Features of Partial Dentures










Features of
Partial Dentures
81
De nition and Indications
When the periodontal tissue is used to support replacement teeth via rigid connection
to the residual dentition, this approach belongs to the area of partial prosthodontics.
Partial edentulousness is treated with a prosthetic structure in which the arti cial teeth
are  rmly connected to some of the residual teeth, and the masticatory forces acting on
the tooth replacement are absorbed entirely by the periodontium of the residual teeth in-
volved. These structures are known as partial dentures. Figure 3-1 provides an overview
of the various components of partial dentures.
When a partial denture is  tted, the edentulous jaw segments are not loaded by mas-
ticatory pressure. Rigidly connecting several or all residual teeth by means of a partial
denture produces a functional unit in which all the stresses of the unit act equally on all
the involved teeth.
The tooth that is prepared to receive a partial denture is known as an abutment tooth.
A crown that is  xed onto an abutment is called an anchor; it is the retaining part of the
partial denture. The term pontic refers to the individual tooth replaced by the partial
denture body; a partial denture between the canine and  rst molar therefore contains
two anchors and one body that consists of two pontics. The functional unit of this partial
denture structure consists of the periodontal tissues of the abutment teeth (canine and
rst molar), the abutment teeth themselves, and the pontic teeth (premolars) as the par-
tial denture body (Figs 3-2 to 3-4). Owing to the rigid construction, the replaced teeth are
supported entirely by the periodontium.

82
Features of Partial Dentures
Partial denture classication
Retaining part Connecting part
Partial denture anchor on abutment
Partial denture body with individual pontics
Removable Fixed Placement in the dental arch Partial denture body design
Partly
removable
Form of
anchor
Terminal partial denture
Cantilever
partial
denture
Space partial denture Contact partial denture
Partial
anchor
Full anchor
Fully
removable
Partial
anchor
Single unit Multi-unit Sanitary
partial
denture
Slit partial
denture
Tangential
partial
denture
Saddle
partial
denture
Pontic has extensive
contact; unfavorable
in hygiene terms
Pontic has point contact;
very favorable in
hygiene terms
Pontic at slitlike distance
(approximately 1 mm)
from the mucosa
Pontic at a large distance
from the mucosa
(approximately 3 mm)
Pontic anchored at one end only,
with no terminal abutment
Several pontics between different
partial denture abutments
Interdental insertion partial
denture with pontics between
abutments
Full-coverage crowns, partial
crowns, post crowns, inlays,
and thimble crowns
Screwed telescopic
attachments
Bolted telescopic
attachments
Fig 3-1 Partial denture components.

83
Denition and Indications
Partial dentures are indicated if missing teeth
have to be replaced to restore the statics and
function within a closed dental arch. Masticatory
function is restored (therapeutic function), and
the adjacent teeth and antagonists are prevented
from migrating into the space. This is the only
way to avoid malocclusions and temporomandib-
ular joint (TMJ) changes and to reduce shrinkage
of the edentulous parts of the arch. Remedying
an unsightly change to the face caused by visible
loss of teeth is an important indication for a par-
tial denture (regulative function).
The periodontium of abutment teeth needs to
meet certain requirements; if the tooth replace-
ment is supported entirely on the periodontium,
the abutment teeth have to bear additional stress-
es apart from the masticatory pressure directed
onto them. Ideally, abutment teeth should be vi-
tal. Teeth that have undergone endodontic treat-
ment may only be used as abutments if they have
healthy and noninamed periodontium (Fig 3-5).
The root shape of the abutment teeth is also
important: Cylindric, round roots are less suit-
able than attened ones. Multirooted teeth with
splayed roots offer greater security than fused,
convergent roots (Fig 3-6). Curved irregular roots
are also more suitable than completely conical
roots.
The abutment teeth should be rmly anchored
in the jaw and should not have a short or wide
Fig 3-2 An edentulous space can be closed with a xed partial
denture. The teeth bordering the space are rst prepared by
corrective reduction. Together with their periodontal tissues,
they form the abutments.
Fig 3-3 The partial denture forms a functional unit between
the periodontal tissues of the prepared teeth, the crowns, and
the pontics, which form the partial denture body.
Anchor
Body
Abutment teeth
Fig 3-4 The parts of a partial denture are the anchors (retainer),
the abutment teeth, and the body, which consists of the pon-
tics and the connector between the abutments and the pontics.

84
Features of Partial Dentures
periodontium. Two abutment teeth can usually
bear two pontics. Another relationship explains
this better: The root surface area (periodontal sur-
face area) of the abutment teeth must be as big as
or bigger than the root surface area of the teeth
being replaced (Figs 3-7 and 3-8).
A partial denture is contraindicated if two abut-
ment teeth have to bear more than two pontics; in
this situation, an implant to help ll the gap may
become necessary. A xed partial denture is also
contraindicated if several adjacent teeth need to
be replaced but there is no terminal abutment.
A removable partial denture can be used for this
purpose. A xed partial denture is also not ap-
propriate if the pontics cannot be easily shaped
because of severe shrinkage of the alveolar pro-
cesses (ie, if parts of the alveolar ridge have to be
replaced by the xed partial denture and thus be-
come uncleanable). A removable partial denture
may be considered in these circumstances.
The assessment of whether abutment teeth
will withstand the loading caused by the pontics
should take into consideration that the periodon-
tal tissues of abutment teeth have limited adapt-
ability to increased stress. In this connection, an
increase in Sharpey bers may be observed in the
Fig 3-5 A partial denture is a periodontally supported tooth
replacement, which is why the periodontal tissues of the abut-
ment teeth have to meet certain requirements. Vital teeth are
the ideal abutments, but above all, the periodontium must be
healthy and not inamed. The usability of a tooth can be deter-
mined by the ratio of root length to crown length: Ideally the
root should be twice as long as the crown.
OS
RS
Fig 3-6 The shape of the root is another measure of a tooths
usability as an abutment. Flattened, splayed roots in multi-
rooted teeth are better suited than round roots that are close
together.
Fig 3-7 A good measure of the usability of a tooth as an abut-
ment is the ratio of the area of its occlusal surface (OS) to the
area of its root surface (RS); the root surface area should be
ve times that of the occlusal surface.

85
Function of Partial Dentures
periodontal space. An abutment tooth is there-
fore secured by the partial denture if the partial
denture is constructed accurately.
Function of Partial
Dentures
Restoration of a complete dental arch with a xed
partial denture restores full masticatory function
and thereby contributes to the patient’s well-
being. Sagittal support within the dental arch can
be restored by a partial denture when an existing
edentulous space is closed. In an interrupted den-
tal arch, horizontal force components cannot be
transferred via approximal contact points, which
means potential overloading of individual teeth.
A partial denture therefore takes on the support-
ing function for the entire dental arch.
The rigid partial denture structure is intended
to have a therapeutic action. In a periodontally
damaged residual dentition, the therapeutic ac-
tion involves rigidly connecting the remaining
teeth to each other and limiting pathologic tooth
mobility. This rigid connection between residual
teeth is known as splinting. Above all, horizontal
force components acting on the alveolar peri-
odontal tissue are reduced in this way. In terms of
splinting, a distinction is made between primary
splinting, which is done by splinting the residual
teeth with xed constructions such as partial den-
tures and bar connectors, and secondary splint-
ing, which involves a rigidly anchored removable
structure (Fig 3-9).
