Removable Partial Dentures










Removable Partial
Dentures
105
Classi cation of Partially Edentulous Arches
As the dentition deteriorates from a fully dentate masticatory system to a fully eden-
tulous jaw, various edentulous situations arise that demand different solutions when
planning prosthodontic treatment. Note, however, that there is a difference between
edentulous spaces and shortened dental arches. Edentulous space denotes the situation
where one or more teeth are missing within a dental arch and the gap is bounded by
natural teeth. A shortened dental arch or free-end gap refers to the situation where tooth
loss occurs at the end of the dental arch. Following is a simple description of the types of
partially edentulous dental arches (Wild’s classi cation) without specifying the number
of missing teeth (Fig 4-1):
• Interrupted dental arch
• Shortened dental arch
• Interrupted and simultaneously shortened dental arch

106
Removable Partial Dentures
Dental arch interrupted
and shortened
Dental arch interrupted unilaterally,
bilaterally, or several times
Dental arch shortened unilaterally
or bilaterally
Fig 4-1 Wild’s classication of partially edentulous arches differentiates between edentulous space and a shortened dental arch as
well as a combination of edentulous situations.
Types of partially edentulous arches can also
be grouped into comparable dentition situations.
Two fundamental classications are based on the
topography of the residual dentition and the bio-
static conditions.
The Kennedy topographic (or morphologic)
classication describes the dentition of the in-
dividual jaws, so it can be used equally for the
maxilla and the mandible. Four basic classes are
identied (Fig 4-2):
1. Bilaterally shortened dental arch
2. Unilaterally shortened dental arch
3. Posterior edentulous space
4. Anterior edentulous space
This classication is further divided into vari-
ous subcategories:
Residual dentition is interrupted by one other
space
Residual dentition is interrupted by several spaces
• Only minimal residual dentition remains
This morphologic classication can be used
to assess the statics of a denture during design
planning for the individual jaws and to select the
abutments for a rigid construction or for the rest
seats that will support the denture.
Assessment of the functional state in a partially
edentulous arch is not possible with such a clas-
sication, making it difcult to plan the optimal
denture design. When assessing the damage to
the dentition, it is important to know how many
teeth are missing and where they are missing. For
example, the function of the masticatory system
is not disrupted if all four third molars are miss-
ing, yet functional impairment occurs if the maxil-
lary incisors have all been lost. In addition to the
poor esthetic impression, speech and biting func-
tion are impeded. Or if four posterior teeth are
missing on one side of the jaw, masticatory func-
tion is greatly impaired.
The criterion used in the Eichner classication
to describe the functional level of the residual
dentition is to name the antagonistic groups of
teeth in the jaw (Fig 4-3). The classication is
based on the biostatic condition of the dentition
and describes antagonist contact in four support
areas (Fig 4-4):
1. Premolars on the left side
2. Premolars on the right side
3. Molars on the left side
4. Molars on the right side
The support function of such an area is depen-
dent on whether a clearly dened occlusal con-
tact exists in the area (Figs 4-5 to 4-7). For this to
be the case, it is not necessary for all the teeth to
be present. Complete contact exists, for instance,
if the mandible still bears the two second premo-

107
Classication of Partially Edentulous Arches
lars and the second molars and the correspond-
ing main and secondary antagonists are still
present in the maxilla. Canines and incisors are
disregarded in terms of the support areas.
Depending on an edentulous situation resulting
in the loss of one or more support areas, different
stresses will affect the temporomandibular joints,
the muscles of mastication, and the periodontal
tissue of the remaining teeth. The Eichner classi-
cation of the partially edentulous arch categorizes
antagonist contact in the four support areas into
three classes, each with three subgroups (Fig 4-8).
During denture planning, the Eichner classica-
tion can provide information about antagonistic
loading conditions, while topographic classica-
tion identies the abutments for a partial denture.
1. Bilaterally shortened
dental arch
2. Unilaterally
shortened dental arch
3. Posterior edentulous
space
4. Anterior edentulous
space
Residual
dentition
interrupted by
one other gap
Residual
dentition
interrupted by
several gaps
Minimal
residual
dentition
Fig 4-2 The Kennedy topographic classication describes the distribution of spaces, which is categorized into four classes and
three subgroups.

108
Removable Partial Dentures
I
III
II
IV
Fig 4-7 Biostatic balance is totally disrupted if only the an-
terior teeth remain. This partially edentulous dentition has no
support area contact and reects the same biostatic condition
as complete tooth loss.
Fig 4-3 The functional level of a partially edentulous dental
arch can be described by recording the antagonistic pairs of
teeth. This gure shows a schematic representation of two an-
tagonistic dental arches. Complete supporting function in the
dentition only exists if there is antagonist contact throughout.
Fig 4-4 Classication of the dental arches into four support
areas: (I) premolars on the left side, (II) premolars on the right
side, (III) molars on the left side, and (IV) molars on the right
side.
Fig 4-5 The biostatic status of the dentition is inadequate if
antagonist contact is not present in all of the support areas.
When there are four missing teeth, two support areas are with-
out contact.
Fig 4-6 Biostatic balance may still exist in a greatly reduced
residual dentition if, as shown here for a case of 10 residual
teeth, antagonist contact is present in all four support areas.

109
Classication of Partially Edentulous Arches
Group A1 Group A2 Group A3
Group B1 Group B2 Group B3 Group B4
Group C1 Group C2 Group C3
Fig 4-8 The Eichner classication categorizes support area contacts into three groups: Groups A1 through A3 show antagonist
contact in all four support areas, groups B1 through B4 show antagonist contact but not in all support areas, and groups C1 through
C3 show no antagonist contact.

110
Removable Partial Dentures
Classication of Partial
Dentures
Partial dentures can be classied according to the
nature of tissue loading or the topography of the
partially edentulous arch (Fig 4-9).
Classication according to tissue
loading
Classication according to tissue loading takes
into account the functional level of the denture.
The basic categories are periodontally supported,
mucosa-borne, or bone-supported tooth restora-
tions.
A periodontally supported prosthesis is a physi-
ologic design because masticatory pressure is
transferred solely to the periodontium of the re-
maining teeth via symmetrically arranged abut-
ments. The denture contacts the edentulous al-
veolar ridge but does not put any load on it. The
design is similar to a partial denture construc-
tion. Where the abutments are asymmetrically
arranged, the restoration is supported on the re-
sidual dentition, but the denture also rests on the
mucosa.
A mucosa-borne prosthesis without support on
the residual dentition transfers masticatory pres-
sure to the mucosa. In relation to partial dentures,
such structures can be used as interim solutions.
Because there is considerable loading of the mar-
gin with this kind of prosthesis, the area resting
on the mucosa should be very large, though the
marginal periodontium should be avoided. A full
denture is a mucosa-borne restoration that has
an extended prosthesis base.
