of static friction is also too
small (Fig 5-17).
No cervical shoulder and channels are too long:
Without a cervical shoulder milling, the vertical
position is jeopardized.
No occlusal shoulder but a sharp edge at the
margin of the milled surface: As a result, food
is easily compacted between the tting surfaces
(Fig 5-18).
Telescopic Crowns
Telescopic crowns are double crowns in which
the inner crown is cemented onto the tooth prep-
aration and the outer crown is coupled with a re-
movable tooth replacement. The tting surfaces
of the telescopic components can be worked as
parallel or conical ts. A telescopic crown, based
on the principle of a parallel t, comprises two
structural parts where the inner telescope (pri-
mary part) has at least two plane-parallel surfaces
facing each other and is completely enclosed by
the outer telescope (secondary part), which has
the anatomical tooth shape (Fig 5-19).
The inner telescope is fabricated by the milling
process and has plane-parallel outer surfaces.
The parallel surfaces lying opposite each other
approximally are usually sufcient for retention,
while the vestibular and lingual surfaces can fol-
low a conical course. The parallel surfaces must
be slightly rough for static friction effects. The
surfaces polished during dental laboratory work-
ing achieve just the right level of roughness. The
inner telescope is cemented onto the tooth prepa-
ration, which has an insertion channel for a de-
ned path of insertion.
When telescopic crowns are combined in a unit,
all of the telescopic surfaces must be parallel with
the path of insertion. The slightest deviations will
cause stresses. The inner telescope is at occlus-
H
Fig 5-15 In the case of man-
ually milled encircling catch-
es, which are associated with
prefabricated attachments, end
channels, and occlusal and
cervical shoulders, the follow-
ing errors occur (see Figs 5-16
to 5-18).
Fig 5-16 The tting surfaces
do not run parallel. If the tting
surfaces and channels are
negatively conical and under-
cut, the encircling catch and
shear distributor cannot be
joined together.
Fig 5-18 If there are no oc-
clusal and cervical shoulders,
the shear distributor ends in
sharp edges and the vertical
position is not secured; food
can be trapped between the
tting surfaces.
Fig 5-17 The height (H) of
the parallel tting surface is
smaller than 2.5 mm, and the
absolute contact surface of
the tting is too small; this
height is inadequate to ensure
positional stability.

140
Telescopic Anchoring and Supporting Elements
ally and has chamfered transitions to the milled
surfaces for ease of positioning during insertion.
The outer telescope is removable and has an
anatomical shape as a full-cast crown, veneered
crown, or occlusally open ring telescope and as a
telescopic band clasp (anchor band clasp), which
is supported on a circular shoulder on the inner
telescope (Fig 5-20). The outer telescope con-
tacts the parallel surfaces of the inner telescope
evenly throughout the retentive surface from ini-
tial placement to the stop. The telescopic parts
adhere by means of static and dynamic friction
effects; in addition, resilient elements or locking
devices may be used.
Indications for telescopic crowns
Telescopic crowns are used for removable den-
tures and removable partial prostheses. The par-
allel guided t offers a xed path of insertion and
a precisely rigid connection between the denture
and the residual dentition in a dened end posi-
tion. Telescopic units on several abutments pro-
vide excellent bracing of the residual dentition by
means of secondary splinting. The hygiene con-
ditions are particularly favorable with telescopic
crowns.
A double-walled crown demands more space
and requires greater loss of tooth substance dur-
ing preparation than normal replacement crowns
(Fig 5-21). Fabrication of a telescopic crown in-
volves considerably more work and hence is more
prone to error. Additional retentions incorporated
into the double crown require further space and
involve a more time-consuming technique that is
also prone to error.
Additional retentive elements for telescopic
crowns are mainly prefabricated components in
the form of activatable resilient and passive lock-
able components. They are elements for primary
and subsequent assembly that compensate for
inadequate adhesion and provide positional sta-
bilization of the matched parts.
Activatable resilient elements are prefabri-
cated systems that are typically integrated into
the outer matched part. The resilient element of
the outer crown snaps into a groove on the inner
crown and holds the matched parts by a gripping
Fig 5-19 Telescopic crowns are one form of parallel t. These
double crowns have an inner crown as the inner matched part
and an outer crown as the outer matched part. Telescopic
crowns are constructed so that at least two opposing external
surfaces of the inner crown run parallel. The outer crown has an
anatomical shape, and its inner wall is adapted to the inner
crown. The cervical crown margin is formed by the inner crown,
and the outer crown ends about 2 mm above the cervical mar-
gin. A cervical shoulder can be prepared on the inner crown, or
the outer crown has a tapered margin that is technically dif-
cult to produce and is usually unstable.
Fig 5-20 The occlusally open ring telescope is a special form
of telescopic crown. The telescopic part is a ring that is sup-
ported by a cervical shoulder in the inner telescope or by an
occlusal shoulder. The advantage of an occlusal shoulder on a
ring telescope is that no food collects between the matched
parts because the gap between them is horizontally directed.

141
Telescopic Crowns
effect (Fig 5-22). Numerous intracoronal retentive
components are available from various manufac-
turers; their spring elements are activatable and
replaceable (eg, Pressomatic [Romagnoli], Ipso-
clip [Guglielmetti; Fig 5-23], snap attachment, leaf
springs). Activatable components can be over-
stretched so that the periodontium is overloaded
when the telescope is withdrawn. Excessively
large clearance ttings cannot be stabilized with
these retentive components.
Components subsequently mounted for worn
matched parts are mainly rubberlike nubs that are
stuck into the outer crown. An angled depression
is milled into the outer telescope, and the rub-
ber nub is set in place so that a slight elevation
is formed on the tting surface and rubs on the
inner telescope.
Therefore, the requirements of telescopes are
the following:
• Easy to join and separate the matched parts
• Dened end position as a rigid connection
• Retention in resting position by static friction
• Abrasion-resistant t
• Delicate periodontally hygienic shape
Fig 5-21 A double-walled telescopic crown requires more
space than a normal-walled crown, which is why the tooth has
to undergo more extensive corrective reduction. Relatively
clumsy forms of outer telescope often result, however, be-
cause the parallel walls of the inner telescope do not support
the anatomical tooth shape. If only the approximal surfaces are
placed parallel, relatively delicate shaping of the vestibular sur-
face is possible.
Fig 5-22 An active anchorage aid in the form of a spring bolt is
housed in the outer telescope, which engages in a groove in
the inner crown in the resting position. A notch occlusally on
the inner telescope allows the spring bolt to be securely joined.
Component cap
Coil spring
Spring bolt
Component sleeve
Fig 5-23 The parts of the additional spring bolt an-
chor, here the Ipsoclip, are delicately constructed
so that they can be housed in the outer wall of the
secondary part. The spring bolt and coil spring are
replaceable.

142
Telescopic Anchoring and Supporting Elements
Conical Fittings
Conical crowns (after K. H. Körber) are manually
fabricated ttings in the form of telescopic double
crowns. The primary part has the positive shape
of a cone and is referred to as the inner cone or
inner crown; the secondary part is known as the
outer cone or outer crown and has an anatomical
tooth shape.
The cone is truncated and ts into an analogous
hollow cone, where the external surfaces of the
truncated cone are parallel to the internal surfac-
es of the hollow cone (Fig 5-24). In engineering,
a cone is dened by the height of the truncated
cone, over which the diameter changes by 1 mm
(Fig 5-25). The occlusal diameter of the primary
part of a conical crown is smaller than the diam-
eter in the cervical area.
The surfaces of a cone can be extended as far
as the original cone. The angle of the cone lies in
the apex of the cone. Halving this angle by the
central axis of the cone gives the angle of taper.
L
D
1
D
2
1 mm
Fig 5-24 A cone means a truncated cone that has side walls
sloping toward each other. A conical crown is a double crown
in which the inner crown displays the positive shape of a cone.
The tting surfaces of the double crown run parallel. A conical
tting is a separable join.
Fig 5-25 The cone is a truncated cone that changes diameter
by 1 mm over a specic height; this is the degree of taper of
the cone.
Fig 5-26 The slope of the side walls of a cone can be deter-
mined by the angle (α) to which a cone can be extended. The
angle of taper is half the cone angle (
α
/2). The taper angle indi-
cates the sloping of the side walls to the perpendicular. The
taper angle can be measured with a parallelometer. The angle
between the parallelometer rod and the cone wall gives the
angle of taper.
Fig 5-27 The tting surfaces of the conical crown come in
contact in the end position, and static friction arises. If the
outer cone is exposed to contact pressure F
A
, a ank force that
is vertical on the tting surfaces occurs at the surfaces and is
referred to as normal force F
N
. The magnitude of static friction
forces depends on the taper angle.
F
A
F
N
F
N

143
Conical Fittings
The angle of taper can be measured between
a parallelometer pin and the surface of the cone
(Fig 5-26). Therefore, the taper angle is dened as
the machining angle between the outer surface
of the cone and the parallelometer axis. In dental
technology, this taper angle is used to describe
the conical shape because the adhesive force of
the conical t can be specied with this angle.
The central axis of a cone lies parallel to the path
of insertion. The taper angle can be measured on
the basis of this path of insertion. In some cases,
the central axes of individual cones of a combina-
tion of abutments differ from the path of inser-
tion; one cone surface runs parallel to the path
of insertion, and the other cone surfaces are at a
positive angle to the path of insertion. This occurs
if abutment teeth are excessively tilted toward
each other.
The adhesive force of a cone does not arise un-
til the inner and outer crown touch in the resting
position. In a parallel t, dynamic friction occurs
from initial contact between the tting surfaces
until the matched parts are fully pushed inside
each other. If a cone is placed in a matching hol-
low cone, adhesion ensues when the plane sur-
faces of the two parts come into contact in the
end position.
Dynamic friction and abrasion do not occur in
a conical tting because the tting surfaces only
touch when the end position of the structure is
reached; these surfaces do not slide against each
other in contact. If a telescopic conical tting is
joined together, the cone surfaces do not rest
loosely but press against each other; thus, more
pressure is applied to the outer part. The inner
cone is pushed into the outer crown like a wedge,
whereby the outer crown is subject to slight elas-
tic deformation. The contact surfaces press rmly
together and static friction arises (Fig 5-27).
The physical principle of the adhesive force,
which depends on the contact force due to inser-
tion and masticatory pressure as well as on the
taper angle, can be explained by a wedge (Fig
5-28): If differently pointed wedges are driven into
a block of wood with the same force, a pointed
wedge will penetrate deeply and remain rmly in
position, a blunt wedge will have difculty pene-
trating the wood and can easily be removed, and
an even blunter wedge will not penetrate but will
repeatedly pop out.
The relationship between adhesive force and ta-
per angle can be determined by calculations and
experimental tests and can be graphically repre-
sented: The degrees are plotted on the horizontal
Fig 5-28 Comparison with a wedge
shows that the size of the taper angle
has a direct inuence on the adhesive
force of the cone: The smaller the taper
angle, the steeper the wedge, the larger
the anks, or the larger the normal forces
on the sides of the cone. If the taper or
wedge angle is larger, the ank forces
decrease and may reach the point where
the wedge or the cone comes off. This
happens because the slope forces be-
come greater than the static friction
forces.

144
Telescopic Anchoring and Supporting Elements
line (abscissa or x-axis) and the corresponding
adhesion values on the vertical line (ordinate or
y-axis). A small taper angle produces high adhe-
sive force, whereas a large taper angle has little
or no adhesive force (Fig 5-29).
In relation to adhesive force and taper angle,
Körber identies three types of cone (Figs 5-30
and 5-31):
Adhesive cone (adhesive anchor) with a taper
angle of 5.5 degrees (cone angle of 11 degrees)
Normal cone (normal anchor) with a taper angle
of 6 degrees (cone angle of 12 degrees)
Support cone (support anchor) with a taper an-
gle of 6.5 degrees (cone angle of 13 degrees)
Groups of conical crowns can be fabricated in
which crowns with different taper angles between
5.5 and 6.5 degrees produce different adhesive
forces:
Fig 5-29 The adhesive force of a cone depends on the angle
of taper. According to Körber, the mean values for adhesive
force can be dened for three angles of taper of function-related
cones: A 5.5-degree angle of taper produces a retentive anchor
with approximately 10 N of adhesive force; a 6-degree angle of
taper produces a normal anchor with approximately 6 N of ad-
hesive force; and a 6.5-degree angle of taper produces a sup-
porting anchor with approximately 5 N of adhesive force.
Fig 5-30 The most favorable taper angle for dental technology
constructions is 6 degrees, which is equivalent to a cone angle
of 12 degrees. If, in the case of tilted teeth within a group of
tapered crowns, the cone axis does not coincide with the tooth
axis, this difference can still be tolerated within a range of up
to 12 degrees. The chosen path of insertion is the axis, which
is used as the reference for the taper angle. If an angle of 8
degrees is chosen on one side and an angle of 4 degrees is
selected on the opposite side, this gives a cone angle of 12
degrees.
Fig 5-31 To give the inner crown an evenly thin wall thickness,
the taper angle of the different sides of a crown can vary. The
only decisive factor is that the total of the opposing angles re-
sults in the desired cone angle. If a cone angle of 12 degrees is
chosen, the total of the opposing taper angles must result in
exactly this number of degrees. For a normal adhesive cone, 12
degrees is appropriate. If the cone adheres very strongly, a
cone angle of less than 12 degrees must be selected.