Primary splinting is achieved with xed partial
dentures using several abutments and pontics, so
that the splinting can encompass the entire den-
tal arch. Secondary splinting can be done with
removable partial dentures or partial dentures
in which the splinting is achieved via telescopic
anchors or precision attachments (Fig 3-10). The
splinting effect is the same for both forms, but
secondary splinting has the advantage of bet-
ter oral hygiene maintenance. Partial splinting
means rigidly connecting single teeth or groups
of teeth; full splinting involves rigidly connecting
all the teeth, for example, by a 14-part partial den-
ture or a rigidly anchored partial prosthesis.
The edentulous parts of the jaw are protected
against mechanical masticatory inuences by a
partial denture. This applies mainly to the mar-
ginal periodontium in tooth spaces. Resorption of
edentulous jaw segments is alleviated by contact
partial dentures and is stable over prolonged pe-
riods.
The closed occlusal eld of a partial denture
not only provides sagittal support for the dental
arch in which it is located but also delivers the
necessary occlusal support for the opposing den-
tal arch. When there is a gap between the teeth,
Fig 3-8 The choice of an abutment tooth depends primarily on how many pontics it has to bear. As a rule of thumb, one abutment
tooth can receive one pontic. To put it another way, the root surface area of the abutment teeth should be as large or larger than
the root surface area of the teeth being replaced. (a) The common situation in which the two premolars are being replaced and are
borne by the canine and the rst molar is very good because the root surface area of the abutments is more than twice that of the
teeth being replaced. (b) If the missing teeth are to be borne by a canine and a second molar, the solution is inadequate.
a b

86
Features of Partial Dentures
the adjacent teeth incline into the space; a partial
denture will prevent this. The antagonists would
also supererupt into the gap if they do not have an
opposing occlusal force. In extreme cases, these
teeth erupt until they come into contact with the
opposing jaw. The resulting malocclusions are so
severe that such a tooth usually has to be pulled
into position during prosthodontic work.
Supereruption (lengthening) of individual an-
tagonists can be prevented by promptly fabricat-
ing a partial denture, which will thus provide sup-
port to the opposing dental arch. An overerupted
tooth means severe loosening for a dental arch
because the approximal contacts are lost. It is al-
most as if there were a gap in the opposing dental
arch too.
A gap within a dental arch means that chew-
ing efciency is greatly impaired. The patient
will usually chew on the undamaged side, which
causes overloading on that side, not only for the
teeth and their supporting structures but also for
the TMJ, and one-sided loading of the muscles
of mastication. Uniform and balanced loading of
the masticatory system is therefore prevented. As
functional adaptation of the tissue ensues, defor-
mation of the TMJ and changes to the neuromus-
cular system will occur. The space must be closed
with a partial denture so that the patient feels no
impediment when speaking. Spaces between an-
terior teeth greatly interfere with speech, espe-
cially the pronunciation of consonants (c, d, s, t,
and z). A partial denture needs to accurately close
this kind of space, including space in the inter-
dental area, because small interdental spaces due
to an articial interdental papilla cause the patient
to spit unintentionally when speaking. A partial
denture must therefore take into account speech
function achieved with the closed dental arch.
Characteristics of Partial
Dentures
Different types of partial dentures are required
for different topographic situations in a partially
edentulous dentition. For instance, the following
types of partial dentures are identied according
to their placement in the dental arch (Fig 3-11):
Unilateral interdental insertion partial denture
(posterior on one side)
Fig 3-9 An excellent splinting effect is achieved
with a partial denture. As a result of the rigid
connection, all the teeth absorb the masticatory
pressure that arises. Periodontally damaged
dentition can be therapeutically treated by
splinting structures. Primary splinting occurs if a
xed partial denture is cemented in place; sec-
ondary splinting is achieved by a removable
partial denture.
Fig 3-10 There is a difference between xed and removable partial dentures.
(a) In removable partial dentures, abutments have a double-crown structure, for
example, telescopic crowns or tapered crowns; the subcrowns are xed, and
the actual prosthesis with outer crowns is removable. (b) A xed partial denture
consists of a block and is rmly inserted.
a
b

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Features of Partial Dentures81De nition and IndicationsWhen the periodontal tissue is used to support replacement teeth via rigid connection to the residual dentition, this approach belongs to the area of partial prosthodontics. Partial edentulousness is treated with a prosthetic structure in which the arti cial teeth are  rmly connected to some of the residual teeth, and the masticatory forces acting on the tooth replacement are absorbed entirely by the periodontium of the residual teeth in-volved. These structures are known as partial dentures. Figure 3-1 provides an overview of the various components of partial dentures. When a partial denture is  tted, the edentulous jaw segments are not loaded by mas-ticatory pressure. Rigidly connecting several or all residual teeth by means of a partial denture produces a functional unit in which all the stresses of the unit act equally on all the involved teeth.The tooth that is prepared to receive a partial denture is known as an abutment tooth. A crown that is  xed onto an abutment is called an anchor; it is the retaining part of the partial denture. The term pontic refers to the individual tooth replaced by the partial denture body; a partial denture between the canine and  rst molar therefore contains two anchors and one body that consists of two pontics. The functional unit of this partial denture structure consists of the periodontal tissues of the abutment teeth (canine and  rst molar), the abutment teeth themselves, and the pontic teeth (premolars) as the par-tial denture body (Figs 3-2 to 3-4). Owing to the rigid construction, the replaced teeth are supported entirely by the periodontium. 82Features of Partial DenturesPartial denture classicationRetaining part Connecting partPartial denture anchor on abutmentPartial denture body with individual ponticsRemovable Fixed Placement in the dental arch Partial denture body designPartly removableForm of anchorTerminal partial dentureCantilever partial dentureSpace partial denture Contact partial denturePartial anchorFull anchorFully removablePartial anchorSingle unit Multi-unit Sanitary partial dentureSlit partial dentureTangential partial dentureSaddle partial denturePontic has extensive contact; unfavorable in hygiene termsPontic has point contact; very favorable in hygiene termsPontic at slitlike distance (approximately 1 mm) from the mucosaPontic at a large distance from the mucosa (approximately 3 mm)Pontic anchored at one end only, with no terminal abutmentSeveral pontics between different partial denture abutmentsInterdental insertion partial denture with pontics between abutmentsFull-coverage crowns, partial crowns, post crowns, inlays, and thimble crownsScrewed telescopic attachmentsBolted telescopic attachmentsFig 3-1 Partial denture components. 83Denition and IndicationsPartial dentures are indicated if missing teeth have to be replaced to restore the statics and function within a closed dental arch. Masticatory function is restored (therapeutic function), and the adjacent teeth and antagonists are prevented from migrating into the space. This is the only way to avoid malocclusions and temporomandib-ular joint (TMJ) changes and to reduce shrinkage of the edentulous parts of the arch. Remedying an unsightly change to the face caused by visible loss of teeth is an important indication for a par-tial denture (regulative function).The periodontium of abutment teeth needs to meet certain requirements; if the tooth replace-ment is supported entirely on the periodontium, the abutment teeth have to bear additional stress-es apart from the masticatory pressure directed onto them. Ideally, abutment teeth should be vi-tal. Teeth that have undergone endodontic treat-ment may only be used as abutments if they have healthy and noninamed periodontium (Fig 3-5).The root shape of the abutment teeth is also important: Cylindric, round roots are less suit-able than attened ones. Multirooted teeth with splayed roots offer greater security than fused, convergent roots (Fig 3-6). Curved irregular roots are also more suitable than completely conical roots.The abutment teeth should be rmly anchored in the jaw and should not have a short or wide Fig 3-2 An edentulous space can be closed with a xed partial denture. The teeth bordering the space are rst prepared by corrective reduction. Together with their periodontal tissues, they form the abutments.Fig 3-3 The partial denture forms a functional unit between the periodontal tissues of the prepared teeth, the crowns, and the pontics, which form the partial denture body.AnchorBodyAbutment teethFig 3-4 The parts of a partial denture are the anchors (retainer), the abutment teeth, and the body, which consists of the pon-tics and the connector between the abutments and the pontics. 