THE JOURNAL OF PROSTHETIC DENTISTRY BUDTZ-JORGENSEN AND BOCHET

Alternate framework designs for removable partial dentures

Ejvind Budtz-Jorgensen, DDS, Dr Odont,a and Gilbert Bochet, Dr Med Dentb
University of Geneva, Geneva, Switzerland

Statement of problem. The removable partial denture is usually less appreciated than the fixed partial
denture by both patients and prosthodontists. This negative attitude could be due to problems associated
with the wearing of a removable partial denture and concern essentially with comfort, esthetics, mastica-
tory function, occlusal stability, and maintenance of oral hygiene. Such problems could be limited if
treatment planning is made carefully, according to simplified and logical principles for framework design,
and if oral hygiene and the fit of the dentures are regularly controlled.
Purpose. This article reviews the factors associated with the prognosis of treatment with removable partial
dentures. Furthermore, the article describes framework design applied in different clinical situations and
compares them with more conventional designs. It seems important to consider a framework design that
privileges comfort, esthetics, and oral hygiene rather than to follow mechanical rules that are entirely
theoretical and have not been confirmed scientifically or clinically. (J Prosthet Dent 1998;80:58-66.)

CLINICAL IMPLICATIONS
Framework designs for removable partial dentures are suggested that emphasize sim-
plicity, esthetics, patient comfort, and oral hygiene.

W hen planning treatment for partially edentu-

lous patients, the dentist is confronted with myriad com-
have a functional or esthetic need for replacement of
posterior teeth (Applegate-Kennedy classification class
binations of edentulous spaces and remaining teeth. In I and II). An RPD is also an excellent treatment modal-
making the framework design, the dentist must consider ity in class III situations with large tooth-supported den-
the patient’s comfort, esthetics, biomechanics of the ture bases, where it is difficult to provide sufficient re-
prosthesis, and the prognosis of the abutments. In addi- tention and stability for a fixed partial denture (FPD).
tion, the concept and design of the denture could have Class IV and V RPDs are indicated particularly when
an impact on the incidence of mechanical failures of the the edentulous space is too large for a fixed prosthesis
framework. Finally, proper evaluation of the actual den- or when alveolar bone loss has been sustained that re-
tal and periodontal situation, periodontal treatment, quires a resin flange to replace the missing bone to sup-
maintenance of good oral hygiene, and regular port the middle third of the face.
postinsertion controls are also of major importance in In patients who have lost their posterior teeth (short-
minimizing the sequelae associated with wearing remov- ened dental arches), a major benefit of wearing an RPD
able partial dentures (RPDs), such as caries, progres- is improved masticatory performance.1,2 However, sat-
sion of periodontal disease, and residual ridge resorp- isfactory oral comfort defined as absence of signs of
tion. craniomandibular dysfunction, nonimpaired chewing
This review article outlines biologic consequences of ability, and absence of complaints regarding the appear-
wearing RPDs and suggests guidelines for framework ance of the dentition is often the situation in patients
design that consider simplicity, esthetics, biomechanics, with shortened dental arches.3,4 Furthermore, a situa-
and patient comfort. tion with shortened dental arches is not a risk factor for
developing craniomandibular dysfunction but is usually
INDICATIONS associated with long-term oral comfort.5 On the con-
Treatment with RPDs is a noninvasive and low-cost trary, wearing RPDs in this situation often gives rise to
solution for the prosthetic rehabilitation of patients who complaints related to impaired esthetics and oral com-
fort,6 and may be to such a degree that patients often
a
decide not to wear the denture.7-9 In addition, the com-
Professor and Chair, Division of Gerodontology and Prosthodontics,
Section of Dental Medicine. fort of having a FPD largely surpasses that of wearing a
b
Assistant Professor, Division of Gerodontology and Prosthodontics, RPD.2,10 Therefore treatment with RPDs should only
Section of Dental Medicine. be considered when manifest functional indications are