Path of insertion

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Telescopic Anchoring and Supporting Elements129Precision FittingsThe detachable anchoring and supporting elements for partial dentures are invariably precision  ttings, such as spring ring, parallel, conical, and thread  ts (Fig 5-1). Arti cial crowns are constructed to carry these  ttings. In principle, every replacement crown is suitable as an anchoring element for extensive partial restorations—as a partial denture abutment, as a double crown for removable partial dentures and dentures, as a carrier for attachment parts, or as a crowned clasp tooth. When used in such forms, the restored tooth is loaded more than a single crown within a closed dental arch. The physiologic conditions remain intact, but stresses arise that can tip or twist the tooth in the socket or pull it out of the socket.A  tting refers to two structural components that can be  tted into one another and that have  tting surfaces with speci c differences in dimensions; in other words, matched parts have the same nominal dimension with  xed tolerances. The  rst matched part, known as the primary part (inner matched part), can have a positive or a negative geo-metric shape. The second matched part, or secondary part (outer matched part), has a negative or positive geometric shape that matches the primary part (Fig 5-2). (Use of the term “female part,” referring to a negative recessed  t into which the positive raised “male part” is inserted, is unclear in dental technology and leads to confusion.) In den- 130Telescopic Anchoring and Supporting Elementstal technology, a tting comprises a primary part xed to the residual dentition and a secondary part located on the denture.The denture is exposed to forces from all di-rections, which act on the abutment teeth via the anchoring components. An elastic anchoring ele-ment transfers forces to the periodontium of the abutment tooth in such a way that, in addition to the normal axial forces, tipping, twisting, and pull-ing forces act on the tooth and load it nonphysio-logically. In periodontally borne and mucosa-borne dentures, elastic anchoring components pro duce statically indeterminate systems that cannot be calculated and are therefore always awed.By means of mobile anchoring elements, main-ly uncontrolled dynamic stresses are transferred to the abutment tooth, which does not occur with a rigid connector; rocking movements on a yield-ing mucosal support can drag the abutment tooth to and fro in its socket until it loosens and is lost. The mucosal support will not withstand such dy-namic stresses caused by a denture base.The natural teeth are also exposed to forces from all directions; they compensate for these forces in a closed dental arch and convert them into physiologic stresses. Elastic anchoring ele-ments with one or more movement possibilities load the abutment tooth and the edentulous parts of the dental arch in an uncontrolled way to the detriment of that tissue.It is assumed that elastic or mobile connections between the residual dentition and the prosthe-sis reduce the loading for the abutment tooth. An elastic connection, however, only alters the loading direction. When a cantilever xed partial denture is loaded perpendicular to the support by masticatory pressure and sinks into the mu-cosal support, a hinge or another elastic connec-tion will convert the intrinsically axial load for the abutment tooth into additional tensile stress in the distal direction, thereby tipping the tooth. In addition, extremely uneven loading of the muco-sal support occurs, which is very pronounced dis-tally and only minimal mesially, in the pressure Fig 5-1 The usual precision ttings for dental anchoring components are fabri-cated by hand but are also available as prefabricated auxiliary parts.Parallel t Conical tSpring tThread tPrimary part (matrix)Secondary part (patrix)Fig 5-2 A parallel tting that connects the residual dentition to a removable res-toration has two structural parts that can be inserted into each other where the matching parts have the same nominal dimensions. The positive geometric structural parts are called patrices, and the negative matched parts are known as matrices. In dental technology, the pri-mary matched part is located on the xed tooth replacement (eg, a crown), and the secondary structural part is located on the removable prosthetic replacement. 131Parallel Fittingshadow under the joint. In the process, the mar-ginal periodontium of the abutment tooth close to the saddle can be crushed horizontally.In a rigid connection (coupling), the vertical masticatory pressure can also lead to tipping of the abutment tooth, but most of the force is transferred axially. This protects the mucosal support in particular. If the abutment tooth is joined to several remaining teeth by splinting, the tipping is balanced by a rigid connection to the denture; conversely, if the connection is elastic, all the splinted teeth are pulled in a distal direc-tion, not least to the detriment of the loaded mu-cosa.A rigid coupling between denture and residual dentition can be achieved with telescopic compo-nents in the form of parallel and conical ttings (Fig 5-3). They should be preferred to elastic con-nections (Fig 5-4).Parallel FittingParallel tting refers to two telescopic structural components in which the tting surfaces run par-allel throughout the entire insertion length—for example, a cylindric drill hole with a xed diam-eter and specic depth into which a shaft of the same diameter is pushed. The shaft can easily be pushed in if the drill hole is slightly bigger, but it cannot be inserted, or can only be inserted with great force, if the shaft is bigger by a simi-lar amount. The accuracy of a parallel t can be ascertained directly from the difference between the diameter of the shaft and that of the drill hole (Figs 5-5 to 5-7).The quality of a technical t is measured by the difference between the internal diameter of the outer matched part and the external diameter of the inner matched part. Depending on the differ-ence in diameters, the following parallel ts can be identied:• Press t exists if the shaft diameter (DS) is great-er than the drill-hole diameter (DDH): DDH < DS• Transition t exists if the drill-hole diameter and shaft diameter are the same: DDH = DS• Clearance t exists if the drill-hole diameter is greater than the shaft diameter: DDH > DSClearance (or play) denotes a positive difference in size; that is, the drill hole is larger than the shaft. Oversize denotes a negative difference in size when the shaft is larger than the drill hole.In mechanical engineering, parallel ttings are produced by a costly process with computer-controlled machine tools in which the dimensions are set and controlled via photoelectric measur-ing devices. The accuracy of these ts is in the re-gion of ten-thousandths of millimeters. With den-tal technology techniques, surfaces polished to a Fig 5-3 Another precision tting in telescopic components is a conical t, which can be used as a rigid anchoring element. Conical ttings are produced by hand as conical (tapered) crowns and industrially as conical attachments.Fig 5-4 A resilient circumferential tting is mainly used as a handmade cast clasp or as a prefabricated stud tting. The elas-tic clasp arms are pushed over the widest circumference of the tooth, engage in the undercuts, and perform a retentive func-tion. 132Telescopic Anchoring and Supporting Elementshigh glaze, for instance, have a surface roughness in the order of several thousandths of millimeters.In mechanical engineering, parallel ttings are generally applied to inseparable connections. In dental technology, however, this t is produced for separable connections with dimensional inac-curacies within the range of a tenth of a millime-ter. The practicability of the different t qualities in dental technology will be analyzed individually: Press t is not used in dental technology because the matched parts can only be pushed on with considerable force. Once the matched parts are brought together, however, elastic deformation (the outer part is widened, the inner part com-pressed) will press the tting surfaces so rmly against each other that they can only be disen-gaged with great difculty. Even greater force is needed to separate the parts than to join them to-gether. The matched parts are wedged together, the tting surfaces can fuse together, and an in-separable connection can arise.Transition t (or snug t) can only be used in certain cases. Joining and separating the matched parts is associated with considerable friction ef-fects, depending on surface roughness. The parts t together snugly as a good but incalculable ad-hesive effect occurs throughout the tting surface. With moderate resistance to static and dynamic friction, a transition t would be highly suitable for anchors in dental technology. However, the friction effects when joining and separating the parts quickly lead to wear of the tting surfaces so that a clearance t without appreciable adhesion results after prolonged use.Clearance t (or loose t) is the preferred type of t. Matched parts can easily be joined and sepa-rated with slight resistance to static and dynamic friction and without any signs of wear, even dur-Clearance tDrill-hole diameter (DDH) is larger than the shaft diameter (DS)Transition tDiameters of the drill hole and shaft are identicalPress tShaft diameter is larger than the drill-hole diameterDSDDHDSDSDDHDDHDS = DDHDS < DDHDS > DDHFig 5-5 The accuracy of a parallel tting is indicated by the match between the dimensions of the shaft and the drill hole; based on the dimensional conformance or difference between the diameters of the two matched parts, three types of t are described.Fig 5-6 One measure of the quality of a parallel t is the size of the tting surfaces that touch each other in a specic design. In ttings for dental technology purposes, this absolute contact area can differ considerably in attachments of the same structural height and width. Furthermore, if the tting surface is interrupted by additional activatable components, the absolute contact area will be further reduced, as shown here in a dovetail tting. 133Error Analysis of Parallel Fittingsing frequent use. Only slight, but calculable, ad-hesive effects occur, which are supported by ad-ditional anchors. The undeniable advantage lies in the fact that the matched parts have a dened path of insertion and end position. Except from the path of insertion, forces cannot lift off the res-toration because a clearance t also provides a rigid connection between the residual dentition and the denture.The quality of t can be determined from the size of the joining and separating forces, which in turn depend on the following:• The size of the clearance• The absolute size of the contact surfaces• The absolute parallelism of the tting surfaces• The contact pressure of the tting surfaces• The surface roughness of the tting surfaces (contact pressure and tting surface roughness must be low to prevent abrasion)Error Analysis of Parallel FittingsThe practical value of parallel ttings is measured by the extent to which they fulll the dened functions of anchoring and supporting elements. While securing the horizontal and vertical posi-tion, dened adhesion and bracing of the residual dentition are ensured by ts that have little clear-ance (play) and absolute parallelism, that do not have any abrasion, and whose matched parts are not displaced. Clearance, parallelism, abrasion, and displacement of the matched parts depend on the technical process.Size of clearanceIn dental technology fabrication processes, the size of clearance depends on several factors. The primary part of the tting is milled; the secondary part is carved out of wax over the primary part, cast, and nished, during which the following procedural and system errors can occur:• Stresses during wax preparation• Expansion inaccuracies of the investment mate-rial• Granulation of the investment material for sur-face roughness• Casting errors, such as blowholes, inclusions, and casting beads• Casting temperature that is too high or too low• Surface treatment errors, such as airborne- particle abrasion, glazing, corrective reduction, and polishingSurface roughness of tting surfacesSize of tting surfaces Parallelism of tting surfacesSize of clearanceFig 5-7 Quality of t. 134Telescopic Anchoring and Supporting ElementsTypical procedural and system errors have such an effect during the fabrication of parallel ttings that all types of t, such as clearance, transition, and press t, occur by chance (Figs 5-8 and 5-9). This is mainly attributable not to the dental techni-cian’s shortcomings but to the special fabrication methods involved in dental technology, which are inadequate for such levels of accuracy.ParallelismA precise cylindric t is difcult to achieve by dental technology fabrication methods because procedural and system errors occur, giving rise to different forms of t by chance. A true cylindric t is an inverted cone that is opposite to the direc-tion of withdrawal or a true cone.Wax processing errorsCasting errorsAirborne-particle abrading with the wrong abrasiveElectrolytic processingGrinding and polishing of tting surfacesFig 5-8 As a result of dental technology processing methods, all three types of t—cylindric t, conical t, and inverted cone—can arise by chance when the aim is to produce a parallel t.Fig 5-9 Error-free fabrication of the secondary part is not possible with dental technology processing meth-ods. Quality of t is inuenced by procedural and system errors, which can add up to an unacceptable total error. 135Error Analysis of Parallel FittingsWhen the parallel surface is being milled, the cutter is guided by hand. As a result, small differ-ences in working pressure can cause a change in the milled surface, and grooves or chatter marks arise (Fig 5-10). If the part being worked is slightly raised or tilted from the base, partially undercut areas will be formed. If the bearings of the mill-ing machine are worn out or if it is not possible to achieve accurate parallel guidance of the milling cutter, no parallel milled surface can be produced. This kind of system error due to the tool and mill-ing machine can easily be overlooked.Abrasion of parallel ttingsWhen the matched parts are joined and separat-ed, dynamic friction takes place throughout the tting surface from the moment the rst move-ment starts until the end position is reached. This friction gives rise to abrasion, which is increased by the following:•The surfaces tting together more tightly; if there is very little clearance, the surfaces slide against each other under greater contact pres-sure•The increased surface roughness of the tting surfacesEven during normal use, a parallel tting will change its shape due to abrasion. After a brief wearing time, a transition t becomes a clearance t, which calls into question the value of this t-ting if no additional anchorage aids are provided.Displacement of individual matched partsFrom model die to tooth preparation in the pa-tient’s mouth, the matched parts can be displaced in relation to each other. In accurate parallel t-tings, even a positional difference of 0.2 mm is problematic enough to jeopardize the success of the whole piece of work. Possible causes of dis-placement include the following:• Inaccuracies in impression-taking; after the try-in, the primary parts are not placed in the correct position in the combined impression• Individual primary parts are shifted on the mill-ing model compared with the original model• Secondary parts have warped during the pro-cessing steps performed• Secondary parts shift in the mouth during ce-mentation because of the space required for the cementThe primary part may also become tilted if both matched parts are cemented in place together in the prosthetic unit. On insertion, great pressure has to be exerted, which can tilt the tooth preparation. Insertion grooves on the prepared tooth may pro-vide the simplest solution in this situation.Working pressure too high; the cutter bendsTilting of the milling model; undercut areasRun-out errors during milling; chatter marksFig 5-10 Precise parallelism can be reliably achieved with primary parts using dental technology processing meth-ods. Procedural errors can occur, however, because the cutter is guided by hand. 136Telescopic Anchoring and Supporting ElementsManually Fabricated Attachment FittingsThe group of parallel ttings includes manually milled attachment ttings because of their mode of action and physical properties. These parallel ttings make up the primary part, which is milled in the replacement crown; the secondary part is xed to the removable replacement. The three classic forms of manually fabricated attachments—ring or cylindric form, horseshoe form, and T-form (Fig 5-11)—were described by Steiger (Zürich) in 1924.The ring or cylindric form is an occlusally open telescope that encircles the replacement crown as a closed ring. To increase the static friction, two channels can be milled approximally, into which the matching pins engage. These pins may comprise resilient wires and are activatable. To brace against axial masticatory forces, a shoulder around the neck prevents the cylindric tting from slipping off. Transverse forces are absorbed by this cylindric attachment, just like a closed tele-scopic crown. An anchoring band clasp is a pos-sible modication.An anchoring band crown is the primary part of this attachment structure in the form of a full crown with circular parallel milling that has a 0.5-mm-wide cervical shoulder. The milled sur-face is interrupted on one approximal surface and has two parallel limiting channels. An anchoring band clasp is a telescopic clasp that is open ap-proximally on one side and placed onto the an-choring band crown as the secondary part. It can be activated to increase the static and dynamic friction effects.The horseshoe form encloses the replacement crown as a semicircular milling into which the ac-curately tting secondary part engages. To in-crease adhesion, approximal channel and pin re-tentions are milled. A bar connection running occlusally and cervical shoulder millings help to secure the vertical position. The pin, channel, and shoulder millings enlarge the static friction sur-face areas and brace the structure. Possible de-signs are the channel-shoulder-pin attachment and the encircling catch with shear distribution arm.The channel-shoulder-pin milling is applied to a veneered crown and runs over the approximal and lingual surfaces. The semicircular tting sur-face ends in a cervical shoulder; it has pin inlets and parallel-milled channels that dene the sur-face area as well as a channel running occlusally (Fig 5-12). The approximal and occlusal channels as well as the cervical shoulder offer the exur-ally rigid frame for the semicircular secondary part; the occlusal surface can be formed by the secondary part. The pins, made of bend-resistant wires, are soldered into the cast outer crown; they are activatable spring pins that increase stat-ic friction. The vertical pins counteract withdrawal forces intraorally. A channel-shoulder milling is a semicircular milling reduced by the pin inlets. The encircling catch is a semicircular parallel