Prostheses with mixed support are used for
shortened dental arches in the form of cantilever
xed partial prostheses. The dentures rest on the
alveolar ridge and are supported periodontally at
one end only. These structures are statically inde-
terminate systems because the mucosal support
can only absorb masticatory forces to a limited
extent and can hardly absorb transverse forces
at all, while the periodontal support takes on all
masticatory forces depending on the quality of
the retentive component. The periodontal sup-
port is usually overloaded and loosened because
of the unstable mucosal support.
Support on implants is another method of seat-
ing partial dentures. The denture body is xed
symmetrically onto implants that are inserted into
the jawbone and bear the prosthesis. The denture
is then a bone-supported restoration.
Mixed support, in which the denture is supported
simultaneously on the residual dentition, mucosa,
and implants, is statically indeterminate because
of the variable resilience of the rest areas involved.
The result is variable loading of the involved rest
areas.
Classication according to
edentulous topography
Classication according to edentulous topogra-
phy provides a precise description of the form
of the denture based on the distribution of gaps
across the dental arches. Interdental insertion
pros theses replace teeth within a dental arch. They
are essentially supported on the remaining teeth,
which means that insertion dentures belong to the
group of periodontally borne or supported resto-
rations. Following are types of insertion dentures:
Unilateral interdental insertion prostheses on
one half of the jaw are supported on both halves
of the jaw; the supporting components are
joined by a denture framework.
Bilateral interdental insertion prostheses on
both halves of the jaw are joined by means of
a denture framework. Large arch-shaped inter-
dental segments are possible for patients with
a small anterior residual dentition but terminal
molars.
Anterior interdental insertion prostheses replace
missing anterior teeth. If a long, arched path ex-
tends to the premolars, this denture acts as a
cantilever xed partial prosthesis.
Alternating interdental insertion prostheses re-
place single teeth in several small edentulous
spaces over the entire dental arch.

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Removable Partial Dentures105Classi cation of Partially Edentulous ArchesAs the dentition deteriorates from a fully dentate masticatory system to a fully eden-tulous jaw, various edentulous situations arise that demand different solutions when planning prosthodontic treatment. Note, however, that there is a difference between edentulous spaces and shortened dental arches. Edentulous space denotes the situation where one or more teeth are missing within a dental arch and the gap is bounded by natural teeth. A shortened dental arch or free-end gap refers to the situation where tooth loss occurs at the end of the dental arch. Following is a simple description of the types of partially edentulous dental arches (Wild’s classi cation) without specifying the number of missing teeth (Fig 4-1):• Interrupted dental arch• Shortened dental arch• Interrupted and simultaneously shortened dental arch 106Removable Partial DenturesDental arch interrupted and shortenedDental arch interrupted unilaterally, bilaterally, or several timesDental arch shortened unilaterally or bilaterallyFig 4-1 Wild’s classication of partially edentulous arches differentiates between edentulous space and a shortened dental arch as well as a combination of edentulous situations.Types of partially edentulous arches can also be grouped into comparable dentition situations. Two fundamental classications are based on the topography of the residual dentition and the bio-static conditions.The Kennedy topographic (or morphologic) classication describes the dentition of the in-dividual jaws, so it can be used equally for the maxilla and the mandible. Four basic classes are identied (Fig 4-2):1. Bilaterally shortened dental arch2. Unilaterally shortened dental arch3. Posterior edentulous space4. Anterior edentulous spaceThis classication is further divided into vari-ous subcategories:• Residual dentition is interrupted by one other space• Residual dentition is interrupted by several spaces• Only minimal residual dentition remainsThis morphologic classication can be used to assess the statics of a denture during design planning for the individual jaws and to select the abutments for a rigid construction or for the rest seats that will support the denture.Assessment of the functional state in a partially edentulous arch is not possible with such a clas-sication, making it difcult to plan the optimal denture design. When assessing the damage to the dentition, it is important to know how many teeth are missing and where they are missing. For example, the function of the masticatory system is not disrupted if all four third molars are miss-ing, yet functional impairment occurs if the maxil-lary incisors have all been lost. In addition to the poor esthetic impression, speech and biting func-tion are impeded. Or if four posterior teeth are missing on one side of the jaw, masticatory func-tion is greatly impaired.The criterion used in the Eichner classication to describe the functional level of the residual dentition is to name the antagonistic groups of teeth in the jaw (Fig 4-3). The classication is based on the biostatic condition of the dentition and describes antagonist contact in four support areas (Fig 4-4):1. Premolars on the left side2. Premolars on the right side3. Molars on the left side4. Molars on the right sideThe support function of such an area is depen-dent on whether a clearly dened occlusal con-tact exists in the area (Figs 4-5 to 4-7). For this to be the case, it is not necessary for all the teeth to be present. Complete contact exists, for instance, if the mandible still bears the two second premo- 107Classication of Partially Edentulous Archeslars and the second molars and the correspond-ing main and secondary antagonists are still present in the maxilla. Canines and incisors are disregarded in terms of the support areas.Depending on an edentulous situation resulting in the loss of one or more support areas, different stresses will affect the temporomandibular joints, the muscles of mastication, and the periodontal tissue of the remaining teeth. The Eichner classi-cation of the partially edentulous arch categorizes antagonist contact in the four support areas into three classes, each with three subgroups (Fig 4-8). During denture planning, the Eichner classica-tion can provide information about antagonistic loading conditions, while topographic classica-tion identies the abutments for a partial denture.1. Bilaterally shortened dental arch2. Unilaterally shortened dental arch3. Posterior edentulous space4. Anterior edentulous spaceResidual dentition interrupted by one other gapResidual dentition interrupted by several gapsMinimal residual dentitionFig 4-2 The Kennedy topographic classication describes the distribution of spaces, which is categorized into four classes and three subgroups. 108Removable Partial DenturesIIIIIIIVFig 4-7 Biostatic balance is totally disrupted if only the an-terior teeth remain. This partially edentulous dentition has no support area contact and reects the same biostatic condition as complete tooth loss.Fig 4-3 The functional level of a partially edentulous dental arch can be described by recording the antagonistic pairs of teeth. This gure shows a schematic representation of two an-tagonistic dental arches. Complete supporting function in the dentition only exists if there is antagonist contact throughout.Fig 4-4 Classication of the dental arches into four support areas: (I) premolars on the left side, (II) premolars on the right side, (III) molars on the left side, and (IV) molars on the right side.Fig 4-5 The biostatic status of the dentition is inadequate if antagonist contact is not present in all of the support areas. When there are four missing teeth, two support areas are with-out contact.Fig 4-6 Biostatic balance may still exist in a greatly reduced residual dentition if, as shown here for a case of 10 residual teeth, antagonist contact is present in all four support areas. 