84Features of Partial Denturesperiodontium. Two abutment teeth can usually bear two pontics. Another relationship explains this better: The root surface area (periodontal sur-face area) of the abutment teeth must be as big as or bigger than the root surface area of the teeth being replaced (Figs 3-7 and 3-8).A partial denture is contraindicated if two abut-ment teeth have to bear more than two pontics; in this situation, an implant to help ll the gap may become necessary. A xed partial denture is also contraindicated if several adjacent teeth need to be replaced but there is no terminal abutment. A removable partial denture can be used for this purpose. A xed partial denture is also not ap-propriate if the pontics cannot be easily shaped because of severe shrinkage of the alveolar pro-cesses (ie, if parts of the alveolar ridge have to be replaced by the xed partial denture and thus be-come uncleanable). A removable partial denture may be considered in these circumstances.The assessment of whether abutment teeth will withstand the loading caused by the pontics should take into consideration that the periodon-tal tissues of abutment teeth have limited adapt-ability to increased stress. In this connection, an increase in Sharpey bers may be observed in the Fig 3-5 A partial denture is a periodontally supported tooth replacement, which is why the periodontal tissues of the abut-ment teeth have to meet certain requirements. Vital teeth are the ideal abutments, but above all, the periodontium must be healthy and not inamed. The usability of a tooth can be deter-mined by the ratio of root length to crown length: Ideally the root should be twice as long as the crown.OSRSFig 3-6 The shape of the root is another measure of a tooth’s usability as an abutment. Flattened, splayed roots in multi-rooted teeth are better suited than round roots that are close together.Fig 3-7 A good measure of the usability of a tooth as an abut-ment is the ratio of the area of its occlusal surface (OS) to the area of its root surface (RS); the root surface area should be ve times that of the occlusal surface. 85Function of Partial Denturesperiodontal space. An abutment tooth is there-fore secured by the partial denture if the partial denture is constructed accurately.Function of Partial DenturesRestoration of a complete dental arch with a xed partial denture restores full masticatory function and thereby contributes to the patient’s well-being. Sagittal support within the dental arch can be restored by a partial denture when an existing edentulous space is closed. In an interrupted den-tal arch, horizontal force components cannot be transferred via approximal contact points, which means potential overloading of individual teeth. A partial denture therefore takes on the support-ing function for the entire dental arch. The rigid partial denture structure is intended to have a therapeutic action. In a periodontally damaged residual dentition, the therapeutic ac-tion involves rigidly connecting the remaining teeth to each other and limiting pathologic tooth mobility. This rigid connection between residual teeth is known as splinting. Above all, horizontal force components acting on the alveolar peri-odontal tissue are reduced in this way. In terms of splinting, a distinction is made between primary splinting, which is done by splinting the residual teeth with xed constructions such as partial den-tures and bar connectors, and secondary splint-ing, which involves a rigidly anchored removable structure (Fig 3-9).Primary splinting is achieved with xed partial dentures using several abutments and pontics, so that the splinting can encompass the entire den-tal arch. Secondary splinting can be done with removable partial dentures or partial dentures in which the splinting is achieved via telescopic anchors or precision attachments (Fig 3-10). The splinting effect is the same for both forms, but secondary splinting has the advantage of bet-ter oral hygiene maintenance. Partial splinting means rigidly connecting single teeth or groups of teeth; full splinting involves rigidly connecting all the teeth, for example, by a 14-part partial den-ture or a rigidly anchored partial prosthesis.The edentulous parts of the jaw are protected against mechanical masticatory inuences by a partial denture. This applies mainly to the mar-ginal periodontium in tooth spaces. Resorption of edentulous jaw segments is alleviated by contact partial dentures and is stable over prolonged pe-riods.The closed occlusal eld of a partial denture not only provides sagittal support for the dental arch in which it is located but also delivers the necessary occlusal support for the opposing den-tal arch. When there is a gap between the teeth, Fig 3-8 The choice of an abutment tooth depends primarily on how many pontics it has to bear. As a rule of thumb, one abutment tooth can receive one pontic. To put it another way, the root surface area of the abutment teeth should be as large or larger than the root surface area of the teeth being replaced. (a) The common situation in which the two premolars are being replaced and are borne by the canine and the rst molar is very good because the root surface area of the abutments is more than twice that of the teeth being replaced. (b) If the missing teeth are to be borne by a canine and a second molar, the solution is inadequate.a b 86Features of Partial Denturesthe adjacent teeth incline into the space; a partial denture will prevent this. The antagonists would also supererupt into the gap if they do not have an opposing occlusal force. In extreme cases, these teeth erupt until they come into contact with the opposing jaw. The resulting malocclusions are so severe that such a tooth usually has to be pulled into position during prosthodontic work. Supereruption (lengthening) of individual an-tagonists can be prevented by promptly fabricat-ing a partial denture, which will thus provide sup-port to the opposing dental arch. An overerupted tooth means severe loosening for a dental arch because the approximal contacts are lost. It is al-most as if there were a gap in the opposing dental arch too.A gap within a dental arch means that chew-ing efciency is greatly impaired. The patient will usually chew on the undamaged side, which causes overloading on that side, not only for the teeth and their supporting structures but also for the TMJ, and one-sided loading of the muscles of mastication. Uniform and balanced loading of the masticatory system is therefore prevented. As functional adaptation of the tissue ensues, defor-mation of the TMJ and changes to the neuromus-cular system will occur. The space must be closed with a partial denture so that the patient feels no impediment when speaking. Spaces between an-terior teeth greatly interfere with speech, espe-cially the pronunciation of consonants (c, d, s, t, and z). A partial denture needs to accurately close this kind of space, including space in the inter-dental area, because small interdental spaces due to an articial interdental papilla cause the patient to spit unintentionally when speaking. A partial denture must therefore take into account speech function achieved with the closed dental arch.Characteristics of Partial DenturesDifferent types of partial dentures are required for different topographic situations in a partially edentulous dentition. For instance, the following types of partial dentures are identied according to their placement in the dental arch (Fig 3-11):• Unilateral interdental insertion partial denture (posterior on one side)Fig 3-9 An excellent splinting effect is achieved with a partial denture. As a result of the rigid connection, all the teeth absorb the masticatory pressure that arises. Periodontally damaged dentition can be therapeutically treated by splinting structures. Primary splinting occurs if a xed partial denture is cemented in place; sec-ondary splinting is achieved by a removable partial denture.Fig 3-10 There is a difference between xed and removable partial dentures. (a) In removable partial dentures, abutments have a double-crown structure, for example, telescopic crowns or tapered crowns; the subcrowns are xed, and the actual prosthesis with outer crowns is removable. (b) A xed partial denture consists of a block and is rmly inserted.ab 87Characteristics of Partial Dentures• Bilateral interdental insertion partial denture (posterior on both sides)• Frontal interdental insertion partial denture (an-terior)• Laterofrontal interdental insertion partial den-ture with abutment blocks (joined anterior and posterior)• Laterofrontolateral interdental insertion partial denture (continuous single partial denture com-prising a posterior area extending over the ante-rior teeth to the posterior teeth)• Laterofrontal interdental insertion partial den-ture (three single partial dentures over an entire dental arch)• Laterofrontal interdental insertion partial den-ture combined with a removable free-end saddle • Continuous partial denture over the entire den-tal archIn addition, xed and removable partial den-tures have different characteristics. Fixed partial dentures are cemented