milling with a cervical shoulder on the lingual surface of an abutment crown to which a pre-Fig 5-11 Manually milled attachment ttings can be reduced to three basic forms. The cylindric form (as a ring telescope) and the horseshoe form (as a channel-shoulder-pin attachment) are the most commonly used in manual fabrication.T-form, used as a T-attachment in a prefabricated versionCylindric form, used as a ring tele-scope or occlusally open telescopeHorseshoe form used as a half-ring with channels and pin millings 137Manually Fabricated Attachment Fittingsfabricated attachment is tted approximally. The milled surface runs from the attachment over the lingual surface to the opposing approximal sur-face, which has a cylindric end groove that limits the surface area. The milled surface and cylindric milling run parallel to the attachment’s path of in-sertion. The cylindric milling can be conical and widened occlusally; this makes handling easier.The shear distribution arm (balancing compo-nent) is an open semicircular telescope with an approximal stabilizer. The shear distribution arm engages in the encircling catch, aids secure po-sitioning during insertion, secures the horizontal and vertical position, and supports the rigid cou-pling of the prefabricated attachment (Figs 5-13 and 5-14). Encircling catches with shear distribu-Occlusal shoulder millingParallel vertical channelsGuide channel for spring pinParallel sliding surfaceCervical shoulder millingOcclusal transverse channelFig 5-12 The occlusal surface can be formed by the subcrown in a channel-shoulder-pin attachment or be covered by the outer crown (as in the illustration). If there is no cervical shoulder milling, the occlusal surface should be formed by the outer crown, or a sturdy encircling occlusal shoul-der should be milled.Fig 5-13 An encircling catch with shear distributor is used as a stabiliz-ing element for prefabricated struc-tural components and should rigidly secure the vertical and horizontal position for a removable restoration. An encircling catch and shear distri-bution arm run over the lingual sur-faces of the abutment teeth; for po-sitional stability, approximal stabiliz-ing channels are milled parallel to the prefabricated attachment.Fig 5-14 The encircling catch for the shear distribution arm is milled paral-lel to the prefabricated attachment and has approximal stabilization or end channels. If the encircling catch passes over two abutment teeth, the stabilization channel can be prepared as an interlock milling. The cervical shoulder offers vertical positional safeguarding, and the occlusal shoul-der marks the upper end of the milled surface.Prefabricated attachmentInterlock millingParallel millingCervical shoulderOcclusal shoulderApproximal stabilization channel 138Telescopic Anchoring and Supporting Elementstors can also be combined with a resilient anchor-ing component (stud anchor).The T-form or T-attachment is sunk approximally into the replacement crown as a hollow form. The T-shaped secondary part is seated on the remov-able replacement. The shape of a T-attachment requires considerable loss of tooth substance approximally, which may be available because of a very pronounced cavity. The T-form is milled by hand but also used in industrially fabricated attachments. In principle, manually fabricated at-tachment ttings have the same indications as telescopic crowns. The advantage of semicircu-lar channel-shoulder-pin attachments is that they require a smaller space than telescopic crowns because the vestibular portion of the anchoring crown does not have to be double walled.Encircling Catch with Shear DistributorThe encircling catch is milled parallel into a full crown, while the matching shear distributor on a removable replacement is integrated as a sup-porting element. An additional anchoring element has to take on the anchoring function.Encircling catches with shear distributors are the most popular structural forms as stabilizing elements for delicate prefabricated attachments. They are also combined with stud anchors, such as CEKA and ZL anchors (ZL Microdent); in this combination, the encircling catches rigidly secure the vertical and horizontal position, while the stud anchors take on the retentive function. The shear distribution arm can also be combined with a clasp as a splinting element. The basic form of a double-arm clasp with onlay has an active vestib-ular retentive arm and a lingual shear distributor as the guide arm.Following is the fabrication process for an en-circling catch with shear distributor: The tooth is prepared to receive a veneered crown, and the preparation margin is shaped with a pronounced shoulder. The dental tissue usually has to be re-moved more than normal (approximately 1.2 mm). An insertion channel is required to avoid shifts in the model-to-intraoral situation.The veneered crown framework can be pre-pared to receive an acrylic resin or ceramic ve-neer. The primary crown can be veneered with ceramic, which is not possible with a telescopic crown because the ceramic might ake off in re-sponse to dynamic stresses from the outer tele-scope.The milled surface of the encircling catch is let into the framework and is characterized by cervi-cal shoulder milling. The milling of the encircling catch has a threefold function:1. It provides static support.2. The shoulder depth ensures the material thick-ness of the shear distributor.3. It aids stability to prevent bending open.A 0.5-mm-wide metal bar is left between the veneer and the milled surface to reinforce the veneer material. The encircling catch must have a minimum height of 2.5 mm, which means the shape of the anterior teeth may appear bulky. The milled surface ends approximally in the parallel (or conical) end channel, which becomes effec-tive in a lingual direction against transverse with-drawal forces.To brace against the half-ring being bent open and food compaction, the transitions from the milled surface to the occlusal parts of the crown are chamfered or end in occlusal shoulder mill-ing. The encircling catch is waxed up/milled di-rectly into the replacement crown, invested, and cast. During milling of the tting surfaces, it is im-portant to ensure the following:•Milled surfaces are completely parallel.• The milled surface and prefabricated attach-ment lie parallel.• Both portions are parallel in their path of inser-tion.• A milling model with milling base is prepared.The shear distributor is waxed up together with the denture framework. It fully covers the milled tting surfaces and shoulder millings and com-pletes the anatomical shape of the tooth. Its ma-terial thickness is at least 0.5 mm, and the transi-tions overlap slightly so that they can be rened.Manually prefabricated structures place high demands on craftsmanship and have wide t tol- 139Telescopic Crownserances (Fig 5-15). If manually fabricated parallel ttings are combined with prefabricated parallel attachments, the differing t tolerances have an unbalanced effect: The smaller t tolerance of the prefabricated components produces a rmer seat-ing; the prefabricated components have to absorb the bulk of the stresses and are overloaded.Error analysis of the encircling catch• Poor parallelism: If the tting surfaces follow a positive conical course, there is no dynamic fric-tion; static friction depends on the slope of the milled surfaces. If the tting surfaces are nega-tively conical and undercut, the matched parts cannot be joined (Fig 5-16).• Fitting surface is lower than 2.5 mm and the ab-solute contact surface of the tting is too small: This height does not provide stable anchorage against tilting, twisting, or transfer of mastica-tory forces; the area of static friction is also too small (Fig 5-17).• No cervical shoulder and channels are too long: Without a cervical shoulder milling, the vertical position is jeopardized.• No occlusal shoulder but a sharp edge at the margin of the milled surface: As a result, food is easily compacted between the tting surfaces (Fig 5-18).Telescopic CrownsTelescopic crowns are double crowns in which the inner crown is cemented onto the tooth prep-aration and the outer crown is coupled with a re-movable tooth replacement. The tting surfaces of the telescopic components can be worked as parallel or conical ts. A telescopic crown, based on the principle of a parallel t, comprises two structural parts where the inner telescope (pri-mary part) has at least two plane-parallel surfaces facing each other and is completely enclosed by the outer telescope (secondary part), which has the anatomical tooth shape (Fig 5-19).The inner telescope is fabricated by the milling process and has plane-parallel outer surfaces. The parallel surfaces lying opposite each other approximally are usually sufcient for retention, while the vestibular and lingual surfaces can fol-low a conical course. The parallel surfaces must be slightly rough for static friction effects. The surfaces polished during dental laboratory work-ing achieve just the right level of roughness. The inner telescope is cemented onto the tooth prepa-ration, which has an insertion channel for a de-ned path of insertion.When telescopic crowns are combined in a unit, all of the telescopic surfaces must be parallel with the path of insertion. The slightest deviations will cause stresses. The inner telescope is at occlus-HFig 5-15 In the case of man-ually milled encircling catch-es, which are associated with prefabricated attachments, end channels, and occlusal and cervical shoulders, the follow-ing errors occur (see Figs 5-16 to 5-18).Fig 5-16 The tting surfaces do not run parallel. If the tting surfaces and channels are negatively conical and under-cut, the encircling catch and shear distributor cannot be joined together.Fig 5-18 If there are no oc-clusal and cervical shoulders, the shear distributor ends in sharp edges and the vertical position is not secured; food can be trapped between the tting surfaces.Fig 5-17 The height (H) of the parallel tting surface is smaller than 2.5 mm, and the absolute contact surface of the tting is too small; this height is inadequate to ensure positional stability. 140Telescopic Anchoring and Supporting Elementsally and has chamfered transitions to the milled surfaces for ease of positioning during insertion.The outer telescope is removable and has an anatomical shape as a full-cast crown, veneered crown, or occlusally open ring telescope and as a telescopic band clasp (anchor band clasp), which is supported on a circular shoulder on the inner telescope (Fig 5-20). The outer telescope con-tacts the parallel surfaces of the inner telescope evenly throughout the retentive surface from ini-tial placement to the stop. The telescopic parts adhere by means of static and dynamic friction effects; in addition, resilient elements or locking devices may be used.Indications for telescopic crownsTelescopic crowns are used for removable den-tures and removable partial prostheses. The par-allel guided t offers a xed path of insertion and a precisely rigid connection between the denture and the residual dentition in a dened end posi-tion. Telescopic units on several abutments pro-vide excellent bracing of the residual dentition by means of secondary splinting. The hygiene con-ditions are particularly favorable with telescopic crowns.A double-walled crown demands more space and requires greater loss of tooth substance dur-ing preparation than normal replacement crowns (Fig 5-21). Fabrication of a telescopic crown in-volves considerably more work and hence is more prone to error. Additional retentions incorporated into the double crown require further space and involve a more time-consuming technique that is also prone to error.Additional retentive elements for telescopic crowns are mainly prefabricated components in the form of activatable resilient and passive lock-able components. They are elements for primary and subsequent assembly that compensate for inadequate adhesion and provide positional sta-bilization of the matched parts.Activatable resilient elements are prefabri-cated systems that are typically integrated into the outer matched part. The resilient element of the outer crown snaps into a groove on the inner crown and holds the matched parts by a gripping Fig 5-19 Telescopic crowns are one form of parallel t. These double crowns have an inner crown as the inner matched part and an outer crown as the outer matched part. Telescopic crowns are constructed so that at least two opposing external surfaces of the inner crown run parallel. The outer crown has an anatomical shape, and its inner wall is adapted to the inner crown. The cervical crown margin is formed by the inner crown, and the outer crown ends about 2 mm above the cervical mar-gin. A cervical shoulder can be prepared on the inner crown, or the outer crown has a tapered margin that is technically dif-cult to produce and is usually unstable.Fig 5-20 The occlusally open ring telescope is a special form of telescopic crown. The telescopic part is a ring that is sup-ported by a cervical shoulder in the inner telescope or by an occlusal shoulder. The advantage of an occlusal shoulder on a ring telescope is that no food collects between the matched parts because the gap between them is horizontally directed. 141Telescopic Crownseffect (Fig 5-22). Numerous intracoronal retentive components are available from various manufac-turers; their spring elements are activatable and replaceable (eg, Pressomatic [Romagnoli], Ipso-clip [Guglielmetti; Fig 5-23], snap attachment, leaf springs). Activatable components can be over-stretched so that the periodontium is overloaded when the telescope is withdrawn. Excessively large clearance ttings cannot be stabilized with these retentive components.Components subsequently mounted for worn matched parts are mainly rubberlike nubs that are stuck into the outer crown. An angled depression is milled into the outer telescope, and the rub-ber nub is set in place so that a slight elevation is formed on the tting surface and rubs on the inner telescope.Therefore, the requirements of telescopes are the following:• Easy to join and separate the matched parts• Dened end position as a rigid connection• Retention in resting position by static friction• Abrasion-resistant t• Delicate periodontally hygienic shapeFig 5-21 A double-walled telescopic crown requires more space than a normal-walled crown, which is why the tooth has to undergo more extensive corrective reduction. Relatively clumsy forms of outer telescope often result, however, be-cause the parallel walls of the inner telescope do not support the anatomical tooth shape. If only the approximal surfaces are placed parallel, relatively delicate shaping of the vestibular sur-face is possible.Fig 5-22 An active anchorage aid in the form of a spring bolt is housed in the outer telescope, which engages in a groove in the inner crown in the resting position. A notch occlusally on the inner telescope allows the spring bolt to be securely joined.Component cap Coil spring Spring bolt Component sleeveFig 5-23 The parts of the additional spring bolt an-chor, here the Ipsoclip, are delicately constructed so that they can be housed in the outer wall of the secondary part. The spring bolt and coil spring are replaceable. 142Telescopic Anchoring and Supporting ElementsConical FittingsConical crowns (after K. H. Körber) are manually fabricated ttings in the form of telescopic double crowns. The primary part has the positive shape of a cone and is referred to as the inner cone or inner crown; the secondary part is known as the outer cone or outer crown and has an anatomical tooth shape.The cone is truncated and ts into an analogous hollow cone, where the external surfaces of the truncated cone are parallel to the internal surfac-es of the hollow cone (Fig 5-24). In engineering, a cone is dened by the height of the truncated cone, over which the diameter changes by 1 mm (Fig 5-25). The occlusal diameter of the primary part of a conical crown is smaller than the diam-eter in the cervical area.The surfaces of a cone can be extended as far as the original cone. The angle of the cone lies in the apex of the cone. Halving this angle by the central axis of the cone gives the angle of taper.LD1D21 mmFig 5-24 A cone means a truncated cone that has side walls sloping toward each other. A conical crown is a double crown in which the inner crown displays the positive shape of a cone. The tting surfaces of the double crown run parallel. A conical tting is a separable join.Fig 5-25 The cone is a truncated cone that changes diameter by 1 mm over a specic height; this is the degree of taper of the cone.Fig 5-26 The slope of the side walls of a cone can be deter-mined by the angle (α) to which a cone can be extended. The angle of taper is half the cone angle (α/2). The taper angle indi-cates the sloping of the side walls to the perpendicular. The taper angle can be measured with a parallelometer. The angle between the parallelometer rod and the cone wall gives the angle of taper.Fig 5-27 The tting surfaces of the conical crown come in contact in the end position, and static friction arises. If the outer cone is exposed to contact pressure FA, a ank force that is vertical on the tting surfaces occurs at the surfaces and is referred to as normal force FN. The magnitude of static friction forces depends on the taper angle.FAFNFN 143Conical FittingsThe angle of taper can be measured between a parallelometer pin and the surface of the cone (Fig 5-26). Therefore, the taper angle is dened as the machining angle between the outer surface of the cone and the parallelometer axis. In dental technology, this taper angle is used to describe the conical shape because the adhesive force of the conical t can be specied with this angle.The central axis of a cone lies parallel to the path of insertion. The taper angle can be measured on the basis of this path of insertion. In some cases, the central axes of individual cones of a combina-tion of abutments differ from the path of inser-tion; one cone surface runs parallel to the path of insertion, and the other cone surfaces are at a positive angle to the path of insertion. This occurs if abutment teeth are excessively tilted toward each other.The adhesive force of a cone does not arise un-til the inner and outer crown touch in the resting position. In a parallel t, dynamic friction occurs from initial contact between the tting surfaces until the matched parts are fully pushed inside each other. If a cone is placed in a matching hol-low cone, adhesion ensues when the plane sur-faces of the two parts come into contact in the end position.Dynamic friction and abrasion do not occur in a conical tting because the tting surfaces only touch when the end position of the structure is reached; these surfaces do not slide against each other in contact. If a telescopic conical tting is joined together, the cone surfaces do not rest loosely but press against each other; thus, more pressure is applied to the outer part. The inner cone is pushed into the outer crown like a wedge, whereby the outer crown is subject to slight elas-tic deformation. The contact surfaces press rmly together and static friction arises (Fig 5-27).The physical principle of the adhesive force, which depends on the contact force due to inser-tion and masticatory pressure as well as on the taper angle, can be explained by a wedge (Fig 5-28): If differently pointed wedges are driven into a block of wood with the same force, a pointed wedge will penetrate deeply and remain rmly in position, a blunt wedge will have difculty pene-trating the wood and can easily be removed, and an even blunter wedge will not penetrate but will repeatedly pop out.The relationship between adhesive force and ta-per angle can be determined by calculations and experimental tests and can be graphically repre-sented: The degrees are plotted on the horizontal Fig 5-28 Comparison with a wedge shows that the size of the taper angle has a direct inuence on the adhesive force of the cone: The smaller the taper angle, the steeper the wedge, the larger the anks, or the larger the normal forces on the sides of the cone. If the taper or wedge angle is larger, the ank forces decrease and may reach the point where the wedge or the cone comes off. This happens because the slope forces be-come greater than the static friction forces. 