109Classication of Partially Edentulous ArchesGroup A1 Group A2 Group A3Group B1 Group B2 Group B3 Group B4Group C1 Group C2 Group C3Fig 4-8 The Eichner classication categorizes support area contacts into three groups: Groups A1 through A3 show antagonist contact in all four support areas, groups B1 through B4 show antagonist contact but not in all support areas, and groups C1 through C3 show no antagonist contact. 110Removable Partial DenturesClassication of Partial DenturesPartial dentures can be classied according to the nature of tissue loading or the topography of the partially edentulous arch (Fig 4-9).Classication according to tissue loading Classication according to tissue loading takes into account the functional level of the denture. The basic categories are periodontally supported, mucosa-borne, or bone-supported tooth restora-tions.A periodontally supported prosthesis is a physi-ologic design because masticatory pressure is transferred solely to the periodontium of the re-maining teeth via symmetrically arranged abut-ments. The denture contacts the edentulous al-veolar ridge but does not put any load on it. The design is similar to a partial denture construc-tion. Where the abutments are asymmetrically arranged, the restoration is supported on the re-sidual dentition, but the denture also rests on the mucosa.A mucosa-borne prosthesis without support on the residual dentition transfers masticatory pres-sure to the mucosa. In relation to partial dentures, such structures can be used as interim solutions. Because there is considerable loading of the mar-gin with this kind of prosthesis, the area resting on the mucosa should be very large, though the marginal periodontium should be avoided. A full denture is a mucosa-borne restoration that has an extended prosthesis base.Prostheses with mixed support are used for shortened dental arches in the form of cantilever xed partial prostheses. The dentures rest on the alveolar ridge and are supported periodontally at one end only. These structures are statically inde-terminate systems because the mucosal support can only absorb masticatory forces to a limited extent and can hardly absorb transverse forces at all, while the periodontal support takes on all masticatory forces depending on the quality of the retentive component. The periodontal sup-port is usually overloaded and loosened because of the unstable mucosal support.Support on implants is another method of seat-ing partial dentures. The denture body is xed symmetrically onto implants that are inserted into the jawbone and bear the prosthesis. The denture is then a bone-supported restoration.Mixed support, in which the denture is supported simultaneously on the residual dentition, mucosa, and implants, is statically indeterminate because of the variable resilience of the rest areas involved. The result is variable loading of the involved rest areas.Classication according to edentulous topography Classication according to edentulous topogra-phy provides a precise description of the form of the denture based on the distribution of gaps across the dental arches. Interdental insertion pros theses replace teeth within a dental arch. They are essentially supported on the remaining teeth, which means that insertion dentures belong to the group of periodontally borne or supported resto-rations. Following are types of insertion dentures:• Unilateral interdental insertion prostheses on one half of the jaw are supported on both halves of the jaw; the supporting components are joined by a denture framework.• Bilateral interdental insertion prostheses on both halves of the jaw are joined by means of a denture framework. Large arch-shaped inter-dental segments are possible for patients with a small anterior residual dentition but terminal molars.• Anterior interdental insertion prostheses replace missing anterior teeth. If a long, arched path ex-tends to the premolars, this denture acts as a cantilever xed partial prosthesis.• Alternating interdental insertion prostheses re-place single teeth in several small edentulous spaces over the entire dental arch. 111Classication of Partial DenturesMucosa-borne dentures transfer the masticatory load to the mucosa aloneMinimal residual dentition requires almost complete denturesSuction, adhesive, and cohesive effects are of minor importance to partial denturesDentures with mixed support transfer the masticatory load to the mucosa and periodontiumPeriodontally supported dentures transfer the masticatory load to the periodontium aloneBone-supported dentures transfer the masticatory load directly to the boneCantilever xed partial dentures are used for unilateral, bilateral, or arched free-end gapsAnchorage with spring components such as clasps or spring anchorsInterdental insertion dentures are used for posterior, anterior, or alternating edentulous spacesAnchors via telescopic components are retained due to resistance to static frictionCombination of interdental insertion and cantilever xed partial dentures is used for appropriate gapsLatch systems for telescopic anchorageBased on the type of tissue loadingBased on the topography of the partially edentulous dentitionBased on the type of anchorage to the residual dentitionFig 4-9 Classication of partial dentures. 112Removable Partial DenturesFollowing are types of cantilever xed partial prostheses, a type that replaces teeth in short-ened dental arches:• Unilateral cantilever xed partial prostheses in a unilaterally shortened dental arch• Bilateral cantilever xed partial prostheses to re-place posterior teeth• Arched cantilever xed partial prostheses as almost-complete dentures in which a few termi-nal molars remain on one side onlyCombinations of cantilever xed partial and interdental insertion prostheses are used when there is a unilateral edentulous space with a unilateral shortened dental arch and an anterior edentulous gap. Each form of partially edentulous dentition requires a specic solution with a par-ticular form of denture and the necessary reten-tive components.Structural FeaturesIn principle, a removable partial denture is made of four structural sections, each of which has dif-ferent functional tasks (Fig 4-10):• Saddle• Framework or major connector• Anchoring elements• Supporting elementsThe denture saddle rests on edentulous jaw segments and bears the replacement teeth. To avoid pressure points, the denture saddle needs to t precisely to the alveolar ridge. High accu-racy of t also prevents movement of the saddle relative to the jaw. In this type of prosthesis, the denture saddle is adapted to its function; spe-cically, the three sections of the denture saddle have the following functions (Fig 4-11):• The denture base, which has direct mucosal contact, is designed to cover an extensive area as dened by the adjacent, mobile mucosal ar-eas. It must be possible to reline the area of the denture base.• The denture body forms the replacement for the resorbed alveolar ridge; it carries the articial teeth and provides buccal and lingual support. The basic principle is to reproduce the anatomi-cal form, especially in its spatial dimensions.• Replacement teeth are the substitute for the oc-clusal eld, masticatory function being restored by the articial teeth. Therefore, it is necessary to give the replacement teeth a functional ana-tomical form while enhancing the esthetic im-pression.The denture framework or the large connector represents the mechanical join between the den-ture saddles and the anchoring and supporting el-ements. These connectors can be fabricated from metal or acrylic resin. An acrylic resin plate is usu-ally constructed as a full plate or as a sectioned and partial plate; for stability reasons, the edge of the plate ts closely to the residual teeth. This results in encystment and inammation of the marginal periodontium, not to mention the me-chanical effects of the plate edges on this gingival region. Therefore, acrylic resin structures are only used for interim dentures; they are largely avoid-ed for partial dentures and have been replaced by model cast dentures. Metal constructions can be shaped as reduced plates, skeleton parts, or nar-row straplike connectors owing to the stability of the material.The anchoring elements secure the denture to the residual dentition and take on the function of retention. The supporting elements should sup-port the articial occlusal eld on the remaining teeth in order to transfer the masticatory forces periodontally. Anchoring