onto the abutment teeth and therefore cannot be removed for cleaning. They offer patients a feeling of security as they provide an intact dental arch, and patients do not have to constantly confront their mutilated denti-tion when they take out the appliance. Hygiene conditions with xed partial dentures are often poor, which not only leads to unpleasant breath odor but also means damage to the residual den-tition or mucosa underneath the restoration.Fully removable partial dentures are better for periodontal hygiene and often have a denture saddle that serves as an alveolar ridge replace-ment. One advantage of a removable partial den-ture is that the entire structure does not become unusable if an abutment tooth is lost. In the case of a xed restoration, the loss of an abutment tooth usually means loss of the entire appliance. Furthermore, the marginal periodontal tissues are more readily accessible for further dental treatment in the case of removable partial den-tures. Partly removable dentures (or detachable dentures) are screw retained on primary crowns and can only be taken out by a dentist.Interdental insertion partial dentures are used in a tooth space where the teeth bordering the gap serve as the abutment teeth. They are also called terminal partial dentures because the pon-tics are bordered by abutments. If the partial den-ture is mounted between the abutments without interruption, this is known as a single-span termi-nal partial denture. If several pontics are mounted between different abutments in several regions, this structure may be called a multispan terminal xed partial denture (Fig 3-12). Multispan terminal Unilateral Bilateral ContinuousFrontal Laterofrontal LaterofrontolateralFig 3-11 Classication of partial dentures based on placement in the dental arch. 88Features of Partial Denturespartial dentures close several edentulous gaps, which is why the term alternating interdental in-sertion partial denture with one or more central abutments can also be used.Cantilever xed partial dentures are structures in which one pontic is anchored to an abutment on one side and the replacement tooth is cantile-vered to close an edentulous gap; cantilever xed partial dentures can also be used to complete shortened dental arches. A terminal partial denture may be xed onto normal interdental insertion partial dentures and combine both forms of partial dentures. Anchor-ing a cantilever pontic to an abutment tooth is not advised because this cantilever pontic always represents a lever arm, leading to nonphysiologic tipping and rotation of the abutment tooth. The longer the lever arm, the greater the nonphysi-ologic loading, which leads to loosening and loss of the abutment tooth.Installation of a cantilever xed partial denture is possible if the terminal pontic is suspended on two splinted crowns or an interdental insertion partial denture. In both cases, however, the canti-lever pontic should not be wider than a premolar. For longer-span free-end gaps, a terminal implant is necessary as a terminal abutment.Characteristics of Partial Denture AbutmentsFull crowns made of metal, veneer crowns, post crowns, thimble crowns, and jacket crowns can be used as partial denture abutments. Three-surface inlays can only be used to anchor pros-theses in exceptional cases (Fig 3-13).A metal full crown is ideal for anchoring the partial denture. It offers the greatest mechanical strength and highest anchoring force because, compared with other types of crowns, it has the most compact structure. Full crowns entirely en-compass the abutment teeth without the loss of a great deal of dental tissue from corrective re-duction. A full crown offers the greatest stability, even in the case of weakened and damaged den-tal crowns.The protective function of a full crown against caries and the precise shaping of the crown mar-gin offer advantages in terms of partial denture anchorage. Outside the visible area, full-cast crowns are preferable to any other type of crown as abutments; in the visible sections of the dental arch, veneer crowns are preferred for anchoring the appliance. Acrylic resin and ceramic veneers are the available options.The advantage of an acrylic resin veneer is that, if dislodged, veneers can be repaired in the mouth if necessary; the partial denture does not have to be removed and become unusable for a time. Modern composites are sufciently abra-sion resistant and hence unproblematic in the oc-clusal or incisal area. Acrylic resins swell and age, which leads to increased deposition of contami-nants, discoloration of the material, and signs of mucosal inammation.Ceramic veneers are abrasion resistant and have the best color effect under all lighting condi-tions. Ceramic veneers are also suitable for full veneers when the occlusal circumstances are Fig 3-12 If a prosthesis unit is mounted between the abutments without interruption, this is known as a single-span partial den-ture; if several pontics are mounted between several abutments, the structure is known as a multispan terminal partial denture in reference to the terminal abutments between which the pontics are mounted. A multispan partial denture therefore closes several edentulous gaps, which is why the term alternating interdental insertion partial denture with one or more central abutments is more accurate. It is possible to retain a prosthesis unit on an abutment on one side so that the replacement tooth is cantilevered. This is called a cantilever xed partial denture.Single-span terminal partial denture Multispan terminal partial denture Cantilever xed partial denture 89Characteristics of Partial Denture Abutmentsstraightforward. Compared with full-metal crowns, veneer crowns have the following disadvantages as partial denture abutments: The crown frame-work is unstable, the tooth has to be reduced more extensively, and the fabrication of veneer crowns is more prone to error.Thimble crowns are especially suitable for par-tial dentures (Fig 3-14). Thimble-like metal crowns are cemented onto teeth that have undergone extensive preparation; the metal crown encases the preparation like a full crown and thereby sta-bilizes it. Externally, the thimble crown has a ta-pered shape. Between these crowns, the pontics are soldered in place or cast in a single piece. The pontics may have the same tapered shape as the thimble crowns. The size of the approximal con-nector is reduced to the minimum dimensions necessary.Jacket crowns are used as the veneer for thim-ble crowns. The relatively compact thimble partial denture framework bears the individual crowns. The advantage of this is that defective crowns can easily be replaced. The disadvantage of thimble constructions in general is the considerable loss of tooth substance because of the extensive cor-rective reduction required.AFig 3-13 All types of coronal restorations are suitable as abutments. (A) A full-cast crown is the most stable but has the disadvantage of being esthetically unsatisfactory. (B) In exceptional cases, multisurface inlays may also be used as a form of anchorage. (C) In the visible area, a veneer crown structure is appropriate. (D) Pivot teeth have only limited use as abutments because the abutment tooth is devitalized. (E) Partial crowns are safe abutments, provided adequate retentions for the crowns are available. Fig 3-14 Thimble crowns are a special form of abut-ment with a cervical shoulder; they are cemented onto the prepared teeth. In addition, these crowns are joined together by narrow bars. For the pontics, bars are also tted between the thimble crowns. The prepared teeth are protected by a thin layer of metal and can be covered with any crown design. If the pon-tics and crowns are fabricated and tted individually, the individual components can easily be replaced. Relatively soft acrylic resin crowns can be placed, and these can be replaced after a short wearing period if they become discolored or are severely abraded.BCDE 90Features of Partial DenturesPartial crowns are used as abutments in the vi-sual area of the dental arches for esthetic reasons, though extensive inlays can also be integrated. Poor stability, risk of caries development, and the time-consuming and error-prone method of fabri-cation are drawbacks of such abutments. Precise channel-shoulder-pin retention is required for partial crowns as abutments.Because post crowns can only be tted to devi-talized teeth, they have very limited use as abut-ments. Only the maxillary canines may be consid-ered as terminal abutments; the maxillary central incisors and mandibular canines are possible as central abutments. The holes on post crowns rarely coincide with the path of insertion of the other abutments, which is why in such cases a core crown should be prepared (ie, a separate root post with core buildups that is coordinated with the insertion path of the other abutments and cemented in place separately).Acrylic resin crowns can be used as abutments for large acrylic resin partial dentures for a maxi-mum of three-unit anterior interdental insertion partial dentures. All-ceramic crowns (eg, IPS Em-press, Ivoclar; In-Ceram, Vita) are also suitable as abutments for small edentulous gaps in the ante-rior region.Resin-bonded partial dentures are indicated for anterior single-tooth edentulous gaps. For this purpose, a veneered metal framework with two lingual wings is bonded onto the