144Telescopic Anchoring and Supporting Elementsline (abscissa or x-axis) and the corresponding adhesion values on the vertical line (ordinate or y-axis). A small taper angle produces high adhe-sive force, whereas a large taper angle has little or no adhesive force (Fig 5-29).In relation to adhesive force and taper angle, Körber identies three types of cone (Figs 5-30 and 5-31):• Adhesive cone (adhesive anchor) with a taper angle of 5.5 degrees (cone angle of 11 degrees)• Normal cone (normal anchor) with a taper angle of 6 degrees (cone angle of 12 degrees)• Support cone (support anchor) with a taper an-gle of 6.5 degrees (cone angle of 13 degrees)Groups of conical crowns can be fabricated in which crowns with different taper angles between 5.5 and 6.5 degrees produce different adhesive forces:Fig 5-29 The adhesive force of a cone depends on the angle of taper. According to Körber, the mean values for adhesive force can be dened for three angles of taper of function-related cones: A 5.5-degree angle of taper produces a retentive anchor with approximately 10 N of adhesive force; a 6-degree angle of taper produces a normal anchor with approximately 6 N of ad-hesive force; and a 6.5-degree angle of taper produces a sup-porting anchor with approximately 5 N of adhesive force.Fig 5-30 The most favorable taper angle for dental technology constructions is 6 degrees, which is equivalent to a cone angle of 12 degrees. If, in the case of tilted teeth within a group of tapered crowns, the cone axis does not coincide with the tooth axis, this difference can still be tolerated within a range of up to 12 degrees. The chosen path of insertion is the axis, which is used as the reference for the taper angle. If an angle of 8 degrees is chosen on one side and an angle of 4 degrees is selected on the opposite side, this gives a cone angle of 12 degrees.Fig 5-31 To give the inner crown an evenly thin wall thickness, the taper angle of the different sides of a crown can vary. The only decisive factor is that the total of the opposing angles re-sults in the desired cone angle. If a cone angle of 12 degrees is chosen, the total of the opposing taper angles must result in exactly this number of degrees. For a normal adhesive cone, 12 degrees is appropriate. If the cone adheres very strongly, a cone angle of less than 12 degrees must be selected.Path of insertion 145Practical Value of Conical Fittings• Taper angles less than 5.5 degrees produce ex-cessive adhesive forces (several times the con-tact pressure)• Taper angles greater than 6.5 degrees no longer have dened adhesive forceThe advantage of conical crowns lies in the fact that, as with other conventional ttings, adhesive force is xed beforehand and can thus be exploit-ed for therapeutic purposes.Practical Value of Conical FittingsFigure 5-32 illustrates the fabrication of a tapered crown construction. In the case of conical ttings, the adhesive force can be variably xed, depend-ing on taper angle and hence the retention of a partial prosthesis. They come apart without any dynamic friction effects and thus show virtually no wear and tear.1. A die is produced, and the prepara-tion margins are exposed and marked.2. The die is set up in the parallelometer. A path of insertion is selected at which the undercuts are smallest on all the tooth preparations.3. Subcrowns are carved in wax; opposing surfaces exhibit the cone angle.4. A special hard rubber polishing wheel is used to polish the cone on the tting surfaces without a high-glaze nish.5. The crown margin is polished to a high glaze and kept clear of the peri-odontium; this makes the edge of the cone visible.Fig 5-32 Schematic illustration of the fabrication of a tapered crown construction. 146Telescopic Anchoring and Supporting ElementsFig 5-33 Conical ttings can be assem-bled even when there are fabrication in-accuracies. (1) A cone-shaped drill hole is created, and the cone ts accurately. (2) The cone is too big, but the tting sur-faces have static friction contact and per-form their function. (3) The cone is too small and slips more deeply into the drill hole; it fullls the necessary retentive function. (4) The angle of the cone is larg-er than that of the drill hole; the cone be-comes wedged in the drill hole and holds. (5) The angle of the drill hole is larger than that of the cone; the cone be-comes wedged in the drill hole and holds. In the case of tapered crowns, these kinds of errors are tolerated within a group of crowns.Processing errors can be tolerated (compensat-ed for) by conical crowns to a certain extent (Fig 5-33). For example, casting inaccuracies due to incorrect casting construction are fully tolerated by the cone because the t does not alter with different tolerances of crowns. An oversized outer crown can be positioned more deeply, and an un-dersized outer crown cannot quite be pushed into place. There is no difference in adhesive force.Groups of conical crowns can be used because of ease of insertion and contact closure of the dental arches; the conical crown nds its end po-sition by itself. When conical crowns are fabricat-ed with good accuracy of t, a complete marginal seal is also attained, which prevents odor buildup under the crown.Cone tolerance refers to the characteristic of conical ts to compensate for positional varia-tion between the model and intraoral situation in single conical crowns forming part of a group of conical crowns. If the conical crowns for a group of abutments are made separately based on one path of insertion, positional discrepancies occur between the model situation and the intraoral situation; the individual crowns can be rigidly joined together based on a new impression of the real intraoral situation without impairing the t of the crown unit. This can only be done, however, if the positional discrepancies are within the range of the taper angle. Conical crowns can always be slimmed in the occlusal area, thereby approach-ing the natural tooth shape.Restoring partially edentulous dental arches with abutment teeth converging toward the path of insertion is easier with a conical unit than with parallel ttings (Fig 5-34). The inclined tooth prep-arations are tted with conical subcrowns that are all related to one path of insertion (Fig 5-35). In the edentulous area narrowed by convergence, small taper angles can be used that are offset by the complementary angle on the opposite side of the crown.Disadvantages of conical crownsIf the outer crown is oversized due to casting faults, this error can be compensated for by trim-ming the inner crown by the necessary amount so that the outer crown can be positioned more deeply. A cone treated in this way will t and ad-here, but the occlusal relationship with the an-tagonist will be disrupted by the amount to which it is placed more deeply. Where occlusal surfaces are accurately reconstructed, this is an error that cannot be tolerated.If the outer crown is undersized, hence too small, the result is a vertical increase of occlusion, which the patient cannot be expected to tolerate. A possible remedy might be targeted polishing of the inner crown to remove material. This is dif-cult, however, because the material is not re-moved evenly. The inside of the outer crown could also be treated (possibly by airborne-particle abra-sion). In both cases, the coefcient of friction is 1 2 3 4 5 147Practical Value of Conical Fittingsaltered by the surface roughness; the taper angle at the machined surfaces usually varies as well. The adhesive force of the cone, which could be precisely determined by means of the taper an-gle, is now altered in an uncontrolled way.Discrepancies in the accuracy of t lead to oc-clusal interferences if the outer crown has a com-plete occlusal relief. If the outer crown is subse-quently veneered occlusally, this source of error can be corrected. Discrepancies in the taper angle between the matched parts lead to pronounced interferences because the matched parts only have linear contact and are wedged into each other. The adhesive forces can no longer be calcu-lated when this wedging happens. Discrepancies in the position of individual cones from the model situation to the intraoral situation are tolerated if the discrepancies remain within the range of the taper angle, but occlusal interferences may be expected here too if the outer crown contains an occlusal relief adapted to the antagonist.The major disadvantage of a conical t is that the adhesive force depends not only on the ta-per angle but also on the joining forces of the matched parts. As a result of masticatory force, a conical crown can become wedged onto the sub-crown in such a way that the permitted limit for adhesive force of 10 N is greatly exceeded.Fig 5-34 Restoring a partially edentulous dental arch with con-verging tooth positions is particularly difcult. A normal xed partial denture cannot be inserted if the tooth preparations have undercuts. Such a xed partial denture ought to be a two-part construction joined together with a screw connection once it is in the mouth.Fig 5-35 A partial denture with tapered crowns may be the solution even when teeth are extremely tilted. The undercut tooth preparations are tted with conical subcrowns that are all referenced to one path of insertion. The tapered crown partial denture can be inserted without difculty. A removable partial denture also offers the advantage of more favorable periodon-tal hygiene. 148Telescopic Anchoring and Supporting ElementsIndustrially Fabricated Attachment FittingsIndustrially fabricated attachment ttings are also referred to as structural components, prosthetic auxiliary parts, prefabricated components, or pre-cision attachments. Prosthetic auxiliary parts are structural components in the form of two-part telescopic (parallel) ttings in very small dimen-sions that comprise the primary part on a xed crown and the secondary part on a removable restoration (Fig 5-36). Soldering plates or reten-tive components are mounted on the two matched parts, and these can be used to create an insepa-rable connection to the xed crown on the one hand and to the removable replacement on the other hand.These prefabricated components do not differ from the previously described parallel ttings in their function and physical characteristics. They have tting surfaces with high accuracy and mini-mal clearance. The reason for this accuracy lies in the method of manufacture. The prosthetic aux-iliary parts are produced with high-grade, com-puterized, special machine tools in small batches.The matched parts are fabricated using computer- controlled, metal-cutting shaping techniques (such as turning, milling, and drilling) or in suitable cold-forming processes (such as drawing or punching). These two cold-forming processes, as well as the metal-cutting techniques, are ideal for producing precise matched parts, so the term precision at-tachment justiably applies. Complicated molded parts are produced in high-standard precision casting processes.Physical material properties, such as strength, hardness, abrasion resistance, and surface smooth-ness, are achieved as a result of the specic mate-rials. In addition to having these physical charac-teristics, the materials have to be biocompatible (ie, tolerated by the tissues). Because they are also soldered or cast onto porcelain-fused-to-metal structures, they need to be especially high fusing and heat resistant. These materials must also not be altered by special dental technology process-ing methods, such as acidifying, glazing, or other electrolytic methods. Generally speaking, the matched parts consist of proven precious metal alloys such as gold-platinum, platinum-iridium, and silver-palladium. Resilient components of these attachment ttings (springs, spring pins, leaf springs, screws, and pins) are fabricated from special high-grade steels.The tolerances of the matched parts are a hun-dredth of a millimeter and are in keeping with the surface quality of the tting surfaces. Smaller tolerances (ie, less clearance) would cause ex-cessive static friction effects so that the matched parts could only be separated applying consider-able force and would wear unduly. The absolute contact area is not the measurable size of the tting surfaces but the actual contact area of the metallic matched parts. The absolute contact area is smaller than the measurable size of the tting surfaces because the metal surfaces can only have partial contact because of surface roughness. If there is minimal clearance, the t-ting surfaces are brought closer together; that is, the absolute contact area becomes larger, as does the static friction.The high accuracy of t and low tolerances en-sure the dened static and dynamic friction resis-tance. If the absolute size of the contact area or the minimal height of the tting surfaces is insuf-cient for retentive force, additional resilient or locking retentive components are mounted. The size of the contact area decreases if retentive parts lie within the tting surfaces. To support horizon-tal and vertical positional stability, the delicate components are usually prepared in conjunction with a circular notch and a shear distribution arm.An extensive range of prefabricated attachment ttings is available. Manufacturers produce cata-logs of prosthodontic auxiliary parts that describe the individual ttings in terms of their application and function. Classication criteria for prefabri-cated attachments can be derived from the differ-ent geometric prole shapes of the matched parts. The two types of attachments are box-shaped and cylindric attachments. Box-shaped proles can be shaped like T, double-T, or H attachments. In the case of cylindric proles, one matched part can be constructed as a roller and the other as a ring-shaped sleeve. The most common prole shape for parallel attachments is a double roller or rounded T shape, in which the prole blades can be spread apart to activate the attachment (Figs 5-37 and 5-38). 149Industrially Fabricated Attachment FittingsRetention sleeveRetention housingFixing screwProximal barSecondary part barSliding surfaceActivation bodyChamferActivating slotActivating threadFixing threadOcclusal surfaceSliding surfaceActivating slotSide surface primary partProximal sliding surfaceBase surface primary partProximal barSecondary part barAttachment headRetention sleeveActivation bodyProximal sliding surfaceChamferBar sliding surfaceFig 5-36 Industrially fabricated attachment ttings have two telescopic components with dened t tolerances. The primary matched part is integrated into the crown, and the secondary matched part is xed to the removable restoration. The geometric prole of an attachment can be box shaped or cylindric and determines the size of the sliding surfaces, which are supplemented by the bar and proximal sliding surfaces.Primary part Secondary part Primary partBar sliding surfacesProximal sliding surfacesSliding surfacesSecondary partFig 5-38 Secondary part with retention sleeve, activating slot, and activating thread; chamfering of the attachment head makes it easy to join the attachment parts together.Fig 5-37 A T-attachment or double roller attachment can be derived from the box-shaped or cylindric prole shapes, representing the modern design of an activatable and replaceable attachment, for example, the multi-CON from DeguDent or the DuoLock at-tachment from ZL Microdent. 150Telescopic Anchoring and Supporting ElementsPractical Value of Prefabricated AttachmentsFigure 5-39 outlines the practical value of differ-ent attachment designs. Prefabricated attach-ment ttings can be used for any type of remov-able tooth replacement. They make it possible to restore dentition in difcult cases because the space required for a prefabricated attachment is generally less than that required for manually fabricated ttings. Prefabricated attachments can be easily and reliably worked. Prefabricated n-ished parts can be mounted within crowns (intra-coronally), outside crowns (extracoronally), and between crowns (intercoronally) as well as onto root crowns and in very small edentulous gaps. They can be used as separable or partly separable connectors.Full-cast crowns and closed veneered crown frameworks are most suitable for receiving pre-fabricated attachment ttings. The retentive surfac-es of the veneers must be clearly separated from the anchoring surfaces of the attachment ttings.The primary part can be xed to the crown framework by a variety of methods. It can be sol-dered or joined in the casting process; less com-monly, the primary part is bonded in place. The primary tting surfaces can also be integrated into the crown framework in the erosion process or by a spacer technique. Secondary parts can be xed in the denture saddle with acrylic resin, sol-dered, or bonded to the model casting base. For this purpose, the soldering or bonding surface is prepared on the metal base.The quality of prefabricated nished parts is measured by the extent to which they perform the required functions of anchoring and support-ing elements. Differentiation is therefore based on the nature and extent to which function is ful-lled, giving rise to the following distinctions:• Intracoronal and extracoronal attachments, which affect periodontal hygiene• Activatable and passive attachments, which af-fect the dened retentive force• Rigid and articulated/elastic attachments, which affect horizontal positional stability• Open and closed attachments, which affect verti-cal positional stabilityPeriodontal hygieneIntracoronal (also paracoronal) positioning exists if the primary part is sunk into the approximal out-er wall of an anchoring crown. For this to happen, either the tooth preparation must be substantially reduced and the crown wall made thicker, or the primary part must be constructed to be very at. The interface to the marginal periodontium is not covered, and the tting surfaces and the bottom of the tting surfaces lie within the crown contour. This is the correct design in terms of periodontal hygiene, as in a normal coronal restoration.Extracoronal positioning arises if the primary part is placed outside the approximal crown wall and the marginal periodontium is permanently covered. This is unfavorable in terms of periodon-tal hygiene. Encapsulation, suction, and compres-sive effects on the gingiva, due to slight denture movements while functioning, will occur at the interface. The mucosa will proliferate in this area, which can result in inammation.The different positioning of an attachment t-ting does not inuence transfer of forces, provid-ed the tting results in a true rigid connection. If the replacement crown is rigidly connected to the denture body via the attachment, it is irrelevant whether the join is tted inside the crown, on the side of the crown, or farther away in the denture body. The positioning may be important in attach-ment ttings with several degrees of freedom, which, besides the path of insertion, permit move-ment in other directions. In this case, accurate analysis is required to identify how this additional degree of freedom may affect the periodontium of the abutment tooth and the loaded mucosa.Dened retentive forcePrefabricated attachment ttings have dened adhesive forces because of small tting toleranc-es, or they are activatable by means of nely ad-justed spring components. In passive (nonactivat-able) attachments, the initially adequate static friction effects are lost because of abrasion; then the ttings only ensure horizontal and vertical po-sitional stability. The activatable secondary parts are either divided into blades that can be spread apart, or they have additional spring elements that engage in notches on the primary part. Acti-vatable spring components or secondary parts are usually replaceable. 