and supporting ele-ments generally form a unit and create the link-age between the denture and the residual denti-tion. Depending on their design, they may take on a splinting function. The residual dentition is re-inforced via rigid anchoring elements or splinted by resilient connectors. As a result, uniform dis-tribution of forces to all the residual teeth can be achieved, and periodontally damaged teeth can be favorably supported by means of splinting.Mechanical ttings are used as anchoring and supporting elements on the residual dentition; they are differentiated as follows:• Fabrication of manually produced components (eg, clasps and telescopic crowns) and prefab-ricated (industrially produced) components (eg, attachments and anchors) 113Structural FeaturesDenture saddles in the area of the edentulous jaw segments bear the replacement teethThe denture framework is the major connector between the denture saddles and anchoring elementsThe anchoring and supporting ele-ments have retentive and supportive functionsFig 4-10 The structural features of a partial denture reect their assigned functions.Replacement toothDenture bodyDenture baseFig 4-11 The denture saddle comes in contact with the mucosa and bears the replacement teeth; it should t accurately against the jaw to avoid pressure points and prevent movement. The denture saddle has three functional parts: (1) Replacement teeth constitute the actual replace-ment of the occlusal eld and are anatomically shaped to meet esthetic and functional require-ments. (2) The denture body replaces the resorbed alveolar ridge and bears the replacement teeth. The denture body is anatomically shaped to provide support to the cheek and the tongue. It must not impede the tongue or restrict the patient’s speech function. (3) The denture base lies against the mucosa over an extensive area and is relinable; the edges are trimmed in the area of mobile mucosa. 114Removable Partial Dentures• Coupling between the denture and the residual dentition with rigid, semirigid, resilient, and ar-ticulated structural elements• Physical and technical design or retentive ac-tion, in which the spring ttings are in the form of clasps that anchor by spring forces, and tele-scopic components in the form of parallel or conical ttings (eg, telescopic crowns that an-chor by means of friction resistance)Anchorage by means of implants in conjunction with these types of ttings is always a possibil-ity. The implant embedded in the bone serves to carry the primary tting part. Anchorage achieved by the retentive effect of suction, adhesive, and cohesive forces is of limited importance to partial dentures. This is the main form of anchorage for complete dentures because insufcient mechani-cal retentions are available.Design Principles for Denture SaddlesThe design of denture saddles in model cast pros-theses allows for the possibility of relining (Fig 4-12). The denture base should be relinable in the saddle area, where particularly severe tissue shrinkage occurs. This applies generally to the al-veolar ridges, and this area should be interpreted as broadly as possible. It is not enough to make the vestibular part of the ridge relinable, but the possibility of relining should extend just as far lin-gually.The relinability of dentures is necessary main-ly because the edentulous parts of the jaw will shrink in response to pressure loading (or a total lack of loading). If the mucosal support atrophies after a certain period of denture wearing, the poor accuracy of t has to be compensated for by relin-ing. Inaccuracies in the t of the denture saddle lead to horizontal transverse stresses on the jaw segment and hence to increased tissue resorption.Free-end saddles are designed as extension saddles and are always entirely relinable. These saddles are extended onto the largest possible mucosal surface in order to enlarge the support surface and improve distribution of masticatory forces (the snowshoe principle). The saddle en-compasses the maxillary tuberosity in the maxilla and the alveolar tuberosity in the mandible.An extended saddle must be scalloped to avoid ligaments, muscle attachments, and bony ridges, as the need for saddle reduction dictates. The ves-tibular parts of the saddle should not be applied too thickly, in the same way as for lingual parts, so that the space for the tongue is not restricted and the cheeks and lips are not displaced; a valve-type margin, as with complete dentures, is not at-tempted.An alginate impression is taken of the saddle surface while pronounced functional movements are performed to determine the entire surface area of the edentulous section that will be neces-sary for denture wear. An extended alginate im-pression is taken of the sublingual space by the mucostatic impression technique to ensure that sufcient space is allowed for the sublingual bar.Moderate pressure loading on the mucosa by the denture saddle can have a positive or stimu-lating effect on the tissue. It has been observed that unloaded mucosal areas or bony segments undergo inactivity atrophy, whereas alveolar bone that has been loaded with normal pressure by ac-curately tting denture saddles are not subject to anywhere near as much shrinkage (Fig 4-13).The degree of loading and progression of shrink-age are related, but the relationship cannot be de-tected in every case. It is very clear, however, that a jaw that was instantly loaded with an immediate prosthesis after extraction of a number of teeth will display less shrinkage than a jaw that was not tted with a long-term prosthesis until weeks after healing. In particular, this illustrates the prophylac-tic value of an immediate restoration while, gener-ally speaking, pointing to some conclusions about the shrinkage process under denture saddles.The resilience of the periodontium allows a supported prosthesis to sink as far as required for it to stimulate the mucosa. With an accurately t-ting, regularly relined denture, edentulous jaw segments can be sustained for long periods with-out any appreciable tissue breakdown. If a com-plete denture is later tted, the shape of the alve-olar ridge is crucial for the retention of such a restoration; therefore, a well-preserved ridge is always valuable.The tooth-prosthesis interface is the transitional region between denture saddle and abutment tooth, which is particularly at risk in terms of 115Design Principles for Denture Saddlesperiodontal prophylaxis. Saddle contact with the gingival margin in the tooth-prosthesis interface should be avoided to prevent the gingival margin from being squeezed when loaded by the saddle; nevertheless, no retention space should be cre-ated where plaque can accumulate.To this end, the saddle region can be shaped to form a tooth-prosthesis interface from metal framework to anchoring element, without acrylic coverage, which is referred to as a closed-saddle framework or clasp stem arrangement (Fig 4-14).The saddle retention forms the mechanically rm connection between the denture body and the denture framework; it is at a distance from the alveolar ridge so that a uniform denture base can be shaped out of acrylic resin. The saddle re-tention also leaves enough space occlusally for the replacement teeth, under which it is placed FavorableFavorableUnfavorableUnfavorableFig 4-12 Denture saddles must be designed so they can be relined; that is, after a certain wearing period, the dentist must be able to rework the area of the denture with acrylic resin where the alveolar ridge has shrunk. The metal frameworks must be de-signed so that only a small part of the jaw is covered with metal. In the posterior region, only one retention is laid on the middle of the ridge, and the framework parts should not touch the jaw. The more extensively a denture saddle can be relined, the better the construction. In the anterior region, however, it may be necessary to place a bar relatively high to guarantee the denture’s stability. Starting from the bar, retentions and a collar can be tted to the replacement teeth. A lingual plate in the area of a replacement tooth, which is fully relinable, is the best construction. A chemical metal-acrylic resin bond makes more delicate retention designs possible; the relinability of a denture framework is essentially guaranteed by silanization of the framework because the acrylic resin can be directly polymerized onto the organophilic silanization layer.Fig 4-13 Saddle retentions are placed in the middle of the al-veolar ridge, approximately 1 mm from the mucosa; they must not show through from the vestibular side. The border to the abutment tooth adjacent to the gap is kept clear of the peri-odontium and must not provide an edge where deposits can become lodged.Fig 4-14 The closed-saddle framework arrangement has a smooth metal surface without acrylic resin covering the bor-der to the abutment tooth adjacent to the gap. The metal is polished smoothly so that plaque cannot build up. The replace-ment tooth is prepared from the vestibular side and looks like a pontic. 