abutments bor-dering the gap using the acid-etch technique. For better guidance, the lingual wings can easily be extended into the enamel without the dentin be-ing exposed.Bonded Partial DenturesMinimally invasive restorations, which can be produced without substance-abrading prepara-tion or surgery on the bone, can be achieved with metal or all-ceramic bonded partial dentures. Ac-cording to the current state of the art, a single-wing all-ceramic bonded partial denture with a framework of zirconia-ceramic is the classic form of restoration for single-tooth spaces in the an-terior region. Metal-ceramic bonded partial den-tures became known internationally as Maryland bridges as early as 1970; more commonly known today as resin-bonded prostheses, these are elec-trolytically etched, double-wing, metal-ceramic bonded partial dentures (Figs 3-15 and 3-16).Bonded partial dentures are used to treat single- tooth gaps between posterior teeth in the maxilla and mandible as well as the maxillary anterior re-gion. They are placed on neighboring teeth that border the gap and are free of caries or llings. Bonded partial dentures are also indicated in the case of congenitally missing maxillary lateral incisors, the gap having been widened and the required sagittal space created beforehand by orthodontic treatment so that removal of dental hard tissue is minimal.Bonded partial dentures for posterior teeth are preferably made from a ceramic-veneered metal framework; for anterior teeth, they are all-ceramic. Nonprecious-metal re-on alloys based on cobalt-chrome and nickel-chrome have a high modulus of elasticity and can be cemented more success-fully than precious-metal alloys. High-strength framework ceramics, such as glass-infiltrated aluminum oxide ceramic or zirconia-ceramic, are esthetically better for anterior partial dentures.The success rates of metal-ceramic bonded par-tial dentures are roughly equivalent to those of conventional partial dentures; even single-wing bonded partial dentures have proved successful. The advantages of bonded partial dentures in-clude the following:• They are minimally invasive; that is, only a small amount of natural tooth substance is removed.• They do not cause pulp irritation.• The costs are relatively low.• Anesthesia is not required.• They do not rule out alternative restorative op-tions.Single-wing bonded partial dentures have ad-ditional advantages: (1) No nonphysiologic splint-ing is required. (2) Preparation is simpler because abutment teeth do not have to be parallelized.The disadvantages of cemented joints are the following:• Extensive treatment is required because of the difcult enamel-bordered tooth preparation.• Cementation is time-consuming.• The cemented bond is prone to failure. 91Bonded Partial DenturesThe space required for the framework and cemented joint—about 0.8 mm—has to be pre-pared; a retentive preparation design greatly in-creases the stability of the cemented bond. The retainer wings should have a minimum material thickness of 0.7 mm for adequate rigidity in the case of metal frameworks or sufcient strength in the case of ceramic components.Preparation of the abutment teeth involves creating usable bonding surfaces with mechani-cal retentions by making narrow grooves in the enamel, which also serve as retentive reinforce-ment against bending and peeling of the metallic retainer wings. The rigid ceramic retainer wings require no retentive preparation on abutment teeth, only shallow depressions for clear posi-tioning of the partial denture. Narrow approximal retention channels are prepared with slightly ta-pered separating diamonds in the enamel only; an intraoral parallelometer makes it easier to pre-pare parallel channels. In addition, creation of a shallow approximal box (approximately 0.5 mm deep and 2 × 2 mm wide) toward the pontic can strengthen the framework at critical points (Fig 3-17).If a bonded partial denture debonds, it may be swallowed or inhaled. Therefore, a checkup every 6 to 12 months is absolutely essential. Further-Conditioned inner surfacesWraparoundEtched surfacesrcaFig 3-15 Bonded prostheses can be designed with lingual wraparounds as retainer wings. The prepared surfaces on the teeth are edged with end grooves and pre-etched; the inner surfaces of the wraparounds are conditioned so that a silane layer can be applied. The cemented joint between the components and the abutments is achieved with composite.Fig 3-16 The retention surfaces or retainer wings must lie so that there are no parafunctional occlusal contacts that would tear apart the cemented joint on loading. In the case of double-wing bonded prostheses, one wing might become detached without being noticed, creating a gap under which caries lesions will form. Preparation of the retention surface must therefore create enough space to guarantee the minimum material thickness of the retainer wing and cement layer and provide space for adequate freeway.Fig 3-17 For metal frameworks, parallel, approximal retention grooves (r) need to be placed in the enamel, which requires use of an intraoral parallelometer. For all-ceramic frameworks, it is enough to mill an ap-proximal box (a) 0.5 mm deep. A chamfer (c) for a central nub makes it easier to position the retainer wings. 92Features of Partial Denturesmore, caries damage may occur under a detached retainer wing. Patients should be advised about the risk of swallowing or aspirating the appliance if it becomes detached.Adhesive retention in a mechanochemical bond by means of corundum blasting, application of a silane coupling agent, and cementation with spe-cial monomer cements requires acid etching of the dental enamel. Opaque cements are used for metal-ceramic bonded partial dentures, whereas all-ceramic partial dentures are xed with tooth-colored cements. The retentive surface of the tooth is etched with 37% orthophosphoric acid, thoroughly sprayed with water, and air dried. After application of a composite cement to the retention surfaces of the bonded partial denture and the tooth, the appliance is held in position until the cement sets.Bonded attachments can be used to retain par-tial prostheses as an alternative to cast clasps, double crowns, or attachments integrated into crowns. With bonded attachments, the cement joint acts as a predetermined breaking point upon overloading; tooth fractures do not occur because usually only the retainer wings become detached. The retainer wings of bonded attachments made of cobalt-chromium alloys should be at least 0.7 mm thick to provide adequate rigidity. They bear extracoronal slide attachments with a replaceable resin matrix. Approximally to the prosthesis sad-dle, retainer wings have a recessed rest area or a parallel contact plate for the secondary structure; an additional oral encircling catch can be milled to secure the attachment position.Partial Denture Body DesignFixed partial dentures must be designed to create favorable hygiene conditions and a natural ap-pearance. Fixed partial dentures are categorized based on the nature of the spatial relationship to the edentulous dental arch: Contact appliances have mucosal contact, and space partial dentures do not. Contact xed partial dentures can also be differentiated by the amount of mucosal contact (Fig 3-18).In tangential partial dentures, the unit is lin-gually drawn inward toward the mucosa until the body touches the round alveolar ridge tangential-ly. The contact is without pressure and punctate. To ensure that the partial denture can be rinsed through, the interdental areas between the pon-tics and abutments are left clear. However, this only applies to the posterior region. In the an-terior dentition, this kind of clearance cannot be created because the natural appearance—and certainly phonetics—might suffer. A broader rest area is required in the anterior region.The tangential contact of the partial denture is shifted vestibularly. This means that the vestibu-lar tooth shape can be extended to its natural length. The partial denture body must be brought steeply toward the alveolar ridge so there are no niches where contaminants could accumulate. The contact with the mucosa must not be made of acrylic resin or else a dense coating of shed, dead mucosal cells will form on the resin, which has a tendency to swell, leading to severe inam-mation of the mucosa. A narrow metal strip at the cervical margin of the partial denture pontics cannot be avoided because the retention for the acrylic resin requires a box-shaped design.With ceramic-veneered pontics, tangential mu-cosal contact can be achieved with the ceramic red to a high glaze. However, the contact must still be punctate and pressure free. It is also im-portant to ensure that the partial denture body can be thoroughly rinsed, avoiding the interden-tal papilla in the posterior region and the lingual surface of the partial denture sloping steeply to-ward the tangential contact.A saddle is a type of partial denture body that has extensive contact with the mucosa, almost overlying it like a base. In special cases, a root ex-tension can be sunk into the socket of the extract-ed teeth. This design should be rejected, however, because appliances seated over a broad area are impossible to clean. Furthermore, they prevent mucosal cells from being shed underneath the saddle. This and the hygiene problems lead to chronic inammation and even