151Practical Value of Prefabricated Attachments Periodontal hygiene Protects the interfaceDened retentive forcePerforms a retentive functionHorizontal positional stabilityProvides physiologic couplingVertical positional stabilityProvides periodontal supportIntracoronal positioning of the primary part is favorable in terms of periodontal hygieneExtracoronal positioning is unfavorable in terms of periodontal hygiene (gingival irritation may occur)Activatable attachment parts offer permanently dened retentive forcesNonactivatable primary parts offer temporarily dened retentive forces via t tolerancesRigid coupling between the denture and the residual dentition secures the horizontal positionArticulated coupling between the denture and the residual dentition does not secure the horizontal positionClosed attachments provide vertical positional stability and periodontal transfer of forcesOpen attachments do not offer vertical positional stability or periodontal transfer of forcesPractical attachmentImpractical attachmentFig 5-39 Differentiation of attachment designs based on their functional and practical value. 152Telescopic Anchoring and Supporting ElementsOne degree of freedomTwo degrees of freedomTwo degrees of freedomTwo degrees of freedomThree degrees of freedomFour degrees of freedomFive degrees of freedomPositional Stability with Prefabricated AttachmentsAnchoring and supporting elements are intend-ed to secure the horizontal and vertical position. Horizontal positional stability means preventing shifting, twisting, and tipping of the denture in the horizontal plane. Vertical positional stability means that vertical masticatory forces are largely transferred axially onto the periodontium of the abutments.The rigid coupling between the denture and the residual dentition with a rigid attachment pro-vides horizontal and vertical positional stability. The connection quality of attachments is dened by the amount and direction of movements pos-sible, which can be expressed as degrees of free-dom. Degrees of freedom indicate the free move-ments that are possible independently of each other (Fig 5-40). Connecting components can have the following degrees of freedom:• Rotation about three axes, equivalent to three degrees of freedom• Translation in three spatial planes, equivalent to another three degrees of freedomStructural components with several degrees of freedom provide no rigid coupling. Prefabricated connecting components can be distinguished ac-cording to the number of degrees of freedom:• A closed attachment tting with a depth stop permits movements of the denture part perpen-dicular to the alveolar ridge only via the peri-odontium of the abutment tooth (one degree of freedom) (Fig 5-41).• An open attachment tting without a depth stop allows movements of the denture part parallel to the alveolar ridge (two degrees of freedom) (Fig 5-42).• A resilient attachment enables movements of the saddle parallel to the alveolar ridge to a lim-ited extent as far as the shifted depth stop (two degrees of freedom) (Fig 5-43).• A hinge joint with a closed attachment allows rotary movements of the saddle about a xed pivot point (two degrees of freedom) (Fig 5-44).• A hinge joint with an open attachment allows parallel displacements and rotary movements of the saddle (three degrees of freedom) (Fig 5-45).• An open ball-head attachment permits tipping and twisting as well as vertical movements of the saddle (four degrees of freedom).Closed attachment ttingOpen attachment ttingResilient attachment ttingHinge with closed attachmentHinge with open attachmentOpen ball-head attachmentOpen spring-loaded ball jointFig 5-40 Classication of attachments according to degrees of freedom. 153Positional Stability with Prefabricated AttachmentsLRLRFig 5-41 When evaluating attachment ttings, determining possible movements of the connected denture saddle within and outside the path of insertion is important. A closed attach-ment tting permits no movement of the denture saddle, ex-cept what is required for insertion and removal. This attach-ment tting is absolutely rigid because vertical masticatory forces are transmitted fully via the depth stop.Fig 5-42 An open attachment tting without a depth stop per-mits movement of the denture part parallel to the alveolar ridge. This attachment tting is not rigid and cannot transfer any axial masticatory forces. The horizontal position is secured against transverse thrusts.Fig 5-43 The resilient attachment is a compromise between closed and open attachment ttings. The depth stop is placed so that the denture saddle can be moved toward the mucosa in the path of insertion. As a result, the mucosa absorbs part of the masticatory force before the periodontium is loaded. Resil-ience leeway (LR) must be determined individually for a denture structure.Fig 5-44 A closed attachment tting with a joint has several possible movements besides the path of insertion. These at-tachments have two degrees of freedom: the limited move-ment in the path of insertion and the rotary movement of the hinge.Fig 5-45 If a hinge is combined with an open attachment in which vertical movement is not limited, the denture saddle can settle into the mucosa parallel to the path of insertion and per-form rotating movements. Horizontal positional stability is merely conned to bracing against tipping off sideways; apart from that, the mucosa has to absorb all the masticatory pres-sures. This kind of structure is outmoded and should be re-jected. 154Telescopic Anchoring and Supporting Elements• A spring-loaded ball attachment permits move-ments in all directions relative to the mucosa (ve degrees of freedom).Closed attachments have only one degree of freedom in the vertical plane: These are box-shaped parallel attachments with a depth stop, in which the secondary part can only be pushed in as far as this depth stop, usually the oor of the primary part. A rigid connection between the den-ture and the residual dentition is achieved be-cause tipping, displacement, and twisting move-ments are prevented and periodontal support takes place. A closed attachment produces a peri-odontally borne restoration. A closed attachment can be placed intracoronally and extracoronally. If the attachment is closed at the bottom, the cleaning possibilities are limited, so the vertical position of the secondary part may be disrupted because of a buildup of tartar. A free-end saddle is anchored with rigid con-nectors and not with an attachment that has sev-eral degrees of freedom. Severe tipping stresses on the abutment teeth are absorbed by the splint-ing of several abutments.Attachments with several degrees of freedom permit movements of the denture in one, two, or all three spatial directions. They are resilient com-ponents, loose guides, and true hinge joints with return mechanisms, which restore the denture to the original position when the strain is relieved. The support on xed abutment teeth and yielding mucosa produces mechanically indeterminate sys-tems with all the disadvantages of mixed-support dentures:• No true distribution of load occurs between the periodontium and the mucosal support.• Distal parts of the jaw and marginal periodontal tissue in the interface are destroyed.• Abutment teeth and jaw segments are non-physiologically loaded by idle movements; the patient plays with the mobile denture.• Mobile connectors wear out badly after a short period of wearing.• The denture becomes deeply embedded.• Occlusal contacts are lost.• Transverse stresses loosen the abutment tooth.Mobile connecting components provide very un-satisfactory positional stability and should there-fore be rejected.Open AttachmentsIn an open attachment, the tting surfaces are fabricated in the path of insertion without a depth stop; they secure the vertical position. The sec-ondary part can be pushed into the primary part to any chosen depth. In principle, the secondary part can be pushed fully through the primary part. An open attachment permits movements of the denture saddle parallel to the path of insertion, and it can settle into the mucosa.A bounded saddle, anchored in this way, is guid-ed axially and supported on the mucosa when loaded by masticatory pressure; this produces a mucosa-supported prosthetic restoration. The in-dication for open attachments is very limited. Only cantilever xed partial dentures with an ex-tensive base (snowshoe principle) can be an-chored better with an open attachment than by the use of normal clasps with an occlusal rest re-mote from the saddle. This is because open at-tachments secure the horizontal position and guide the free-end saddle parallel, which produc-es even mucosal loading. Open attachments have to be positioned extracoronally and must cover or touch the mucosa in the interface region; they are easy to clean.Open attachments prevent tipping and twisting of the denture via vertical guidance and secure the horizontal position, but there are still several disadvantages of their use:• Axial masticatory pressures are not transferred to the periodontium.• There is no support on the residual dentition.• Involved jaw segments are overloaded and at-rophy. • Denture components become embedded.• Occlusal contacts are lost.• The marginal periodontium in the interface is destroyed by mechanical effects.• Antagonists elongate and become displaced.Industrially fabricated open-attachment ttings are mainly supplied in rod lengths (rollers with 155Open Attachmentssleeves), from which the desired length is cut off and integrated into the anchoring crown. Starting from the denture base, a rigid cover is guided onto the primary part, which then covers the at-tachment as an occlusal rest and performs the function of securing the vertical position. This gives rise to a closed attachment with an occlusal stop on the secondary part.Resilient attachments have a displaced depth stop that allows the denture saddle to rest on the mucosa in the resting position. In response to masticatory pressure, the mucosa is loaded rst; when the resilience of the mucosa is exhausted, the secondary part settles onto the displaced depth stop, and axial forces are transferred to the periodontium of the abutment tooth. There is re-silience leeway (interocclusal clearance of approxi-mately 0.2 to 0.5 mm) between the internal and external tting, but it closes in response to masti-catory pressure as mucosal resilience is exhaust-ed; only then is the periodontium loaded. The depth stop can be adapted to the individual resil-ience response of the mucosa. The result is a den-ture with mixed (mucosal/periodontal) support.In severely reduced residual dentitions, resil-ient attachments are indicated if the remaining dentition is inadequate for complete periodontal support, whether due to periodontal insufciency or statically unfavorable distribution of the re-maining teeth. These concepts are put into prac-tice in complete dentures that cover the existing remaining teeth with resilient telescopes or bar-connected root crowns with resilient attachments (overdenture). The prosthesis in extended form is guided vertically by the remaining teeth, horizon-tal tipping and twisting are prevented, and mas-ticatory forces are absorbed by the periodontium in a weakened form.Overdenture prostheses can be supported in the mandible on the root crowns of the canines, which are connected by a Dolder resilient bar at-tachment where the bar clip has the required re-silience leeway (Fig 5-46).Clinically, resilience leeway cannot be mea-sured accurately, which means either overloading of the mucosa or overloading of the periodonti-um occurs if the leeway is too small. Settling and loss of resilience leeway occur after lengthy wear-ing times, which ultimately calls into question the whole concept. Atrophy of the periodontium is possible if the abutment teeth are only loaded by masticatory pressure above mucosal resilience but otherwise remain inactive.Fig 5-46 An overdenture prosthesis with a Dolder bar has a resilience leeway, which means the mucosa has to absorb loading from masticatory pressure. The Dolder bar anchorage permits rotating movements around the bar axis, which means the denture tilts toward the mucosa. The Dolder bar (jointed bar) has three degrees of freedom: a limited movement within the path of insertion as the resilience leeway, a rotary movement around the bar axis on bilateral loading of the denture, and tilting toward the axis of rotation on unilateral loading. 156Telescopic Anchoring and Supporting ElementsFig 5-47 Internal parts of bars can be tted in a straight line or following the curvature of the alveolar ridge.Fig 5-48 The proles of bars can be divided into round and parallel-sided shapes.BarsBars are manually milled or prefabricated metal connectors between crowns, root crowns, and implant posts. They serve to anchor and support partial dentures in a severely reduced residual dentition. Bars can run in a straight or curved line between the anchoring abutments (Fig 5-47). They can be round, egg shaped, or parallel sided in pro-le (Fig 5-48); they can be tted with additional re-tentive components (eg, stud anchors [Fig 5-49]), or they can carry activatable bar sleeves.Bars or internal parts of bars are referred to as bar-type attachments with a parallel-sided angular cross-section. Both manually milled and indus-trially produced components have an occlusally rounded rectangular prole. For reasons of peri-odontal hygiene, they lie approximately 2 mm away from the mucosa (Dolder bar attachment) or are shaped as contact bars.Internal parts of bars are tted with parallel-sided bar sleeves as supporting and anchoring bars; as secondary parts, these provide the dened retentive force by means of static and dynamic friction effects. The Gilmore clip system is a pre-fabricated bar sleeve that can be placed directly in an acrylic resin base. Rod-type bars are prefabri-cated square bars with double-conical drill holes into which activatable stud attachments engage.Bar connectors can be used to create primary, permanent splinting situations. As a result, the re-sidual teeth are rigidly connected to each other and formed into a mechanically solid, functional resistance block that secures the horizontal and vertical position of the denture. Even distribution of stresses becomes possible with full splinting, in which all the teeth are encompassed in the splint-ed group; where partial splinting is performed, only individual teeth are connected with bars.Round bars or bars with a drop-shaped (oval) prole have activatable bar sleeves that, once in-serted, engage over the widest circumference of the bar prole and ensure dened retention by means of spring forces. The bar sleeves permit movement of the denture around the bar axis and are known as bar joints or resilient bars.A Dolder bar joint is a prefabricated, resilient, articulated bar with an oval prole in which the apex is placed nearest to the alveolar ridge. The resilient bar sleeve is adapted to the bar and has Rectangular inter-nal part of bar as a bar attachmentRound or oval bar with articulated effectOval-conical bar with resilience leewayFig 5-49 Prefabricated bar systems are tted with anchor eye-lets for stud anchors. They provide static positional stability but are unfavorable in terms of periodontal hygiene. 157Barsto be widened over the bar curvature when be-ing joined and separated. Resilience leeway is created between the sleeve and the bar. This bar attachment is placed in a straight line between two remaining teeth where it has three degrees of freedom:• Rotation around the bar axis on symmetric load-ing• Rotation around an eccentric axis; on one-sided loading, the bar sleeve sinks toward the loaded side• Vertical translation on central loading over the bar, then the bar sleeve sinks onto the barAny movement of the denture leads to elastic de-formation of the bar sleeve, and the denture is re-turned to its resting position on relief of loading.Resilient bar articulated attachments (eg, Dolder bar) are used in a residual dentition of two teeth between which a straight bar can be laid onto the middle of the alveolar ridge. Canines are the pre-ferred abutment teeth in the mandible. Perform-ing corrective reduction of the abutment teeth down to the roots will shorten the extra-alveolar lever arm of the abutments and thereby reduce their tipping stress.Resilient bar dentures have high retention and secure seating; masticatory pressure is trans-ferred from the whole denture base onto the mu-cosa. After the resilience leeway is exhausted, the bar still has a supporting function. To secure the horizontal position, primary bar splinting offers an adequate resistance block.Hinge joints, which have limited freedom of movement, can roughly replace the function of a resilient bar joint. These anchoring and supporting elements can be used in symmetric residual den-titions for bilateral free-end saddle support (Figs 5-50 to 5-52). Limitation of movement is dened by a depth stop; spring bolts press the hinges back into their starting position on relief of loading.Limitation of movement becomes necessary to avoid overloading the mucosa and prevent framework components from becoming embed-ded. In the case of hinge joints without limitation of movement, extremely uneven mucosal stress-es arise; these components are unserviceable.Fig 5-52 Free-end saddles with jointed anchorage settle dis-tally into the mucosa. If the free-end saddle sinks distally, a sublingual bar is lifted mesially and presses against the alveolar ridge.Fig 5-50 Bilateral free-end saddles xed to the residual denti-tion with joints must not be joined together with a denture framework. This is because, in addition to parallelization within the path of insertion, this would require uprighting to a com-mon axis of rotation, which is not technically possible even in symmetric residual dentition situations.Fig 5-51 Bilaterally shortened dental arches should be tted with separate monoreducers if anchorage with joints is being attempted; the jointed attachments have to be lockable. 