116Removable Partial Denturescentrally. The saddle retention must not show through the saddle acrylic resin vestibularly for esthetic reasons.Design Principles for Denture FrameworksFrameworks for partial dentures can be made from acrylic resin or metal (chromium-nickel, cobalt-chromium, or gold-platinum alloys). The decision regarding which material to use depends on a few fundamental considerations.Acrylic resin frameworks are inexpensive and relatively simple to fabricate. They have to be shaped so that they are thick and cover a large area to ensure adequate stability. For the same reasons, an acrylic resin framework should al-ways t residual teeth closely like a collar, which is problematic in terms of periodontal hygiene. A large framework surface evenly transfers masti-catory forces to the underlying mucosal support. In a severely reduced partially edentulous den-tition, in which adequate periodontal support is impossible and an extended base is in any case required, an acrylic resin framework is an option. Acrylic resin dentures are fully relinable. Howev-er, their drawbacks are poor stability, especially in the area where clasps are attached, and a large, thick shape that makes them unpleasant for pa-tients to wear. Acrylic resin frameworks are there-fore only used for interim prostheses.Model cast dentures made of chromium-nickel alloys are preferable to any acrylic resin denture in terms of functional quality. The metal frame-works can be worked to be very thin and delicate because of the high material strength; narrow connectors or transverse bands are often suf-cient. The individual clasps are joined together rigidly enough by the metallic structure, so that adequate splinting of the residual dentition can be achieved.Patients prefer metal frameworks because they are more comfortable to wear, even if the greater heat conductivity of the metal may have an un-pleasant effect when they eat hot food. Metal frameworks provide better accuracy of t than acrylic resin dentures. Prostheses with metal frameworks can always be relined with acrylic resin in the area of the alveolar ridges and in oth-er areas of the framework after tting of retention components or after application of a silane layer.The delicate metal frameworks are particularly advantageous in the mandible because unfa-vorable spatial relationships often prevail there. Even given the small space available, sufciently stable connectors can be placed that can also be satisfactorily sited in terms of periodontal hy-giene. When constructing model cast dentures, the framework parts should meet the following fundamental requirements (Fig 4-15):• Stable and torsion resistant • Sufciently delicate• Clear of the periodontium• Largely clear of the tongueStability can be achieved by enlarging or strengthening the prole of the framework parts. It is important to nd a practical compromise be-tween the necessary stability and the smallest possible size of framework parts; stable yet deli-cate is the watchword.For sublingual bars in the mandible, prefabri-cated wax proles with adequate dimensions are suitable for waxing up. It is different in the maxil-la, where there are several design options for framework parts. These have to be strengthened by suitable moldings so that adequate resistance to deformation is achieved. Deformation resistance is only adequate if the framework does not warp in response to normal stresses during chewing.The width of a framework part that rests on the mucosa should not exceed 10 mm to avoid deposits. Such a narrow band needs to be rein-forced to 1.5 mm by a molding in the middle to achieve torsion resistance. The wider the band, the smaller the reinforcement needs to be.Periodontal clearance relates to periodontal hy-giene. For this purpose, the edge of the denture framework must be a minimum of 4 mm from the marginal periodontium of the remaining teeth (Fig 4-16). The transition from the framework to the denture saddle should also be fashioned to ensure periodontal hygiene. The tooth-prosthesis interface is kept clear of the periodontium as the framework parts are brought close to the denture saddle in a wide arch, which is mainly necessary at the transition to the anchoring elements (Fig 4-17). 117Design Principles for Denture FrameworksTongue clearance is achieved by delicate shap-ing of the framework parts; thin plate compo-nents overlying the mucosa are better than thick bar proles placed at some distance from the al-veolar ridge. Framework parts should largely be laid outside the range of activity of the tongue, which is the area of the palatine rugae (pressure and fricative eld) in the maxilla and the entire sublingual area in the mandible.Clear of periodontiumClear of tongueDelicate StableFig 4-15 Denture frameworks should be stable and torsion resistant. They also must allow self-cleaning as they are kept clear of the periodontium at a minimum distance from the marginal periodontium. And they must be shaped so delicately that they do not impede tongue activity and are comfortable to wear.Fig 4-16 To avoid the marginal periodontium of the abutment teeth and the residual dentition, framework parts should be placed so that in the tooth-prosthesis interface the marginal areas cannot be damaged by mechanical stress or coverings. Denture frameworks, like the sublingual bar shown here, should be placed a minimum of 4 to 6 mm from the gingival margin. The minor connectors in the tooth-prosthesis interface should leave a gap that allows for rinsing.Fig 4-17 Minor connectors of the framework parts for the closed dental arch (eg, Bonwill clasps) should also be clear of the periodontium. The minor connector must be at a minimum distance from the alveolar ridge and should not impede the tongue; if the connector sticks out too much, it will interfere with speech function.2–4 mm4–6 mm 118Removable Partial DenturesDenture Frameworks in the MandibleDenture frameworks in the mandible are shaped like sublingual bars. The alternatives would be full plates covering the lingual area of the alveo-lar ridge and raised along the teeth in the form of a collar.Lingual plates should be rejected as unsuitable (Fig 4-18). Even though these structures achieve an excellent splinting effect and can thereby sta-bilize the residual teeth, these benets are out-weighed by drawbacks in terms of periodontal hygiene. If a denture ange extends as far as the tooth, it results in dynamic, mechanical irrita-tion of the marginal periodontium; at the same time, this gingival area becomes encapsulated, preventing the necessary self-cleaning. The con-sequences are chronic inammation and the for-mation of deep gingival pockets, which can lead to complete destruction of the periodontium and loss of the tooth. A lingual bar is easy to extend, although admittedly its extension very soon be-comes a necessity.A sublingual bar for mandibular dentures has a rounded, drop-shaped prole; the tip of the drop is tted to the incline of the alveolar ridge and points upward. It must be placed clear of the peri-odontium and tongue and should be worked so it is stable and torsion-resistant but also delicate enough to ensure that it is pleasant to wear. It can be carved out of prefabricated wax prole wires that are 4-mm high and 2.5-mm thick. In contrast to the framework parts that lie against the muco-sa, a sublingual bar must be polished (ie, smooth) in the area facing the mucosa.Owing to the periodontal clearance and clear-ance of the tongue, a sublingual bar is placed as deeply as possible; the marginal-periodontal safety distance is 4 to 6 mm (Fig 4-19). In the ante-rior region, the bar must lie a horizontal distance of 0.2 mm from the alveolar ridge and therefore must not touch the mucosa (Fig 4-20). If the pos-terior alveolar