tumorlike tissue changes.In the anterior region, a broader rest area is required for esthetic and phonetic reasons. How-ever, a saddle structure should also be rejected here. The rest area is designed to be linear and to 93Partial Denture Body Designhave a maximum width of 3 mm. If this still does not satisfy the esthetic demands, a removable partial denture construction with a broad rest area may be the solution. If an extensive rest area cannot be avoided with an anterior xed partial denture, the better salivary ow, more favorable cleanability, and suction effect during chewing will make it less likely that inammation will de-1. Hygienic partial denture2. Slit partial denture4. Saddle partial denture5. Pontic partial denture3. Tangential partial dentureFig 3-18 In terms of body design, there is a difference between hygienic and contact prostheses. This refers to the relationship between the pontic and the alveolar ridge. Five possibilities can be identied: (1) A hygienic (or sanitary) partial denture is classied as a supramucous partial denture; that is, it has no contact with the mucosa. (2) A slit partial denture has no direct contact with the mucosa but is about 1 mm from the mucosa. (3) A tangential partial denture as a contramucous partial denture has only point contact with the alveolar ridge; as a result, niches can develop where contaminants may accumulate. (4) A saddle partial denture has extensive mucosal contact, which is extremely unfavorable in terms of hygiene for a long-term restoration. (5) Pontic partial dentures or intramucous partial dentures have a root extension that has extremely broad contact with the jaw. Fixed partial dentures should not have broad, extensive mucosal contact. If a broad rest area is necessary for esthetic reasons, the partial denture should be removable. 94Features of Partial Denturesvelop. Hence, the rejection of a saddle should be weighed against these issues.As a result of the pressure-free, point contact of the partial denture body, masticatory loading initi-ates a stimulus on the mucosa and jaw bone via axial tooth mobility. This halts the progressive shrinkage of edentulous sections of the dental arch.Space partial dentures have no contact with the jaw mucosa. For esthetic reasons, such designs can only be used in the posterior region and only then in the mandible. Such devices are available in two types: slit and sanitary or hygienic types.A hygienic pontic has a heart-shaped cross sec-tion with a minimum height of 3 mm. This cross section offers adequate rigidity against bending and enhances cleanability. The appliance can be thoroughly rinsed with a minimum gap of 3 mm to the alveolar ridge. If the gap is smaller, there is a risk that food particles will become lodged. The span width of hygienic pontics should not exceed a molar’s width to guarantee adequate exural ri-gidity and ensure that the alveolar process is not reduced by the massaging effect of tongue and cheek.The gap between the mucosa and a slit partial denture is about 1 mm. Slit partial dentures are more difcult to clean but are necessary if the minimum thickness of the sanitary pontic could not otherwise be achieved or if the esthetic im-pression would suffer.Connection Between the Partial Denture Body and the AnchorHigh-quality casting techniques involved in metal processing make it possible to cast any partial denture design in a single piece. This provides a homogenous, rigid connection between abut-ments and the partial denture body. It is reason-able to assume that impression materials and methods give equally accurate models, making it unnecessary to do a framework try-in with di-vided partial denture structures. An undivided, rigid partial denture framework with at least two abutments can only be inserted in a dened path, so the teeth must be prepared so that they are parallel to each other. If the abut-ment teeth are severely tipped, making the pre-pared teeth parallel is only possible with substan-tial loss of dental tissue. Loss of tooth substance also puts the pulp at risk.If corrective reduction cannot be performed in parallel for the abutment teeth, especially in multi-span partial dentures, the partial denture can be divided into individual components or into a complete assembly of partial components that are assembled in the mouth to form a rigid con-nection (Figs 3-19 and 3-20). If the plan is to ex-tend the partial denture, the division is made at an abutment where this extension is expected to take place. A large variety of prefabricated con-nector components are available for this prospec-tive planning so that the appliance can later be extended into combined prostheses.Division by means of an attachment to a weak-ened abutment tooth can relieve that abutment if the attachment allows slight movement corre-sponding to axial tooth mobility. The dentist de-cides where and when the division of a partial denture structure is necessary, because dividing the appliance is not straightforward. For instance, the splinting effect may be lost, or slight mobile connections may exert a lever effect on the abut-ment teeth.Hand-fabricated or prefabricated attachments are available as divided slide attachments. It is important to ensure that the path of insertion for the attachment coincides with that of the abut-ment to which the pontic is rmly connected.Precision attachments have a limited range of use as dividing members because they do not have a rigid connection and permit movement within the path of insertion. This also applies to the possibility of covering an abutment tooth with a telescopic double crown. In this case, the path of insertion of the outer crown must match that of the other abutment teeth.A rigid connection can only be created if the di-vided partial denture parts are screwed together (Fig 3-21). In this case, an extension to an abut-ment will engage in the pontic. A drill hole is placed through the pontic and extension, which bears the thread in the extension part. The two parts are then joined and rmly screwed together intraorally. A precisely rigid connection is pro-duced if the extension engages in the pontic like an attachment. 95Connection Between the Partial Denture Body and the AnchorFig 3-19 If the axes of the abutment teeth greatly converge, a rigid, undivided framework cannot be inserted. In this case, the framework can be divided and joined together intraorally. The framework is joined using a dividing attach-ment that is placed parallel along the path of insertion of an abutment; the abutments are cemented onto the abutment teeth so that the divided partial denture forms a closed block in the mouth.Fig 3-20 Where abutments are diver-gent, post crowns in the form of core crowns can be fabricated based on the direction of inclination of the abut-ments. A rigid structure can easily be inserted. The loading capacity of a pivot tooth is limited compared with that of a healthy abutment tooth. If the direction of loading in relation to the periodon-tium of the pivot tooth is altered by the coronal axis, the loading may be too great for the pivot tooth.Fig 3-21 Division may become neces-sary if the individual abutments are sig-nicantly inclined toward each other. In this case, a screw connection provides the necessary rigid join between pontic and anchor.It is advantageous to place the screw guidance lingually to buccally; a screw connection directed occlusally should be covered with veneer mate-rial to prevent contamination. The threaded por-tion and screw are prefabricated components that can be cast on and allow the connection to be detached at any time; hence, the divided partial denture can be replaced or expanded. The tech-nical working method of fabricating abutments and bodies separately, veneering (with ceramic), and soldering the parts in the nal working step does not constitute a divided partial denture but equates to a one-piece cast partial denture.For a multispan partial denture, it may be ad-vantageous to fabricate the prosthesis in sepa-rate parts, re on ceramic, then solder the parts together (Fig 3-22). This avoids stresses in the framework that occur as a result of waxing up during casting and especially during ring. This technical trick is strongly recommended for multi-span partial dentures.Fig 3-22 For ceramic-veneered multispan prostheses, it is ad-visable to fabricate the partial denture in several parts and join them together intraorally. This division can be achieved with a dividing attachment that permits relative movement of the par-tial denture parts. Stresses arising from masticatory forces and those caused by processing inaccuracies are offset by division of a multispan partial denture. 96Features of Partial DenturesAcrylic resin–veneered partial dentures are sol-dered together after a framework try-in. A preci-sion impression is taken of the framework parts in their correct relationship to each other; the frame-work parts can be xed and soldered together on the correction model. A further advantage is that stresses are compensated for. The veneer is obvi-ously not applied until after the soldering stage.Removable Partial DenturesThe major drawback to xed partial dentures lies in the adverse hygiene conditions they create. This can be compensated for by the construction of a removable partial denture, which is a peri-odontally supported tooth replacement, except that the anchors are divided so that the actual partial denture framework can be reduced (Figs 3-23 and 3-24).Removable partial dentures are being used in-creasingly and, based on their construction, could be classied as partial prostheses. How ever, they do not have a prosthesis framework and differ very little from xed partial dentures in their basic construction. This is why they fall into the same category.Unlike the described abutments for xed partial dentures, the anchors for removable partial den-tures have several components:• Primary anchors are rmly cemented onto the prepared tooth. These may be subcrowns for a telescopic or tapered (conical) crown or full crowns with an attachment matrix.