158Telescopic Anchoring and Supporting ElementsPassive and Active Retention AccessoriesTelescopic anchoring and supporting elements gain their dened retentive forces from adhesive and dynamic friction resistance (parallel and con-ical ttings) or from spring forces of activatable secondary parts (spreadable attachment blades or resilient bar sleeves). To protect the periodontal tissue and compensate for discrepancies in a par-allel t, additional intracoronal retention acces-sories can be used. These can be divided into (1) passive interlocking parts (locks or latches), such as turn-type locks, swivel-type locks, and sliding or push-type locks; and (2) active retentions, such as stud anchors and spring bolts. Locks and latches are passive retentions that are worked together with telescopic components (double crowns or bars). They can be cams, slid-ers, or bolts that swivel, slide, or turn. They t into the removable prosthesis and can be moved by the patient into a matching slot (keyway) or drill hole on a xed primary part in order to anchor the denture rmly.A turn-type lock is a twistable cam with an ec-centric slot (keyway) accommodated in the sec-ondary part (outer telescope). In the resting posi-tion, this cam wedges in a slot or drill hole on the primary part (inner telescope), and the pros-thesis is locked (Figs 5-53 and 5-54). If the cam is twisted, the telescopic crowns unlock, and the structure can be lifted off without stressing (ex-truding) the abutment tooth, as occurs with active retentive elements.A swivel-type lock is a horizontally tted swivel-ing slider that is located in the removable part of the denture and can be swiveled into a matching slot on the primary part of a telescopic anchoring component (Fig 5-55). A slide-type lock has a bolt in the removable secondary part, which is locked in a locking catch on the primary part (Fig 5-56). The bolt is guided horizontally and pressed into a locking position by means of a spring. When the matched parts are joined, the eccentric cam of the bolt slides over an inclined surface into the lock-ing catch. To unlock the device, the bolt can be de-pressed within its guide so that the eccentric cam slides out of the catch.A lock attachment is a spring-bolt lock that is integrated into a parallel attachment. This prefab-ricated anchoring and supporting element com-prises a at primary part with a T-prole with a cylindric locking slot recessed into a tting sur-face. A spring bolt engages in the slot and can be moved by a second, horizontally guided spring bolt. When the matched parts are joined, the rst spring bolt slides into the locking slot. To release, the rst spring bolt can be lifted out of the slot by the second, depressible spring bolt, and the par-allel attachment is separated (Fig 5-57). The advantage of locking mechanisms is that the dentures are absolutely rmly seated in their locked state and, after unlocking, can be removed without putting any stress on the abutment tooth. All forms of passive lockable retainers are avail-able as prefabricated components or as prefab-ricated sets with special tools, but they can also be made manually using dental technology tech-niques. The technical effort involved is consider-able, as is the space required by such components in telescopic anchoring and supporting elements. Locks are not easy to handle and should not be recommended for less dexterous patients.Active retention accessories are resilient com-ponents that can be accommodated in the outer crowns of telescopes or in bar components. In the case of resilient retention accessories, join-ing and separating forces have to be overcome, which can put stress on the periodontium. A spring-bolt anchor is preferably housed in the outer wall of a telescopic crown and has a spring-loaded bolt that engages in a slot on the primary part. A ball anchor consists of a metal ball in the outer telescope, which by means of a spring en-gages in a concave tting on the internal anchor. A stud anchor is made up of a cross-cut, spheri-cal, secondary part that engages in a double-conical drill hole. Stud anchors can be housed in bar stubs or rod-type bars and are only used in combination with telescopic supporting elements. 159Passive and Active Retention AccessoriesLatch pin openFig 5-57 The Robolock lock attachment from ZL Microdent is a rigid retentive element used for locking unilateral cantilever dentures and removable partial dentures. The screw-fastened guide sleeve of the lock can be inserted from both sides so that it can be used on the left and right. The denture is loosened from its anchorage by gentle pressure applied to the pin screwed into the side.Fig 5-53 Passive, lockable retainers include turn-type locks. A turnable cam (latch pin) is housed in the outer telescope. In the resting position, the latch pin engages in a slot on the inner telescope. To unlock, the pin is turned, and the structure can be lifted off.Fig 5-54 Interlocking between the primary and secondary crown by a turn-type lock is achieved by turning the latch pin 180 degrees.Fig 5-55 A swivel-type lock belongs to the group of passive, lockable retentive elements. The lock is housed in the outer telescope and can be swiveled around a pin or into a slot on the inner telescope. To unlock, the swivel arm can be twisted out-ward.Fig 5-56 With a slide-type lock, the bolt of the lock is pushed into the resting position by means of a spring. The lock slides over an inclined surface into the locking catch. To unlock, the bolt is manually depressed from the outside.Unlocked Turned 90 degrees Locked 160Telescopic Anchoring and Supporting ElementsPrefabricated AttachmentsT-attachments are simple, box-shaped attachments in which the matched parts have a rounded T-prole. The primary part often has a central ac-tivation slot that goes through to the bar, so that the sliding surfaces can be pushed apart and the attachments are activatable. Depending on size, they are suitable for placement within or outside the crowns. These rigid anchoring and supporting elements gain their retention from resistance to static friction.The multi-CON system (DeguDent) provides rigid anchoring and supporting elements where the at primary part can be positioned intracoro-nally and the secondary part is available in three different versions for different indications (Fig 5-58). The secondary part is made up of the T-shaped sliding prole, the activation body, and a retention bar that is engaged in a retention sleeve (Fig 5-59). The activation body runs either hori-zontally (multi-CON 90) for use with at alveolar ridges, or it is shifted in a basal direction for atro-phied alveolar ridges (multi-CON 1). The third ver-sion (multi-CON TR) is a at secondary part that cannot be activated or exchanged; it is used as a passive stress-breaker attachment for prospec-tive planning of restorations.In the case of the activatable secondary part, the activation screw engages in the activation body from the base and is able to push the sliding sur-faces apart in parallel, which means the joining and separating forces can be precisely measured.The primary part is supplied as a high-fusing prefabricated component for soldering or casting on as a spacer matrix or as an erosion electrode. The closed retention box has a basal, conical drill hole and can be soldered or bonded to the frame-work. In dovetail attachments, the sliding prole is triangular. These attachments can also be acti-vated via an activation slot in the secondary part. They are rigid and relatively sturdy attachments for anchoring free-end saddles. Generally speak-ing, dovetail attachments are used for interden-tal saddles and removable partial dentures and mounted intracoronally.The dovetail attachment according to Crismani can be integrated intracoronally (Fig 5-60). Both parts of the attachment are made from a high-fusing gold-platinum alloy for direct casting on with other gold-platinum alloys or for soldering in place. The secondary part is slotted throughout its length and is spread to activate it. The height of the attachment can be shortened to the required proportions; preparation must be done from the top down with the attachment parts put together.Roller attachments are connectors with limited rigidity for intracoronal and extracoronal place-ment. The cylindric component engages in an ac-tivatable sleeve open on one side.Fig 5-58 The design of the T-attachment in the multi-CON system is a double cylinder that can be spread over the activation body.Fig 5-59 The design of the DuoLock attachment is the same as that of the multi-CON attachment. Both have replaceable secondary parts. 161Prefabricated AttachmentsThe precision attachment from Degussa is a small, rigid, activatable roller attachment for re-movable partial dentures and xed partial den-tures (Fig 5-61). The secondary part has a spring blade in the gingival third, which means a cam can engage in the slot on the primary part.Degussa’s special attachment is a roller attach-ment that has limited rigidity (Fig 5-62). It com-prises a slotted sleeve and a roller with a bar ex-tension, which are supplied in gold-platinum and in high-fusing gold-platinum alloy. This special attachment is supplied in two thicknesses and is available in rod lengths of 50 mm for efcient working.The special attachment is suitable as an inter-lock attachment because the sleeve is placed ap-proximally between two abutment teeth with the roller acting as the secondary part. The roller can also be integrated with a connecting bar extra-coronally to the anchoring crowns as the primary part, while the sleeve is occlusally closed and xed in the removable restoration. Roller attach-ments are supplied in prefabricated proles and separated into suitable lengths. They are used as stress-breaker attachments because of their small dimensions.Articulated attachments are available in vari-ous designs; the most common is the Dolder bar joint. Other designs include the FM hinge joint (Figs 5-63 and 5-64) and the Ancorvis hinge stress breaker (both from Degussa). These articulated attachments are not suitable for simultaneous bi-lateral use but for unilateral use only.Fig 5-60 The closed, activatable dovetail attachment is used with a circular notch and shear distributor.Fig 5-61 The precision attachment from Degussa is a small, closed, and activat-able roller attachment.Fig 5-62 The special attachment is a simple, open roller attachment that can be activated to a limited extent.Primary partSecondary partHinge axisCoil springSpring boltLocking screwFig 5-63 The FM hinge joint is used for unilateral free-end saddles with two or three teeth (monoreducer); bilateral free-end saddles must not be joined transversally. Rotary move-ment is limited by a stop. On loading of the free-end saddle, a hinge movement presses the spring bolt back into its guide; when loading ends, the spring bolt returns the free-end saddle to its initial position.Fig 5-64 Components of the FM hinge: Both parts of the joint are directed horizontally by a parallel guide. When the parts of the joint are joined, the spring bolt engages in a slot on the primary part, and both parts lock. Coil springs and spring bolts are replaceable. 162Telescopic Anchoring and Supporting ElementsRoot Crown AnchorsRoot crown anchors are prefabricated anchoring components that are placed onto root pin crowns. They are used to anchor hybrid prostheses.Root crown anchors for hybrid dentures are prefabricated systems comprising sleeve and cyl-inder, annular spring and spring sleeve, or press-stud as well as bar systems. These anchoring sys-tems are designed for placement on root crowns. If a rigid connection is intended, several anchors are placed in one jaw because rotary movements occur around the vertical axis. Root crown an-chors are supplied as partly rigid or resilient an-chors (Figs 5-65 and 5-66). Retention is achieved by static friction and resilient restraints (Figs 5-67 and 5-68). The anchorage according to Rother-mann (Degussa), the Dalbo anchor (Degussa), the retention cylinder by Gerber, and the Dolder bar are examples.The Rothermann anchorage system is a form of root crown anchorage that can be used as a rigid and a resilient connector. The primary part con-sists of a at cylinder with a circular channel into which the secondary part engages in the form of an open spring clip. The secondary part has sad-dle retentions for integration into the plastic base. The at design means it can be used in situations with very limited space.Dalbo anchors are press-stud–like anchoring el-ements in which the primary part is a small cylin-der stub or a ball-head, and these are tted onto root crowns. The secondary part is an activatable sleeve with four slots, which is polymerized into the denture base. They are resilient root crown an-chors for partial and hybrid prostheses. The Dalbo cylinder is rigid in the horizontal plane and per-mits vertical and rotary movements. The blades of the secondary part engage over the spherical or cylindric primary part and can be pressed inward to be activated. During assembly, a polyvinyl chloride ring is pushed over the secondary part; it is polymerized into the acrylic resin base and re-mains in the nished denture. In addition, during assembly the supplied tin disc is incorporated as a spacer between the two parts of the attachment to create the resilience leeway. The Dalbo anchor with a ball-head (Degussa ball-anchor system) has only limited rigidity, even when it is used in combination with several single anchors.The Gerber retention cylinder is a root crown anchor for removable partial dentures or xed partial dentures as well as overdentures. The pri-mary part, the retention core, is a replaceable cyl-inder pin with a ring groove; an annular spring that is open on one side and integrated into the secondary part engages in this groove. The reten-tion core is screwed onto a solder base for the root crown. The secondary part is a sleeve hous-ing with retentive surfaces for anchoring in the denture acrylic resin. The annular spring located in the housing of the secondary part snaps into the ring groove on the retention core when the parts of the anchor are joined together. The re-placeable annular spring is held in the sleeve housing with a threaded ring.The root crown to receive anchors is xed in a prepared root canal of the abutment tooth with a root (endodontic) pin. Preparation of the root is based on the described principles for pin anchor-age in devitalized teeth, with circular enclosure of the root and auxiliary cavity. The root crown satises periodontal hygiene requirements and must not cause mechanical irritation to the mar-ginal periodontium. It covers the root prepara-tion as far as the gingival crevice and allows the denture base to engage bodily if rigid anchorage is the aim. For this purpose, the crown surface is made smooth and sharp-edged and has a circular chamfer; the crown walls are slightly tapered. Table 5-1 outlines the various functions, hygiene considerations, reparability, and indications for different telescopic components. 163Root Crown AnchorsLRLRFig 5-66 If two canine root preparations are used for support, the horizontal position is secured; vertical position is secured via two supports: the mucosal support and the periodontal tis-sues of the canines. This structure can be successful for de-cades if encapsulation of the marginal periodontium is offset by rigorous oral hygiene.Fig 5-65 Quasi-complete dentures can be anchored onto root preparations tted with root crowns; the root preparations are fully covered by the denture. These structures are known as hybrid prostheses or overdentures. Anchorage can be achieved with ball anchors and resilient sleeves. The anchorage compo-nents have resilience leeway (LR) that relieves the root prepara-tions.Fig 5-68 Lever relationships that consist of a force arm (A) on a telescopic crown and a work arm (C) in the root area are far less favorable with a telescopic crown.Fig 5-67 Support on root crowns with ball anchors or bars has static advantages: The force exerted (F1) acts on the denture with a lever arm (A) on the denture rest area and the movable connection at the root crown. At the root crown, the force (F2) acts with the force arm (B) at the fulcrum, which is far shorter than the load arm (C) in the root area.F1AF2CBF1AC 164Telescopic Anchoring and Supporting ElementsTable 5-1 Telescopic componentsComponentSupporting function of the securing horizontalAnchoring function of the dened retentive forcePeriodontal hygiene and cleanability Handling and reparability Indications and affordabilityTelescopic crown:• Parallel-guided double crown• Fixed inner crown• Removable outer telescope• Tooth-colored veneerRigid connecting element:• Absolutely secures the horizontal and vertical position• Secures supporting function• In a group, they provide very good splinting of abutmentsMatched parts anchor by means of static and dynamic friction:• Retention is not calculable• Retention is dependent on:– Fitting tolerances– Surface quality– Size of contact surfacesDouble-walled crowns:• Have large space requirement• Because of anatomical tooth shape, they have surface bulges conducive to periodontal hygiene• Plaque accumulation possible in tting gaps and additional retainersBest handling for patients:• Can be readily inserted• Adequate accuracy of t• Subsequent incorporation of friction plugs if retention is poor• Minimal reparability• Retentive elements can be replacedBroad range of uses:• Used for xed and removable partial dentures • Teeth are substantially prepared• Cannot be used in teeth with a large pulp cavity• Medium life span• Sufciently economicalConical crown:• Double crown with conical tting surfaces• Fixed inner crown• Removable outer crown• Tooth-colored veneerRigid anchoring and supporting element:• Firmly secures the horizontal and vertical position• Secures supporting function• In a group, they provide very good splinting of abutmentsMatched parts are retained by means of static friction in the nal position:• Retention is dened and can be deter-mined in advance due to:– Variable taper angle– Joining forceConical crowns:• Have medium space requirement• Are very good for periodontal hygiene because of anatomical surface bulges• Result in no plaque accumulation in tting gapsGood handling for patients:• Easy to use• Good accuracy of t• High joining forces lead to wedging with very high separating forces• Minimal reparability• Cannot be replacedUniversal use:• Used for xed and removable partial dentures • When used in a group, the residual dentition is splinted• Cannot be used in teeth with a large pulp cavity• Medium life span• EconomicalCircular notch with shear distributor:• Parallel guidance on lingual wall of crown• Approximal nishing groove• Cervical shoulderStabilizing element with cervical shoulder:• Secures the vertical position very well• Secures the horizontal position only in interaction with combined attachment• With a stud anchor, rigid coupling is not possibleNo inherent retentive forces:• Only in conjunction with anchoring