ridge area is inclined in the lingual direction or the inclination of the posterior teeth is very pronounced, the horizontal distance may be increased to as much as 1 mm. If free-end saddles sink under masticatory loading, the sub-lingual bar is pressed forward onto the alveolar ridge. Therefore, freedom of movement becomes necessary so that the vertical alveolar ridge sur-face is not loaded and the bar does not become embedded.The mobile oor of the mouth must not be displaced. The average depth of the oor of the mouth is approximately 3 mm at the incisors, though it may be less at the attachment of the lin-gual frenum and about 6 mm at the premolars. The bar must pass around the lingual frenum so that movement of the frenum and the tongue is not impeded. This makes it difcult to place the bar clear of the periodontium in this area.If the lingual frenum attaches too high or the oor of the mouth lies too high, so that the sub-lingual bar does not maintain the minimum dis-tance from the marginal periodontium, a reason-able distance might be achieved by changing the position of the bar, that is, horizontal displace-ment under the tongue (Fig 4-21). A supracoro-nal transverse connector may also be placed that runs along the dental crowns of the groups of re-sidual teeth, or the framework could be placed as a vestibular connector in the oral vestibule.Fig 4-18 Lingual plates should be re-jected in principle because they cause encapsulation at the marginal periodon-tium. To avoid a mechanical impact on the periodontium, the edge of the plate is trimmed slightly, which gives rise to nich-es in which deposits will form. As self-cleaning is prevented, chronic inamma-tion develops, deep gingival pockets are formed, and complete destruction of the tissues supporting the teeth and loss of the teeth may occur. 119Denture Frameworks in the MandibleThe minor connectors to the anchoring and supporting elements also have to be constructed so that a minimum distance of approximately 4 mm from the periodontium is achieved in or-der to allow for self-cleaning (Fig 4-22). If minor connectors from the denture framework to clasp structures are prepared, problems of periodontal hygiene may arise.With these structures, it is important to ensure that the horizontal distance is not less than 5 mm from the saddle and that the difference between two connector parts is the same amount. A struc-ture in which continuous splinting is combined with a bar connector—always in the approximal areas—should be rejected if this means the bar would still run at a distance of 2 mm from the marginal periodontium. This structure is only ex-ceeded by a lingual plate in its deleterious effect.4 mm6 mm0.2 mm2 mm4 mm4 mm4 mmFig 4-21 To achieve an adequate safety distance from the marginal periodontium, the bar can be placed horizontally un-der the tongue if the oor of the mouth is too high. Fig 4-22 If the safety distance from the periodontium is not observed, self-cleaning is prevented and deposits will form. If a sublingual bar becomes embedded, the mucosa will be squeezed, swell up, and become inamed.Fig 4-19 In the mandible, a sublingual bar should run approxi-mately 0.2 mm from the alveolar ridge. This distance may be increased to around 2 mm in the posterior region if the bar cannot be taken out because of the inclination of the alveolar ridges and teeth. The vertical safety distance from the marginal periodontium is 4 mm in the anterior region and 6 mm in the posterior region.Fig 4-20 The sublingual bar is drop shaped. The minimum dis-tance from the alveolar ridge is 0.2 mm. If the alveolar ridge is upright, the bar can be taken out without being obstructed. If the alveolar ridge is inclined lingually, the horizontal distance is increased; the bar can be shifted to the vestibular aspect if the inclination of the alveolar ridge is extreme.4 mm 4 mm 4 mm 120Removable Partial DenturesDenture Frameworks in the MaxillaDenture frameworks in the maxilla need to be shaped to ensure clearance from the periodon-tium, tongue, and palate as well as stability and torsion resistance (Fig 4-23); they have to be deli-cate to make them pleasant to wear.A full plate, as prepared for acrylic resin den-tures, can be used for complete dentures. For a partial prosthesis, a full plate is only necessary in a reduced form if one or two residual teeth are still present. In this case, the extensive mucosal sup-port is intended to absorb the masticatory forces; for this purpose, supporting elements in the form of resilient anchors are usually prepared. Starting from a full plate covering the whole palate, three types of framework can be derived:• Anterior palatal strap• Posterior palatal strap• Skeleton plateAn anterior palatal strap is also known as a horseshoe connector or a sectioned plate. The framework is modeled out of 0.5- to 0.8-mm-thick grained wax, and the curved posterior edge of the strap can retain a prepared reinforcement ap-proximately 0.2 mm deep; the width is between 15 and 20 mm, depending on the size of the teeth being replaced and the thickness of the strap. The torsion resistance of an anterior palatal strap is adequate at these dimensions.A horseshoe design is indicated if both anterior and posterior teeth have to be replaced. When only the posterior teeth are missing, a horseshoe connector may be necessary if the palate in the posterior area has an excessively pronounced palatine suture or a sturdy palatine torus. A horseshoe connector can be prepared for an arch with missing posterior teeth in such a way that extensions can be made later if anterior teeth be-come inadequate.The pressure and fricative eld of the palate is covered by an anterior palatal strap (Fig 4-24). This impedes the function of the tongue in terms of speaking as well as turning and insalivating food. The wearing properties are therefore unfa-vorable.A posterior palatal strap, which may also be called a transverse strap or transpalatal bar, lies in the posterior area of the palate approximately 3 mm in front of the palatal vibrating line. The thickness of a posterior palatal strap depends on the length and path of the strap. If a pointed, high palate has to be restored, the transverse connec-tor must be thicker and fashioned over a broad area. For a at, narrow palate, the transverse con-nector can be relatively thin. The width ranges be-tween 12 and 18 mm; it is modeled out of 0.5- to 0.8-mm-thick grained wax and reinforced in the middle with a 0.8-mm-thick inlaid strip like the ridge of a roof; as a result, this palatal strap is suf-ciently torsion resistant and does not become embedded.A posterior palatal strap is indicated if posterior edentulous spaces have to be treated; to restore a posterior edentulous gap and a free-end gap, the palatal strap must be wider and thicker so that masticatory forces can be transmitted to the mu-cosal support.The tongue is left clear because the whole pres-sure and fricative eld is uncovered (Fig 4-25); thus, the posterior palatal strap has the best wear-ing properties. However, this type of framework is not suitable for extensions in the anterior region.A skeleton plate (ring-shaped connector) com-prises two slender palatal straps in the posterior and anterior area of the palate (Fig 4-26). The thin bars must have a certain minimum width (5 to 10 mm) and minimum thickness (prole strip in the middle that is 1 to 3 mm). This kind of denture framework has the best torsion resistance.A skeleton plate is indicated for alternating edentulous gaps when a periodontally supported interdental insertion prosthesis needs to be fabri-cated. No forces can be transferred to the muco-sal support with skeletal frameworks. Therefore, they are only suitable for cantilever xed partial prostheses if the posterior palatal band is wid-ened, and in that case, this type of framework can be used universally.In terms of framework dimensions, a framework can be kept smaller the more extensive the peri-odontal support of the denture. In other words: The fewer residual teeth that are available as abutments, the larger the area the denture base (the framework) has to cover. A skeleton plate covers little of the natural palatal surface, tongue function is only slightly restricted, and wearing properties are very favorable. 