• Secondary anchors are rmly attached to the prosthesis. These may be outer crowns for tele-scopic or tapered crowns or the secondary at-tachment components.• Tertiary anchors are additional anchorage com-ponents that rigidly connect to the aforemen-tioned partial anchors. These can be latches, bolts, screws, or springs.There is a technical t between the primary and secondary anchors. The design of tertiary anchors for a removable restoration is dependent on whether the prosthesis is partly or fully remov-able.Partly removable (eg, screw-retained) restora-tions can only be removed by a dentist. These de-signs resemble a divided prosthesis but have the advantage that parts can be replaced or the ap-pliance can be extended outside the mouth. Be-cause partly removable restorations can only be removed at long time intervals, the bodies should be designed as for a xed restoration. Partly re-movable restorations therefore have only tangen-tial contact with the mucosa of the jaw in the area of the pontics, which gives them the quality of a divided xed restoration.Fully removable partial dentures can be taken out by patients themselves because they are con-nected using latch designs. Fully removable par-tial dentures are the real alternative to a xed re-placement. The hygiene conditions are extremely favorable, and the appliances can be extended, which allows for repairs and relining outside the mouth.Jaw segments can be replaced with fully re-movable partial dentures if there is severe shrink-age of the alveolar ridge. Rests can be created on the jawbone, as in xed partial dentures. For example, removable partial dentures can also be combined with mucosa-borne cantilever parts. Another advantage is that the individual abut-ments do not have to share a common path of in-sertion. This is produced by the primary anchors for the framework.One disadvantage of removable partial den-tures is that more extensive preparation of the abutment teeth is required for double crowns than for full anchors on xed restorations. If ve-neered abutments are also required, the critical limit for preparation is usually exceeded. All of the reported drawbacks of parallel ts also apply to this kind of restoration. The technical effort in-volved in complex designs is not in reasonable proportion to the outcome. An equally good res-toration could probably be achieved with a less time-consuming partial prosthesis. 97Removable Partial DenturesFig 3-23 Removable partial dentures have the advantage of allowing more favorable hygiene conditions than xed partial dentures. Removable partial dentures are entirely periodon-tally borne restorations, even if parts of the alveolar ridge are replaced by the removable partial denture. Removable partial dentures can only be placed in edentulous gaps; wide-span cantilever parts can be secured with terminal implant posts. An-chorage to the residual dentition and onto implants is achieved with attachments, telescopic parts with latching mechanisms, or tapered designs.Fig 3-24 If a large-span free-end gap is to be restored with a removable partial denture, the free-end gap can be tted with one or more implants on which the prosthesis is supported. The mixed support from periodontal and bony tissue may negatively affect the implant, however, so attempts have been made to relieve the implant with resilient mesostructures (in-tramobile elements). 98Features of Partial DenturesPartial Denture StaticsThe design of periodontally supported restora-tions must not place excessive strain on the load-ing capacity of the abutments. Otherwise, con-stantly changing forces from different directions will destroy the tissues supporting the teeth. A partial denture must therefore be worked so that all horizontally acting (ie, not axial) stresses on the abutments are largely avoided; excessive ax-ial stresses on the abutment teeth must be ruled out. The loading of a restoration is inuenced by the following:• The length and dimensions of the body• The position (inclination) of the abutment teeth• The shaping of the occlusal surfaces• The path of the bodyThe length and dimensions of the restoration body depend on its span length. Long units are not as rigid as short ones because they might bend. The degree of bending (deection) of a body with a xed cross section increases to the power of three as a function of its length. To put it another way, if a 1-m-long bar bends by a xed amount under loading, a bar of twice that length X 2X 3XFig 3-25 The deection of a partial denture can cause extreme loading of abutments and therefore must be discussed as a func-tion of its cross section and length. (a) A thick, short beam will hardly bend at all because of the small weight load. (b) A beam that is twice as long but has the same cross section will bend eight times as much. (c) For the same cross section but three times the length, the beam deects exactly 27 times as much. T1/2TFig 3-26 The deection depends on the thickness of the ma-terial. A beam of a specied length and thickness (T) bends only slightly as a result of the weight placed upon it. If the beam has the same length but only half the original thickness (½T), this beam will deect exactly eight times as much.a b c 99Partial Denture Staticswill bend under the same load not twice as much but exactly eight times as much; for three times the span length (3 m), deection is 27 times as high (Fig 3-25). The cross-section dimensions (height and width) have a similar inuence on the deection of the restoration body. The amount of deection increases eightfold if the span length is the same but the cross section of the body is halved; a thin board will bend more than a thick one (Fig 3-26).The deection of a body that rests on two sup-ports is dependent on the shape of its cross sec-tion; that is, a board bends much more if it is laid at but hardly yields at all if placed on its edge. Applying that principle to the restoration body, the cross section of a unit can be reduced to the shape of a T-beam, which has very high bending stiffness (exural rigidity). Given the high-quality materials used, a pontic with a thickness of at least 3 mm has sufcient exural rigidity.For multispan bodies, however, a cross section dimension of approximately 5 mm2 should be set to ensure adequate rigidity. Appliances with poor dimensions will bend, and the abutment teeth will tip toward the body and sustain axial loading (Fig 3-27).The foundations of a structural prosthesis may be assumed to stand rm, whereas the founda-tions (abutment teeth) of a dental prosthesis move under load. To simplify the comparison, a pontic can be seen as suspended between two pillars (abutments). If a force acts in the middle of the structure, both abutments are equally loaded; that is, they are pressed into the sockets until the periodontium stops the movement and produces a counterforce (Fig 3-28). If the force does not act in the middle but is shifted toward one abut-ment, the loading is greater on that abutment and smaller on the more distant abutment. By exten-sion, this means that if the force acts exactly over one abutment, this will absorb the full force while the other abutment apparently remains unload-ed. However, appearances can be deceptive.Torque (torque = force applied × lever arm) works by means of the forces acting on each structure. The force applied acts with a lever arm (length of the prosthesis span) around the more distant abutment. A counterforce in the periodon-tium of the rst abutment produces an opposing torque with the span length of the prosthesis. However, the torques are not equal in size be-cause the force applied presses on the abutment SHSVFig 3-27 If a partial denture span is too long, deection can cause two problems: tipping of the abutments and formation of a gap at the surfaces of terminal abutments facing away from the prosthesis. A gap of varying size will develop, depend-ing on the shape of the preparation margin. A small horizontal gap will form (SH) in the case of a chamfer preparation; given the same deection of the partial denture body, shoulder prep-aration will result in a vertical gap (SV).Fig 3-28 If a partial denture is loaded exactly in the middle, the resulting load on the abutments will also be exactly in the middle. Each abutment will bear the same load, which may mean overloading for an anterior tooth serving as the anchor for a posterior partial denture. 