elements such as:– Stud anchors– Activatable attachmentsShear distribution arms:• Sunk into the crown wall• Have surface bulges conducive to periodontal hygiene• Plaque accumulation is possible in tting gaps• In case of press-stud anchorage, mucosal irritation could occur in the tooth-denture interfaceGood handling for patients:• Offers good guidance for prefabricated attachment• Not reparable• Cannot be replacedUniversal use:• Used for xed partial dentures• Used for teeth undergoing substantial corrective reduction• Cannot be used in teeth with a large pulp cavity• Medium life span (approximately 6 years)• Sufciently economicalDuoLock attachment:• Rigid parallel attachment• Secondary part a double cylinder• Flat primary partRigid connecting elements:• For rigid coupling• Closed attachment• For periodontal support• Extended proximal bars protect against rotation and tipping• Lingual circular notch is necessaryDened retentive forces due to the following:• Spring blades can be activated to a dened extent• Slotted bar is spread with conical activation screwPrimary parts are at: • Flat surface allows for intracoronal integration• Primary part covers marginal periodon-tium slightly• Secondary part has gingival contact• No encapsulation spaces• Good cleanability• Satisfactory in terms of periodontal hygieneHandling is problematic:• If circular notch is present, handling is good• Very good accuracy of t• Activatable for permanent retentive forces• Worn parts are replaceable• Very good reparabilityUniversal use:• Used for partial cantilever and inter-dental dentures• Can be integrated with all full crowns• Used in anterior area• Bonded, soldered, and cast on• Long life span• Very economical• Technical fabrication is straightforwardMulti-CON system:• Rigid T-attachment• Flat primary part• Secondary part in three versionsRigid connecting elements:• Closed attachment• For periodontal support• With lingual circular notch, provides absolutely rigid coupling and securing of horizontal positionDened joining and separating forces:• This occurs because of spring blades that can be activated to a dened extent• Basal activation screw pushes sliding surfaces apart in parallelPrimary part is at:• Flat surface allows for intracoronal integration• Activation body in the secondary part runs horizontally or is displaced basally• Has gingival contact• No encapsulation spaces• Safe in terms of periodontal hygieneHandling is good:• But only with circular notch• Very good accuracy of t• Activatable for permanent retentive forces• Worn parts are replaceable• Very good reparabilityUniversal use:• Used for dentures and prospective planning as stress-breaker attachment• Used for at, atrophied alveolar ridges• Bonded, soldered, and cast on• Spacer technique, erosion technique• Very long life span• Economical 165Root Crown AnchorsTable 5-1 Telescopic componentsComponentSupporting function of the securing horizontalAnchoring function of the dened retentive forcePeriodontal hygiene and cleanability Handling and reparability Indications and affordabilityTelescopic crown:• Parallel-guided double crown• Fixed inner crown• Removable outer telescope• Tooth-colored veneerRigid connecting element:• Absolutely secures the horizontal and vertical position• Secures supporting function• In a group, they provide very good splinting of abutmentsMatched parts anchor by means of static and dynamic friction:• Retention is not calculable• Retention is dependent on:– Fitting tolerances– Surface quality– Size of contact surfacesDouble-walled crowns:• Have large space requirement• Because of anatomical tooth shape, they have surface bulges conducive to periodontal hygiene• Plaque accumulation possible in tting gaps and additional retainersBest handling for patients:• Can be readily inserted• Adequate accuracy of t• Subsequent incorporation of friction plugs if retention is poor• Minimal reparability• Retentive elements can be replacedBroad range of uses:• Used for xed and removable partial dentures • Teeth are substantially prepared• Cannot be used in teeth with a large pulp cavity• Medium life span• Sufciently economicalConical crown:• Double crown with conical tting surfaces• Fixed inner crown• Removable outer crown• Tooth-colored veneerRigid anchoring and supporting element:• Firmly secures the horizontal and vertical position• Secures supporting function• In a group, they provide very good splinting of abutmentsMatched parts are retained by means of static friction in the nal position:• Retention is dened and can be deter-mined in advance due to:– Variable taper angle– Joining forceConical crowns:• Have medium space requirement• Are very good for periodontal hygiene because of anatomical surface bulges• Result in no plaque accumulation in tting gapsGood handling for patients:• Easy to use• Good accuracy of t• High joining forces lead to wedging with very high separating forces• Minimal reparability• Cannot be replacedUniversal use:• Used for xed and removable partial dentures • When used in a group, the residual dentition is splinted• Cannot be used in teeth with a large pulp cavity• Medium life span• EconomicalCircular notch with shear distributor:• Parallel guidance on lingual wall of crown• Approximal nishing groove• Cervical shoulderStabilizing element with cervical shoulder:• Secures the vertical position very well• Secures the horizontal position only in interaction with combined attachment• With a stud anchor, rigid coupling is not possibleNo inherent retentive forces:• Only in conjunction with anchoring elements such as:– Stud anchors– Activatable attachmentsShear distribution arms:• Sunk into the crown wall• Have surface bulges conducive to periodontal hygiene• Plaque accumulation is possible in tting gaps• In case of press-stud anchorage, mucosal irritation could occur in the tooth-denture interfaceGood handling for patients:• Offers good guidance for prefabricated attachment• Not reparable• Cannot be replacedUniversal use:• Used for xed partial dentures• Used for teeth undergoing substantial corrective reduction• Cannot be used in teeth with a large pulp cavity• Medium life span (approximately 6 years)• Sufciently economicalDuoLock attachment:• Rigid parallel attachment• Secondary part a double cylinder• Flat primary partRigid connecting elements:• For rigid coupling• Closed attachment• For periodontal support• Extended proximal bars protect against rotation and tipping• Lingual circular notch is necessaryDened retentive forces due to the following:• Spring blades can be activated to a dened extent• Slotted bar is spread with conical activation screwPrimary parts are at: • Flat surface allows for intracoronal integration• Primary part covers marginal periodon-tium slightly• Secondary part has gingival contact• No encapsulation spaces• Good cleanability• Satisfactory in terms of periodontal hygieneHandling is problematic:• If circular notch is present, handling is good• Very good accuracy of t• Activatable for permanent retentive forces• Worn parts are replaceable• Very good reparabilityUniversal use:• Used for partial cantilever and inter-dental dentures• Can be integrated with all full crowns• Used in anterior area• Bonded, soldered, and cast on• Long life span• Very economical• Technical fabrication is straightforwardMulti-CON system:• Rigid T-attachment• Flat primary part• Secondary part in three versionsRigid connecting elements:• Closed attachment• For periodontal support• With lingual circular notch, provides absolutely rigid coupling and securing of horizontal positionDened joining and separating forces:• This occurs because of spring blades that can be activated to a dened extent• Basal activation screw pushes sliding surfaces apart in parallelPrimary part is at:• Flat surface allows for intracoronal integration• Activation body in the secondary part runs horizontally or is displaced basally• Has gingival contact• No encapsulation spaces• Safe in terms of periodontal hygieneHandling is good:• But only with circular notch• Very good accuracy of t• Activatable for permanent retentive forces• Worn parts are replaceable• Very good reparabilityUniversal use:• Used for dentures and prospective planning as stress-breaker attachment• Used for at, atrophied alveolar ridges• Bonded, soldered, and cast on• Spacer technique, erosion technique• Very long life span• Economical 166Telescopic Anchoring and Supporting ElementsProcessing Prefabricated AttachmentsFollowing are the steps for processing a prefabri-cated attachment tting (Fig 5-69): 1. Crown frameworks are waxed up and, if nec-essary, given a circular notch for a shear dis-tributor. 2. In a parallelometer, the primary part is inte-grated into the crown frameworks with a par-alleling mandrel. 3. Integration can be done by:• Soldering the component into a recess in the crown framework• Casting on; joining together directly with al-loys that can be cast on• Bonding into a recess in the crown frame-work• Using a spacer technique with a shaped spacer• Spark erosion with a forming electrode 4. The primary part is captured with modeling wax over the entire length at a minimum layer thickness of 0.3 mm. 5. One of the following is done to the wax crown framework:• It is invested with the waxed-in component for the casting-on process.• The component is removed from the wax template so it can later be soldered or bond-ed in place.• It is invested with the spacer. 6. After casting, the crown framework is nished; if the component is to be soldered or bonded, the recess/spacer sleeve is cleaned (airborne-particle abraded). The edges of the recess are beveled slightly. For soldering, a notch is milled into the lingual side wall. 7. Components are shortened to the occlusion level. It is important to check beforehand whether the remaining attachment surface is still adequate. The secondary part is also short-ened to the occlusion level. 8. A duplicating aid is then inserted, on which the retention sleeve for the secondary part sits. 9. The retention sleeve (or the secondary part) can also be cast on, soldered on, bonded, or directly xed in the denture acrylic resin. 10. The denture framework with the shear distri-bution arm is modeled on an investment cast in the model casting technique, encompass-ing the retention sleeve. 11. After casting, airborne-particle abrasion, and nishing, the retention sleeve is xed using the chosen method and the secondary part is screwed in place.Prefabricated attachments consist of the prima-ry part, which is known as the matrix irrespective of its geometric shape, and the secondary part, which by analogy is called the patrix. Primary parts are supplied in different alloys for casting on, soldering on, or bonding; they are available as spacer matrices or as erosion electrodes. The parts supplied include modeling parts made of plastic as primary part spacers for the soldering and bonding techniques, as well as cast-on spac-er sleeves for the soldering technique. Secondary parts have multiple components and comprise the patrix, the retention sleeve, and the activation and retention screws. For model casting fabrica-tion, duplicating aids and modeling patrices with retention sleeves are available.The special tool kit contains a torque screw-driver with blade insert, the patrix holder, a screwdriver for activation, retention screws, and a carbon splint as a xing aid for soldering model fabrication. 167Processing Prefabricated AttachmentsFig 5-69 Basic procedure for processing a prefabricated attachment tting. (a) The crown framework is waxed up in casting wax and, if necessary, given a circular notch. (b) The attachment part is positioned parallel to the circular notch with the parallelometer. Methods for doing this include recess for soldering, casting-on technique, spacer technique, or spark erosion. (c) So that the pri-mary part can later be soldered in place, a recess is created or a cast-on spacer is modeled in. (d) The recess for soldering is pre-pared: The edges are beveled, and a small notch to receive the solder is milled. (e) The attachment is inserted with the parallelom-eter, xed with sticky wax, and soldered onto a soldering model. (f) The attachment is shortened occlusally, and the secondary part with the retention sleeve is inserted and prepared for model casting. The denture framework embraces the retention sleeve and forms the shear distributor. (g) The retention sleeves of the secondary parts are usually bonded in place; cast-on retention sleeves can be invested at the same time in the casting-on technique. (h) The secondary part is screwed in and, together with the shear distributor, must be capable of being joined and separated smoothly. abc d ef g h(cont on next page) 168Telescopic Anchoring and Supporting ElementsFig 5-69 (cont) (i) Cast-on attachment parts are tted into place in the parallelometer and modeled into the crown framework. (j) Cast-on attachment parts made of high-fusing alloys are invested at the same time. (k) For bonding the primary part in place, a cast-on spacer is waxed in; the spacer protrudes above the wax-up for xation in the investment material. (l) The attachment part is tted into place after casting and bonded into the nished crown framework with the aid of the parallelometer. (m) The spacer is made of ceramic; with the shaft part, it is clamped into the parallelometer and modeled into the crown framework. (n) The shaft part of the spacer is unclamped, trimmed with a diamond separating disk, and invested with the crown framework. (o) After casting, the spacer is airborne-particle abraded with glass or plastic beads at 2 bars; the secondary part is tted into place.i j kl m no 169Integrating Prefabricated ComponentsIntegrating Prefabricated ComponentsSoldering, the most common method of joining components, is multipurpose and easy to use. Soldering involves joining metallic materials in their solid state by means of an added molten ma-terial. At working temperature, the solder ows into a narrow solder gap and completely lls it. The melting temperature of the solder is slightly below the solidus temperature of the basic mate-rial, and diffusion causes the solder to mix with the alloy in the border area (diffusion zone) of the solder gap. The following requirements must be met for the diffusion zone to form:• The working temperature of the solder is matched to the alloy.• The composition of alloy and solder are matched.• The oxide layer is prevented by ux.• The surfaces being soldered should be rough-ened.• Narrow parallel solder gaps should be shaped to use capillary action.For soldering, the component is positioned in the parallelometer with a paralleling mandrel and xed into the recess created on the crown frame-work. In the soldering model, the component is xed with a carbon splint. The solder gap and milled notch for placing the solder must be read-ily accessible.Casting on is a method of joining components in which a solid material is wetted with a liquid alloy during casting. Unlike soldering, the second component being attached is liquid when melted onto the rst component. The molten mass must increase the temperature of the cast-on part so much that a diffusion zone is formed in the solid cast-on material and a metallic join is created. The recommendations for casting on include the fol-lowing:• Only use special cast-on alloys.• The melting range of the cast-on alloy must be higher than that of the molten alloy.• The cast-on part should be preheated to work-ing temperature.• The cast-on alloys do not form an oxide layer during preheating.If the solidus point of the cast-on alloy and cast-ing temperature are too close, hot molten mate-rial may penetrate the thin walls of the cast-on parts. As a result of expansion differences be-tween the investment material and cast-on part during preheating and casting, gaps may arise between the investment and the cast-on part, and the liquid alloy may run into the cast-on part. If the coefcients of expansion differ between the casting alloys and cast-on part, the cast-on com-ponents may deform as they cool, and casting stresses may cause the component to separate or shift its position.The spacer technique is a combination of sol-dering and casting on, which can compensate for processing difculties during casting on. For in-tracoronally placed components, a spacer sleeve made from castable alloy is used. The spacer is di-mensioned so that, after casting on, slight chang-es to the position of the primary part can be made before it is soldered in place; casting stresses af-fecting the spacer that are caused by casting on can thus be compensated for.The bonding technique for joining components in crown and denture frameworks replaces sol-dering or casting on. The surfaces of the compo-nents to be bonded are airborne-particle abraded with alumina and coated with adhesive. The syn-thetic dual-component adhesives (powder/liq-uid or paste/paste) are organic compounds that set when cold as a result of chemical reactions, or setting is triggered and accelerated by expo-sure to light. The specially developed adhesives are biocompatible and dimensionally stable up to 120°C so that hot-curing denture acrylic resins can be used.The spacer technique is a method for fabricat-ing a primary tting part of an attachment with the aid of a molded part (spacer). The spacer re-tains space in the shape of the secondary part; it is made of alumina and has an extremely smooth surface and a high melting point (2,045°C). The spacer is integrated into the wax template of the anchoring crown and invested with the crown wax-up. The casting metal is cast directly onto the spacer, which is then airborne-particle abraded to create the appropriate tting surface in the an-choring crown. 