121Denture Frameworks in the MaxillaFig 4-26 A skeleton plate made of slender, proled palatal straps leaves wide areas of the palate uncovered. The delicately sectioned plate is only used for interdental saddles.Fig 4-23 There are three basic re-quirements when shaping the frame-work parts for model cast dentures: stability, periodontal clearance, and tongue clearance. In the maxilla, ad-equately stable framework parts can be reduced from a full plate to create three different forms: anterior pala-tal strap, reduced anteriorly; poste-rior palatal strap, reduced posteriorly; and skeleton plate, reduced from the middle.Fig 4-24 An anterior palatal strap (or horseshoe connector) lies in the anterior part of the palate and cov-ers the pressure and fricative eld. Interdental and free-end saddles can be connected with a horseshoe con-nector.Fig 4-25 A posterior palatal strap connects two denture saddles in the halves of the dental arch in the poste-rior part of the palate and leaves the pressure and fricative eld clear. 122Removable Partial DenturesAnchoring and Supporting ElementsRemovable partial dentures belong to the group of fully removable tooth replacements and are therefore anchored to the residual dentition with detachable connectors. The anchoring elements also provide support on the residual dentition, forming integrated anchoring and supporting ele-ments that are described as a unit.Mechanical ttings are used as anchoring and supporting elements. There are two types based on their functional principle: (1) resilient (or elas-tic) and (2) telescopic designs, which can be fash-ioned by hand or industrially (prefabricated com-ponents).Resilient structural elements anchor by means of spring forces and are used in the following types of designs (Fig 4-27):• Hand-fabricated• Bent-wire clasp• Cast onlay clasp• Industrially fabricated• Resilient circumferential anchor (eg, Rothermann attachment)• Stud anchor with spring sleeve• Stud anchor with spring head• Resilient bars (eg, Dolder bar)The functional value of resilient anchoring ele-ments is dened by their splinting effect; resilient components offer semirigid connections that pro-duce statically indeterminate systems depending on design.The principle of a spring t is demonstrated by an elastic ring that is open on one side and cor-responds to the basic structure of a double-arm clasp. Such a ring widens with the pitch of the cone when it is pushed over a conical shaft. The restoring force of the widened ring resists being pushed onto the cone. The ring springs back into its original shape when, for example, a match-ing groove is set into the cone or when the clasp is pushed over the widest circumference of the tooth into the undercut area.The retentive or extraction force of a resilient structural component arises when the spring ele-ment is bent apart on an inclined plane; the spring force does not act in parallel to the direction in which the spring element is withdrawn but occurs as slope force and frictional force on the inclined plane.Telescopic anchors are precision structural com ponents in the form of parallel or conical t-tings that gain their joining and separating forces or retentive and extraction forces from static and dynamic friction resistance. The following types are common:• Hand-fabricated • Telescopic crowns• Channel-shoulder(-pin) attachments• Circular notch with shear distribution arm• Milled parallel bars• Bolts• Industrially fabricated• Precision attachments• Bar attachments• Bolt attachmentsThese structural elements have two compo-nents: the primary part and the secondary part. The primary part is xed to the residual dentition as a subcrown (in the case of telescopic and ta-pered crowns) or as the primary matched part of an attachment soldered or cast onto an abutment crown. The secondary part, either the telescopic or tapered crown or the secondary attachment com-ponent, is located on the removable restoration.Prefabricated matched components, produced by computerized manufacturing methods with specialized tools from high-quality materials with high precision and within dened tolerances, ful-ll the different functional requirements within technically dened tolerances, depending on the design. Prefabricated components are engaged in normal-size anatomically shaped crowns or tted interproximally. Extracoronal components are questionable in terms of periodontal hygiene; they can cause mucosal irritation due to plaque, suction, and the compressive effects of the oat-ing denture parts.In the case of manually fabricated components, the primary part is produced by the milling pro-cess and the secondary part is waxed up and cast with tting tolerances that cannot be calculated. Fabrication of the secondary part by the galvano-plastic technique yields higher accuracy of t. To ensure the dened retention, interlocking com- 123Anchoring and Supporting ElementsRetention by spring forcesRetention by static and dynamic frictionManual fabricationIndustrial fabricationBent wire clasps for temporary restorationCast onlay clasps with calculable spring forcesResilient circumfer-ential anchor (after Rothermann) as root crown anchorStud anchor with spring retention sleeve as crown anchorStud anchor with dened spring forces as additional anchorageDolder spring bar as resilient bar anchorageTelescopic crown for combined dentureTelescopic half-ring with spring pinsEncircling notch with load distributor as stabilizer for precision attachmentBar attachment manually and indus-tially fabricatedPrecision attachments of different designs for universal useBolt and bolt attach-ment with replaceable worn partsFig 4-27 Types of anchoring and supporting elements. 124Removable Partial Denturesponents can be inserted that lock the telescopic components in the resting position.Function of Anchoring and Supporting ElementsAnchoring and supporting elements must anchor the denture securely during speaking and chew-ing and must transfer the functional forces, in a largely tissue-protective way, to the denture rest area comprising the periodontium and mucosal support. Anchoring and supporting elements need to meet the following requirements:• Fulll a retentive function• Secure the vertical position• Secure the horizontal position• Brace the residual dentition• Ensure periodontal hygieneRetentive function means securing the den-ture against extraction forces during functioning, which can occur due to sticky foods, the denture’s own weight, and tongue and cheek movements when speaking. The extraction forces must be periodontally tolerable and must not exceed a maximum of 10 N.Securing the vertical position concerns the periodontal support, whereby functional forces acting on the denture are distributed centrically to the periodontal tissues. Eccentric loading of abutment teeth must be avoided because this can cause faulty loading of the abutment periodon-tium and give rise to uncontrolled detachment of the denture from the residual denture, which non-physiologically loads the mucosa.The occlusal rests secure the vertical position when cast claps are used. In the case of milled components, occlusal or cervical shoulder milling fullls this function. Prefabricated components have depth stops to limit vertical movement.Securing the horizontal position involves ab-sorbing sagittal and transverse thrusts. The den-ture can be shifted, twisted, or tilted by functional forces on the mucosal support (Fig 4-28). These denture movements are supposed to be absorbed by anchoring and supporting elements and trans-ferred to the abutment teeth. Securing the posi-tion against horizontal thrusts produces eccentric loading on the abutment teeth.There is an interaction between mandibular movement under tooth contact and the thrust moments on the denture. When the mandible moves forward, a maxillary prosthesis is pulled in the same direction, and a mandibular denture is pushed distally.Fig 4-28 A support line that intersects the denture body be-comes the axis of rotation of the denture; the denture will al-ways rock. In the process, the remaining teeth are moved to and fro so that they are soon lost. 125Function of Anchoring and Supporting ElementsIn the case of clasp anchors, the horizontal posi-tion is secured by the rigid enclosing parts (clasp body and clasp bracing section). In telescopic de-signs, the rigid connector braces against horizon-tal thrust; spring anchors, on the other hand, will secure position inadequately (Fig 4-29).Bracing the residual dentition concerns the as-pect of stabilizing the