100Features of Partial Denturesso that it sinks into the socket, and the prosthesis is rotated by exactly this amount of sinking and tips the distant abutment into its socket (Figs 3-29 and 3-30).Tipping is dependent on the length of the whole structure. The amount of rotation can never be greater than the amount to which the abutments can be pressed into their sockets. If one abutment sinks into the socket as far as the limit of its load-ing capacity, the other abutment can only be tipped up to the limit of its loading. This applies only to forces acting in parallel to the abutment axes. Only very minimal rotation is produced in a long prosthesis, while a short partial denture, in which the loaded abutment is pressed into its socket, will tip the distant abutment more markedly.ABABCFig 3-29 If the load on the same partial denture is unilaterally shifted to one end of the partial denture body, the load distribu-tion for the individual abutments will also be shifted. One abut-ment tooth (B) has to bear the main masticatory pressure, and the partial denture rotates around the other abutment tooth (A) with a torque comprised of masticatory force and prosthesis length. The amount of rotation depends on how far the abut-ment tooth (B) can be sunk into its socket.Fig 3-30 A system involving three abutments can be compared with a beam supported on three springs, which rotates around the opposite abutment when loaded on one side. It is wrong to assume that the beam would rotate around abutment B. It could only do that if abutment B were jointed but rigidly supported. A multispan partial denture has relatively stable support because rotations around an abutment cannot exceed the amount to which the other abutments can be pressed into their periodontal tissues. In a multispan partial denture, the loading relations for abutment C do not change if masticatory force acts exactly on that abutment. In addition, the basic loading does not change for the terminal abutment (A) at the other end. However, it is weakened by force being absorbed by abutment B. 101Path of the Partial Denture BodyPath of the Partial Denture BodyThe path, length, and shape of the occlusal sur-faces inuence loading of the abutment teeth. It is advisable to keep the body straight to reduce the effects of tipping forces. Generally speaking, two abutments should bear only two pontics so that axial overloading is avoided.If two abutments linked by a restoration unit also bear a cantilever pontic, a torque acts on the structure with a lever arm that is equivalent to the length of the cantilever pontic. The torque acts around the abutment that is nearest to the canti-lever pontic. Torque also arises in the opposite di-rection around that abutment with the lever arm, equating to the length of the unit between the abutments. The force for this has to be produced by the periodontal tissue of the distant abutment because this abutment is put under tensile stress.In terms of the geometric relationships, the longer the pontic, the less opposing force is nec-essary because torque follows the rst principle of levers: force exerted on the cantilever pontic × cantilever length. However, this makes it clear that, for a cantilever partial denture with only one abutment (crown with cantilever extension), the total torque acts on the abutment. Therefore, such designs should be avoided (Figs 3-31 to 3-35).Because the teeth are always arranged in the form of an arch, a long-span restoration must follow the path of that arch; this becomes clear with a terminal abutment prosthesis in the ante-rior region: The abutments would be the canines, and the pontics would be the incisors, following the path of the dental arch. If a force then acts in parallel to the abutment axes precisely in the middle of the prosthesis body, torque is produced around the abutments. The lever arm is the dis-tance between a straight line connecting the ca-nines and the height of the dental arch. In reality, this distance can be greater than 10 mm. In this case, the arched body acts like a cantilever partial denture.Two basic principles therefore emerge: (1) The body of the partial denture must run straight be-tween the abutments. (2) If possible, additional abutment teeth should be used (increasing abut-ments). The additional anchorage must be at the same distance from the torque axis as the (possi-ble) force being exerted. In a model case, the rst two premolars would be sufcient as additional anchors.During mandibular movements, the antagonis-tic occlusal surfaces move against each other hor-izontally. As a result, horizontal loading can arise FF2Fig 3-31 Loading of a partial denture and its abutments is ad-versely affected by a cantilever pontic. Because of a force (F) on the cantilever pontic, the prosthesis is loaded with a torque that must be counteracted by a torque with force F2. The possi-ble rotation takes place via the abutment next to the cantilever pontic. Deection of the middle pontic is not ruled out.Fig 3-32 If several teeth are splinted and a cantilever pontic is attached to them, torques will load the structures via this pontic. Rotation happens at the middle abutment, while the abutment at the cantilever pontic is subjected to pressure and the opposite abutment to tensile stress. The loading is non-physiologic for all the teeth involved. 102Features of Partial DenturesFig 3-33 Several cantilever pontics can be secured with an implant that supports the gap. This structure behaves like a ter-minal abutment in which the whole masticatory load is trans-ferred to the abutment teeth—and here to an implant as well.Fig 3-34 The case in which an abutment tooth is covered by a cantilever pontic is particularly unfavorable. A crown with canti-lever extension subjects the abutment tooth to so much tipping that this design rarely lasts long. If the cantilever pontic is also a tooth with occlusal surfaces and the abutment is an anterior tooth, the life span of this restoration is likely to be very limited. The case in which a canine is occupied by a cantilever pontic (a small incisor, in fact) is relatively common. In this case, the canine is preferentially subjected to rotation around the vertical axis. This results in tooth migration and means that often the canine can no longer be used for further prosthodontics.Fig 3-35 When examining the torques in the case of cantilever pontics, it is clear that the arched arrangement of the teeth can become a problem when restoring with long-span partial dentures. In an anterior partial denture from canine to canine, the anterior teeth run labially in a wide arch. The possible rotation axis moves linearly from canine to canine. When the anterior teeth are loaded, a torque acts in the distance from the canine connecting line as far as the point of force application in the horizontal. Hence, there is a requirement for a prosthesis to run straight between the abutments. In the case of a maxillary anterior partial denture, lateral abutments must be used for support. The further the lateral partial denture abutment is from the rotation axis, the better it can counteract the torque. 103Path of the Partial Denture Bodyfor the partial denture and hence for the abut-ments. The size of the load depends on whether the cusps are worked in keeping with TMJ guid-ance or only adapted to centric occlusion. Steep, tall cusps produce greater horizontal loading than at ones; the cuspal inclination of the adjacent teeth is a useful support. Horizontal loads are lim-ited if antagonist contact occurs in exact intercus-pation with multipoint contact where the occlusal patterns have been adapted to the patient’s indi-vidual movement pattern (Fig 3-36).A decrease in horizontal and axial loading is achieved if the pontic is roughly two-thirds the normal width of the tooth being replaced (Fig 3-37). Once again, higher and more effective sur-face pressure can be produced for the same mas-ticatory force if the occlusal surface is narrow. Furthermore, in the posterior region, a pontic is easier to shape for tangential mucosal contact if the occlusal surface is reduced by the specied amount.The position and inclination of the abutments also inuence abutment loading. Whether an abutment tooth is loaded horizontally or axially depends on what inclination the tooth has in re-lation to the force striking it. Extremely inclined (displaced) teeth are less suitable as abutments than straight, upright teeth. If a tooth space has remained unrestored for a long time, the teeth bordering the gap—the potential abutment teeth—may already have inclined markedly into the space.The disadvantage is clear: Much tooth sub-stance has to be removed to make the teeth roughly parallel. On normal loading, however, the abutment teeth will never absorb the pres-sure truly axially (centrally) to their periodontium but always eccentrically. In exceptional cases, it will be necessary to upright the teeth again by suitable orthodontic measures.XX2/3XFig 3-36 Loading of the pontics is unfavorable if the occlusal surfaces are incorrectly shaped. If the cusps are too high, the pontic will be subject to tipping during lateral excursions of the mandible. The requirements that the prosthesis unit must be straight and the width of the replacement tooth must be smaller make it difcult to shape the occlusal contact correct-ly, which is why special, careful checks are needed.Fig 3-37 In the posterior region, the replacement teeth (pon-tics) are modeled to be two-thirds the width of a normal tooth. This does not mean that masticatory pressure on the pontics is reduced but that periodontal hygiene is considerably better. 2/3X

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