170Telescopic Anchoring and Supporting ElementsThe procedure starts with waxing up of the crown frameworks, in which a circular notch is created. Once the blades (lamellae) of the spacer have been coated with a thin layer of modeling wax, the spacer shaft can be clamped in the paral-leling mandrel in order to place the lamellar part intracoronally in the crown framework in the path of insertion. The circular notch is taken up to the spacer. The spacer shaft is then unclamped and separated at its marking with a diamond separat-ing disc so that part of the spacer protrudes out of the wax template to provide retention in the investment material.Investing and casting are performed as usual. Expansion of the investment material has no in-uence on the size of tting surfaces after casting. After casting, the spacer can be blasted out of the cast part with glass or plastic beads at a maxi-mum of 2 bars.Spark erosion is a processing method in which the material is removed by means of electric arcs or periodic spark discharges between the tool (negative electrode) and the workpiece (positive electrode), whereby both parts are separated by a nonconductive working medium known as the dielectric. The electrode has the negative shape of the primary tting part. As a result of the discharge processes, the material particles are removed by melting and vaporizing and ushed away by the dielectric. In dental technology, specially shaped graphite and copper electrodes are used to erode very accurate shapes of tting surfaces for attach-ments, bars, grooves, and locks.Fabricating a Three-Unit Partial Denture and Inner TelescopeFigure 5-70 diagrams important considerations regarding fabrication of the partial denture and inner telescope, and Figs 5-71 to 5-73 diagram the error analysis considerations. The steps for fabrication of the three-unit partial denture are as follows:1. Fabricating the milling base (Fig 5-74)2. Waxing up the telescope (Fig 5-75)3. Waxing up the partial denture (Fig 5-76)4. Casting and tting on the cast objects (Fig 5-77)5. Ceramic veneering (Fig 5-78)6. Finishing the milled work and polishing (Fig 5-79) 171Incisal edge• Thick/voluminous in incisal area• Tapers thinly downwardDentin• Central mass; apply thick/voluminous layer• Tapers thinly in cervical direction• Cutting edge, wedge-shaped/jagged layering (shape the mamelons)Metal framework• No oxide ring required with nonprecious metal• In mass ring, enough adhesive oxides• Possible wash ring to highlight contaminants (and eradicate them)Opaque• Opaque layering and ringsOpaque dentin for darker cervical coloringFabricating a Three-Unit Partial Denture and Inner TelescopeEnamel ridges, white coloringIncisal cutting edge (mesial and distal), bluishEnamel crack, dark brownCervical neck, yellow-orangeChalk spot, whiteOcclusal shoulder milling to the attachment• Needs a smooth transition for the attachment to be covered by the denture framework• Hygienic sealStabilizing groove• Adequate width and depth• Smooth surfaceOcclusal shoulder milling to the stabilizing groove• Provides a smooth transition for the denture frameworkOcclusal shoulder milling• Uniform width (approximately 0.2 mm)• Angled transition to the occlusal surfaceCervical shoulder milling• Approximately 0.5 to 0.8 mm wide• Not overhanging the periodontiumTransition from stabilizing groove to pontic• Must not reduce the connection between the pontic and the crownFig 5-71 Error analysis facts found in this occlusal view of a circular notch.Fig 5-70 Important considerations re-garding color and fabrication of the partial denture and inner telescope. 172Telescopic Anchoring and Supporting ElementsOcclusal surface• Smooth or rudimentary reproduction of the shape of the occlusal surface• Surface polished• Adequate freeway space for wall thickness of an outer telescope (minimum of 1 mm)Occlusal bevel• Evenly slanting transition to the milled sur-faces, approximately 45 degrees, smooth• Allows better handling by the patientHeight of milled surfaces• Minimum of half the crown height• Achieve minimum height in a circle• Measured from the chamfer to the occlusal bevelParallelism of milled surfaces• Encircling parallelism (minimum of two facing surfaces)Surface quality of milled surfaces• No chatter marks, scratches, or grooves• Lap with milling oil. Do not polish!Preparation/preparation margin accuracy of t• No marginal gap, no overlapping• Inner telescope must not wobbleInside of crown• Smooth, evenly worked with airborne- particle abrasion polisher• No wax-ow lines• No hole in the crownCrown wall thickness• In the area of milled surfaces, 0.3 to 0.8 mm• Crown wall is closedPath of cervical shoulder milling• Even path•Encircling• Uniform distance from the gingival marginWidth of cervical shoulder milling•Approximately 0.3 mm wide• Not overhanging the periodontium• Sharp-edged transition to the wall of the crown marginCrown margin shaping• Uniform thickness• Matches the chamfer preparation• No phase marginFig 5-72 Error analysis facts found for an inner telescope.Fig 5-73 Error analysis facts found for a circular notch.Attachment, circular notch, stabilizing groove• Run parallel within the path of insertion• Lie at roughly the same height• Approximately half the crown heightCervical shoulder milling• Follows even path• Roughly parallel to the gingival margin• Smooth transition to the groove and attachmentPrefabricated attachment• Intracoronal placement with smooth shape transitions to the circular notch and shoulder millingSurfaces of stabilizing groove and circular notch• Smooth (do not polish, but lap) without chatter marks, scratches, or grooves 173Fabricating a Three-Unit Partial Denture and Inner TelescopeSawn, sectioned model• Set up on the milling machine in the model holder.• Determine the path of insertion with a surveying rod.• Allow for the position of attachment, stabilizing groove, and telescope; pay attention to wall thicknesses.• Ensure slight mesial tipping.• The attachment lies cervically on the die.• The stabilizing groove is set back cervically from the die.• The telescope has uniform wall thickness.Transfer spider• Insert and establish a depth stop on the milling machine.• Bring the transfer spider in contact with all the dies.• Stably x the dies onto the transfer spider with sticky wax.• Magnetically establish the swivel arm and model holder.Die segments• First detach swivel arm, then the depth stop.• Carefully extract die segments from the model base.• Spray dies with plaster isolating agent and leave to dry.• Handle everything with great care because of the risk of fracture.Depth stop• Locate the depth stop on the milling machine for the milling base.• Use a glass plate to provide an absolutely at surface.• For better hold during remilling, work with magnetic adhesive disc or magnetic auxiliary molds.• Fabricate the base to be as at and broad as possible to ensure stability.Milling base• Place the correct amount of base plaster on a glass plate or mold.• Fix the swivel arm of the milling machine.• Lower the isolated dies into the plaster to the depth stop and leave to set.• Do not embed dies too deeply in the base plaster.• Ensure adequate xation and stability.Fig 5-74 Fabricating the milling base. (a) Set up the sawn, sectioned model. (b) Insert the transfer spider. (c) Lift out the die segments. (d) Locate the depth stop. (e) Shape the milling base.abcde 174Telescopic Anchoring and Supporting ElementsUnderlining foils• Heat up the underlining and spacer foil.• Press the die into the foil/modeling material.• After cooling, extract the die.• Cut off foil 1 mm above the preparation margin.• Take out spacer foils and mark out the crown margin.• Immerse the coping.• Pay attention to wax temperature.• Withdraw steadily from the wax bath.Red cervical wax• Thinly place a warning layer over the wax or acrylic resin coping (to indicate minimum thickness when milling in wax).• Generously apply milling wax to create the shape of the eventual milled surfaces.• Apply cervical wax at the crown margin.• Apply a thin layer of wax to the occlusal surface.• Pay attention to freeway space.• Create the rudimentary shape of occlusal surfaces.Parallel milling• Uniformly adjust the height of the milling surfaces (half the crown height).• Remill wax until smooth (with a spiral wax cutter or sharp blade and at a low speed).• Mill the cervical shoulder to 0.3 mm wide.• The occlusal bevel should be approximately 45 degrees and 1.5 mm wide.Occlusal surface• Shape until smooth; possibly create an occlusal contour of the die.• Check for adequate freeway space (at least 1.5 mm from the antagonist).• Check surfaces externally and internally.• Flood with matt glaze to render smooth and clean.• Attach a 3-mm sprue to the occlusal surface in the direc-tion of the ow of molten material without any volume change in the sprue.Milling surfaces• Take up a suitable wax cutter (3-mm diameter).• Do not create chatter marks or grooves in wax.• Pay attention to wall thickness: ➙ A red warning layer is visible in the cervical wax. ➙ Check with a wax gauge (maximum of 0.6 mm).• Cervical shoulder milling follows a gingival course.• There is a sharp-edged transition to the crown margin.• The crown margin is uniformly thin to protect the marginal periodontium.Fig 5-75 Waxing up the telescope. (a) Draw the underlining foils. (b) Place warning layer. (c) Premill the milling sur-faces. (d) Mill around the milling surfaces in parallel. (e) Create an occlusal surface.abcde 175Fabricating a Three-Unit Partial Denture and Inner TelescopeFig 5-76 Waxing up the partial denture. (a) Reinforce the coping. (b) Wax up the pontic. (c) Wax up the cusp tips and ridges. (d) Wax up the vestibular and occlusal surfaces. (e) Create space for the attachment. (cont on next page)Reinforcing the coping• Flood on modeling wax (uniformly about 0.5 mm thick).• Utilize the transparency of the wax.• Cervically create the metal margin (channel-shaped for metal-ceramic).• Distally build up the join to the adjacent tooth (which is not veneered cervically with ceramic).• Smooth veneer surface and wax edges.Pontic wax-up• Place wax wire in the shape of the tooth.• Create stable connection points.• Ensure rinsability in the interdental space.• The pontic is in a reduced premolar shape (for uniform ceramic layer thickness).• Pay attention to length gingivally and buccally.• Shape veneer surfaces until convex and smooth.• Create a channel-shaped rim at the metal-ceramic junction.Cusp tip wax-up• Wax-up starts with dening the cusp tips.• Next, wax up cusp ridges mesially and distally.• Establish size and position of the occlusal surface in relation to tooth shape.• Place antagonist contacts on the marginal ridge.Occlusal wax-up• Shape cusp slopes and medial ridges.• Pay attention to dimension buccally and cervically.• Build up marginal ridges convexly.• Fill ssures on the vestibular surface.• Draw in the tooth neck in the approximal cervical area.• Shape the lingual and buccal cusp crests to form the antagonist contact.• Create triangular ridges with supplemental grooves with-out contact; pay attention to anatomical tooth shape.Space for attachment• Mark distance from the attachment to the gingiva in the cervical area.• Create space for positioning the attachment in the cervi-cal area.• For acrylic resin copings, carve a window beforehand.• The die must shine through the wax pattern.abcde 176Telescopic Anchoring and Supporting ElementsPlacement• Integrate the attachment into the wax pattern intercoronally on the attachment holder.• Align the attachment with the middle of the alveolar ridge.• Ensure that there is no mucosal contact (stay clear of the periodontium).• Fix with very hot wax.• Fill up the inside of the crown.• Do not ood the tting surfaces.• Twist open attachment holder and start up the milling machine.• Trim the attachment in metal.Circular notch• Mill a U-shaped circular notch in wax.• Create a cervical shoulder milling 0.3 mm wide (as a hygienic seal and channel-shaped around the attachment, circular notch, and stabilizing groove).• The occlusal shoulder should be 1.5 mm wide (if static support) to absorb axial forces.• Excavate the stabilizing groove with a thin cutter opposite the attachment.Separation• Separate the partial denture with sewing thread (and remove wax clamps).• Guide the sewing thread carefully like a bandsaw.• Shape the pontic to be smooth and convex at the base, without mucosal contact.• Check cervical-interdental rinsability.• Join separated partial denture segments on the model base (with wax or adhesive).Sprues• Attach the sprues to the partial denture pontics at the thickest part.• Ensure a crossbeam 4 to 5 mm thick in the partial denture.• Attach the sprues to the partial denture: diameter 2.0 to 2.5 mm (3.0 mm for thick pontics).• The distance from the beam should be approximately 3 mm.• The distance from the sprues to the crossbeam should be approximately 3.5 mm.• Shape all transitions to be smooth and clean (otherwise investment material may chip during casting).Placement in casting ask• Lift the partial denture very carefully off the model (risk of warping).• Place the partial denture outside the heat center toward the outer wall.• The crossbeam should lie in the center.• The crown edges should show outward.• The safety distance from the casting ask liner is 3 to 4 mm.• The safety distance from the top is approximately 4 to 5 mm.fghijFig 5-76 (cont) (f) Place the attachment. (g) Mill the circular notch. (h) Separate the partial denture. (i) Sprue and merge the partial denture together. (j) Place the partial denture in the casting ask. 177Fabricating a Three-Unit Partial Denture and Inner TelescopeInvesting• Mix the investment material according to the manufac-turer’s instructions.• Brush the attachment, stabilizing groove, occlusal surfaces, and inside of the crown.• Quickly pour in the remaining material without bubbles.• If possible, perform pressure investment (usually 20 minutes).Casting asks• Follow the instructions of the investment material manu-facturer.• Use the in-speed technique or conventionally bring the casting asks to their precise preheating temperature.• Roughen/dry-trim the ask lid for better water circulation when speeding the casting asks.• Strictly adhere to holding times and preheating tempera-ture according to instructions from the alloy and invest-ment manufacturers.Casting• Set up the casting unit, making sure it is technically okay and clean.• After preheating the casting asks, preheat the alloy in the casting unit, quickly load asks into the casting unit, and continue melting the alloy.• Cast nonprecious metal for 3 seconds after the shadow falling on the molten metal has broken up. • Remove casting asks and cool to room temperature.• Deask without knocking on the casting buttons.Fitting• First remove the oxide residues completely.• Fit each crown individually onto the die.• Watch for casting beads and excessively waxed-up crown margins, removing any.• Create a precise t with slight friction on the plaster dies.• Then fully set up the partial denture.• Check that there is no rocking and possibly separate, solder, or laser the partial denture.Corrective reduction• Prepare the sprues and machine out the shape.• Trim the attachment: ➙ Adjust the occlusion in the articulator. ➙ Check all contacts with articulating paper. ➙ Ensure that the attachment has space occlusally for the tertiary structure. ➙ Ensure a minimum 1-mm space from antagonists.Fig 5-77 Casting and tting on the cast objects. (a) Invest the cast objects. (b) Set up the casting asks. (c) Cast the cast objects. (d) Fit on the framework. (e) Perform corrective reduction of the occlusion.abcde 178Telescopic Anchoring and Supporting ElementsFramework• Prepare the metal surface for ceramic.• Make it thin at the margins (0.3 mm) with a smooth surface and open porosities.• Do not “rivet” in case of blunt grinding tools.• Do not introduce any foreign bodies.• Use sharp cutters/suitable stones.• Roughen/clean the surface with airborne-particle abrasion.• Be careful with abrasion pressures at crown margins (do not use circulation unit).Oxide ring• Carry out oxide ring.• For nonprecious metal alloys, perform as cleaning ring to get rid of contaminants (base alloy constituents form sufcient adhesive oxides during rings).• If metal surface appears unremarkable and homogenous, airborne-particle abrade oxides again.• Perform corrective reduction of noticeable features and airborne-particle abrade.Opaquer• Apply the opaquer thinly but in uniform thickness in two rings.• Possibly carry out a third opaque ring or use a bonder in advance.• Follow the ring instructions of the ceramic manufac-turer.Dentin material• Layer the dentin material in the shape of the tooth: ➙ Evenly without air bubbles, and not too wet. ➙ Work with small amounts of material.• Insert more intensely colored opaque dentin cervically.• Incisally cover thin areas with warmer tones (special porcelain).• Create a transition to cutting edge/mamelons for soft, meshed transition.• Possibly repeat the ring to solidify the material.Cutting edge• Complete the tooth shape incisally with incisal porce-lain.• Layer the shape approximately one-fourth larger to compensate for shrinkage during ring.• Raise the incisal pin by 1 mm on the articulator.Fig 5-78 Ceramic veneering. (a) Prepare the framework of a veneer crown. (b) Carry out oxide ring. (c) Apply/re the opaquer. (d) Apply/re the dentin material. (e) Layer/re the cutting edge. abcde 179Fabricating a Three-Unit Partial Denture and Inner TelescopeFig 5-78 (cont) (f) Perform corrective reduction of the veneer into the appropriate shape. (g) Check the tooth shape. (h) Prepare the surface. (i) Apply glaze/staining. (j) Fire the glaze with ceramic stains. Corrective reduction• Prepare contact points and check them.• Machine out shape characteristics and overprepare.• Establish the height and width of the tooth.• Ensure that the tip of the canine is displaced mesially.• Position the vestibular medial ridge in a fanglike fashion.• Create marginal ridges that are convex mesially.• Ensure that the distal marginal ridge has a pronounced embrasure.Tooth shape• Are the length and width of the tooth correct?• Does the vestibular surface have a convex shape?• Are the angle and mass characteristics present?• Have the margin and medial ridges been created properly?• Does the size t with the other teeth?• Are topographic details (eg, dental tubercle) present?Occlusal reduction• Overprepare the tooth surface with sharp diamonds and roughen slightly.• Create developmental grooves on the vestibular surface.• Do not introduce any roughness interdentally because of the risk of plaque accumulation.Glaze/staining• Check the tooth color by applying staining uid.• Apply glaze if there are very pronounced rough areas, and ll up depressions with glaze.• Carry out only very discreet staining of the tooth.• Do a breakdown of the shades used.Glaze ring• Surface structure glazes on ring.• Use the manufacturer’s information.• Tooth surface must display a closed, glassy structure.• Shape and surface characteristics must remain notice-able.fghij 180Telescopic Anchoring and Supporting ElementsFig 5-79 Finishing the milled work and polishing. (a) Clean the framework. (b) Rework milled surfaces and interlock. (c) Finish the occlusal surfaces. (d) Buff and polish the surfaces. (e) Clean and perform a nal check.Cleaning• Carefully airborne-particle abrade the framework using a pen-type abrasion tool.• Under no circumstances abrade the ceramic; cover it with wax or a nger.• Reduce abrasion pressure to 2 bars.• Abrade the inside of the crown until clean (and watch for oxide and ceramic residues).• Clean the attachment/occlusal surfaces with polishing beads (which makes nishing and polishing easier).Reworking• Remill the milled surfaces with a milling tool.• Use a suitable, correct-size tungsten carbide cutter combined with milling oil.• Work at the specied revolutions per minute so that no chatter marks or scratches are created.Finishing• Perform corrective reduction of occlusal details with a blunt spherical bur.• Smooth any aws in the wax processing.• Occlusal relief may have some rough areas.• The structure and shape of the occlusal surface is discernible.• It must be possible to identify the kind of tooth.Bufng/polishing• Smooth metal surfaces with stones and rubber polishers.• First use abrasive rubber polishers, then use ne rubber polishers for a very smooth surface.• Perform polishing and high-glaze nishing, possibly using a handpiece with suitable polishing pastes (eg, nonprecious metal with diamond polishing paste).Final clean/check• Steam-clean the partial denture.• Handle the ceramic veneer very carefully (risk of cracks above 145°C).• All polishing debris and oxide residues must be removed.• All of the surfaces must be smooth and have no rough areas (especially interdentally).abcde

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