residual dentition that has been rendered unstable due to reduction, as an-choring and supporting elements distribute the vertical and horizontal loads evenly to the residu-al dentition and prevent eccentric movements of the abutments. The residual dentition is braced when the remaining teeth are splinted by groups of clasps or by rigid telescopic components. This fullls the therapeutic function of the restoration.Splinting by enclosing the teeth in groups of clasps is elastic and still permits abutment tip-ping. The elastic splinting effects allow approxi-mate tooth movements as they are required in the closed dental arch for forces to be uniformly distributed.The abutments are interlocked with telescopic components that absorb all stresses as a closed unit. Rigid interlocking moves all the abutments at the same time when loaded; all the abutment periodontal tissues form a resistance block (Fig 4-30).The prophylactic function of prosthodontics should ensure periodontal hygiene. The anchor-ing and supporting elements must attach to the abutment teeth without causing mechanical dam-age or nonphysiologic loading.Cast clasps lie relatively broadly on the tooth surface and abrade dental tissue during function-ing; they form retention sites for plaque and pro-mote caries lesions. With their minor connectors, they cover the gingival margin, possibly irritating it mechanically or leading to encapsulation.Fig 4-29 The enclosure provided by clasps is effective at bracing the denture against horizontal forces; the lower arms of the clasp are inadequate for counter-acting these forces. If all the clasps in the maxilla are opened mesially, the denture is not secured against distally directed thrusts. This applies to a mandibular den-ture in which all the clasps are opened distally, which means mesially directed thrusts cannot be absorbed.Fig 4-30 When splinted (interlocked), all of the involved teeth are combined by the denture structure to form a resistance block. In this rigid connection, all of the teeth absorb the masticatory pressure applied. Periodontally damaged dental arches can be therapeutically treated by splinting structures. A distinction is made between primary splinting, in which the interlocking effect is achieved by a bar construction, and secondary splinting, in which the rigid connection is achieved by a partial denture anchored with tele-scopic supporting elements. 126Removable Partial DenturesConnecting the Denture to the Residual DentitionA removable partial denture should allow full chewing function while transmitting the mastica-tory forces to the residual dentition and bases of the dental arch, yet largely sparing the denture rest area. The resilient edentulous jaw segments are less suitable for absorbing masticatory forces than the remaining teeth because of the peri-odontal ligament’s low tolerance of movement. If, in addition, the mucosa is compressed by in-termittent denture movements, the result will be progressive resorptive atrophy of the alveolar bony tissue.The anchoring and supporting elements must join or couple the denture to the residual denti-tion on a tissue foundation in such a way that the denture gains adequate positional stability and physiologic transfer of masticatory forces to the periodontium and tegument is ensured. Follow-ing are the four states of coupling between the denture and the residual dentition:• Rigid coupling• Semirigid coupling• Articulated coupling• DecouplingRigid coupling with telescopic or locking an-choring and supporting elements completely se-cures the vertical and horizontal position of the prosthesis (Fig 4-31). Rigid coupling is statically determinate, can transfer all the masticatory forc-es to the abutment teeth, and will not load the mucosa and the bony foundation. To achieve this, as many abutment teeth as possible must be in-corporated into the coupling; the more residual teeth are connected by rigid anchoring—thus, the more extensive the xed denture support—the better the coupling state.Rigid coupling cannot be implemented on a clasp prosthesis. Instead, rigid telescopic anchors are needed. These include not only prefabricated attachments but also handmade telescopic or ta-pered crowns and their modications; combina-tions of prefabricated and handmade structural components also provide the intended coupling.If the residual dentition is insufcient for com-plete periodontal support, conditionally rigid cou-pling can be achieved with resilient attachments. These telescopic components have a dened depth stop that allows the denture to lie in the resting position, initially on the mucosa. Not until the resilience of the mucosa is exhausted by ex-posure to masticatory pressure, and the denture has sunk onto the depth stop, will axially directed forces be absorbed by the periodontium of the abutment tooth.Semirigid coupling arises with prostheses that are xed to the residual dentition with cast onlay clasps (Fig 4-32). The horizontal and vertical posi-tions are not fully secured with clasps, and mas-ticatory forces are transferred to the periodontal tissues of the abutment teeth and to the mucosa. Interdental insertion prostheses will secure the position effectively because all the saddles can be periodontally supported and the abutment teeth can be splinted (Fig 4-33). Cantilever xed partial dentures must be supported on the remaining teeth, but equally on the mucosa.Mixed seating of cantilever xed partial den-tures is statically indeterminate because the peri-odontal rest area is rather rigid and the mucosal support is very yielding. True distribution of load between the periodontium and the mucosa can-not be achieved; and in addition to uneven load-ing of the resilient mucosa, nonphysiologic load-ing of the periodontium occurs. To reduce the load on the mucosa, groups of clasps are extend-ed onto the residual dentition. If the free-end sad-dle sinks in response to masticatory loading, the entire clasp unit will counteract this sinking.Articulated coupling exists in a cantilever xed partial denture that is supported with proper joints or spring connecting parts (Fig 4-34). Such a system also has the static indeterminacy of a mixed seating, in which the periodontal rest area can be viewed as rigid and the mucosal support as a resilient rest. Furthermore, the mucosal rest area is loaded considerably at its distal end but not at all under the joint, thus lying in the pres-sure shadow.Decoupling happens in a denture without an-choring and supporting elements on the residual dentition. This kind of prosthesis rests on the mu-cosa, which absorbs all the compressive, tensile, shearing, and tipping forces. The denture may 127Connecting the Denture to the Residual DentitionFig 4-31 Rigid coupling between the denture and the residual dentition can be produced with rigid attachments; secondary splint-ing of the in volved abutment teeth ensues.Fig 4-32 Physically encompassing the rigid clasp parts of double-arm clasps with onlays in the case of interdental saddles offers only semirigid coupling; this produces splinting effects for teeth with clasps.Fig 4-33 If a free-end saddle is joined to the residual dental arch via rigid connectors, rigid coupling occurs, by which the vertical and horizontal positions are fully secured. Joining sev-eral teeth to the rigid connecting element via splinting can fully compensate for masticatory forces. The abutment teeth are axially loaded and slightly tipped. 128Removable Partial Denturestilt, twist, shift, or tip because no bracing of the horizontal and vertical position is provided. Po-sitional stability has to be achieved by tooth po-sition and extension of the base, as in complete dentures, and bar connectors cover the marginal periodontium and broad mucosal areas and lead to tissue irritation due to encapsulation, plaque, suction, and compressive effects. Certain tech-nical instructions for anchoring and supporting elements and criteria for assessing their quality can be deduced systematically from the general requirements.Fig 4-34 Articulated coupling between a free-end saddle and the residual dentition can be achieved by proper hinge joints, which results in extremely uneven loading of the mucosa. Similar conditions prevail with elastic coupling achieved with a double-arm clasp with onlay. Once again the mucosa is loaded extremely unevenly.

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