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present and treatment with FPDs is not possible for bio- of this article is to suggest framework designs that may
logic or financial reasons. In this article, some principles reduce the risks associated with wearing RPDs.
of framework design are outlined that could help to
minimize the complaints associated with wearing
PROGNOSIS: BIOMECHANICAL AS-
RPDs.11-13 PECTS
Major complications of treatment with RPDs are
PROGNOSIS: PERIODONTAL ASPECTS
mechanical failures such as fractures of major or minor
AND CARIES
connectors and occlusal rests and deformation or frac-
The main disadvantage of RPDs is the risk of local ture of retentive clasps.28,35-37 Furthermore, the resorp-
damage to the remaining teeth and their supporting tis- tion of the residual ridge under extension bases and wear
sues, mainly as a result of increased plaque accumula- of denture teeth may result in a destabilization of the
tion, caries, periodontal disease, and where applicable, denture and the occlusion.8,28 Thus, for extension base
resorption of the residual ridge supporting the partial RPDs, placement of clasps anterior to the fulcrum line
denture.14-17 However, it should also be realized that (FL) could result in their deactivation or fracture. In
treatment with FPDs may induce a risk for the abut- patients who wear a complete maxillary denture and a
ments and that caries is the most frequent cause of fail- class I mandibular RPD, the consequence may be severe
ure.18 resorption of the maxillary anterior ridge, due to the
In experimental situations, wearing RPDs without oral “combination syndrome.”38 Such technical and occlusal
hygiene caused significantly increased plaque accumu- complications can, to a large extent, be controlled with
lation over not wearing the dentures, in particular on regular relining or occlusal correction.
abutment surfaces.19,20 Periodontal health variables such According to longitudinal studies, the half-life of con-
as gingival inflammation, pocket depth, and gingival ventional RPDs with a cast cobalt-chromium framework
recession were more severe in RPD wearers compared is about 10 years.7,8,12,39 Failure of RPD castings during
with controls.16,21,22 In patients with poor oral hygiene service depends on dimensions and design of the cast-
or very old and ill-fitting dentures, the periodontal con- ings as stress concentrations occur in regions of abrupt
ditions of the abutments were particularly poor, com- change in cross-sectional areas.36 The frequency of frame-
pared with the condition of the nonabutments.17,23 In a work failure also depends on the forces created during
longitudinal study over 3 years, the degree of gingival masticatory function and is especially high when the
recession was shown to be related to the initial gingival denture is opposing a natural dentition.40 From a clini-
recession and the wearing of dentures.24 This study did cal experiment that used rosette strain gauges to record
not demonstrate an influence of denture design (resin the functional deformation patterns of RPDs, it was con-
or metallic RPD, mucosa or tooth-supported bases). cluded that a better distribution of the forces was ob-
However, the dentures were generally designed without tained with a rigid major connector and precise contact
considering the periodontal tissues. Other studies have between the framework and the teeth, namely, occlusal
indicated more severe gingival tissue reactions when the rests, reciprocal clasp arms and guiding planes.41
gingiva was covered by the denture; whereas, an open It is assumed that a distal extension RPD may be po-
space design of minor connectors was less conducive to tentially harmful to the periodontal tissues of the abut-
increases in crevicular temperature, plaque accumula- ments when the extension base is occlusally loaded as
tion, gingival inflammation, and pocket depth.7,25,26 the abutments may be exposed to a distal torque or hori-
Longitudinal studies have reported that wearing RPDs zontal forces. A review of literature on periodontal prob-
is not associated with any deterioration of the periodon- lems associated with the use of distal extension RPDs
tal status provided that good oral hygiene is main- concluded that there was no evidence from clinical stud-
tained.12,27 However, root caries is often a problem, even ies that torquing forces transmitted to the abutments is
in patients with relatively good oral hygiene.28,29 The a serious risk factor for treatment with RPDs.31 Regard-
reason is probably that wearing RPDs predisposes one ing the position of the occlusal rest in extension base
to high salivary levels of mutans streptococci and yeasts.30 RPDs, there is a theoretical advantage of a mesial versus
A comprehensive review of the literature on the peri- a distal placement: anterior position of the FL, reduc-
odontal problems associated with wearing RPDs stressed tion in need of indirect retention, and increased resis-
that the concept and the design of the dentures were of tance to distal displacement of the denture.42 However,
minor importance compared with postinsertion controls laboratory and clinical studies indicate that the risk of
and maintenance of good oral hygiene.31 Furthermore, abutment displacement or increased tooth mobility is
there is no proven any relation between the design of not significantly increased by the placement of distal
the denture and the prognosis of the abutments.32 How- rather than mesial rests.43-47 That the placement of the
ever, it should be stressed that any coverage of gingival rest is of minor importance is reflected in a study on
areas adjacent to abutments may have a detrimental ef- partial denture designs for a Kennedy class II modifica-
fect on their periodontal status.7,20,25,33,34 One of the aims tion 1 case made by dentists in Health Service Practice

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in the United Kingdom.48 Thus, in relation to the ex-

tension base RPDs, a distal rest was used as often as a
mesial rest, despite the established view on load distri-
bution to abutments recommends a mesial rest.49 This
might indicate that aspects other than load distribution,
such as patient comfort, occlusion, and design simplic-
ity, are often taken into account by the practitioner.
The rationale for attempting to reduce or avoid torqu-
ing or horizontal forces acting on the abutments is based
on the hypothesis that these forces may exceed the physi-
ologic tolerance of a normal periodontium. However,
in two recent publications biomechanical considerations
seem to have excessive influence on the concept of RPD
designs.50,51 If rest seats are prepared in the anterior teeth
so resultant forces are directed to the long axis of the
abutment, it is not evident why “the major problem with
dual-path of insertion RPDs of the maxilla is the buccal
migration of the abutment—a canine with a rest but no
clasp”50; and why in Kennedy-Applegate class V “the
remaining anterior teeth cannot be used as abutments
for a RPD if labial reciprocating bracing elements are
omitted for esthetic reasons.”51
From our point of view, the concept in RPD design
should rely on simplicity, secure esthetics, comfort, and
occlusal stability, and should consider oral hygiene. To
reduce the negative effects of wearing RPDs, the fol-
lowing guidelines for denture design are suggested:
1. The dentures should be designed with embrasure
spaces between abutments and bases to reduce plaque
accumulation in the dentogingival area.11,13,52,53
2. To prevent technical failures and to distribute the
occlusal forces, dentures should be designed with rigid
major and minor connectors, reciprocating clasp arms,
and occlusal rests.25,41
3. Occlusal and lingual rests should be placed in well-
prepared rest seats in such a way that the tilting of the
abutment will not take place.
4. To promote periodontal health and the patient’s
comfort, minor connectors should be placed proximally
and, if possible, should contact the edentulous ridge
approximately 3 mm from the tooth surface.11
5. In Kennedy class I and II situations, the denture
Fig. 1. Two RPDs show framework designs (black), fulcrum should be designed for esthetic and mechanical reasons
lines (FL) and diagonals of retention (DR, DR1, DR2). A, Typical in such a way that appropriate retention is achieved with
framework design following RPD principles used by dental two retentive clasps and that there are no retentive clasps
school, University of Geneva, according to principles used opposite the FL.13
circa 1988. No rest on left maxillary lateral incisor and Bonwill
crib or clasp on right maxillary first and second molars to
CONCEPTS OF FRAMEWORK DESIGN:
resist rotational movement around FL. DR also shown, and STATIC-DYNAMIC, BIOLOGIC, ESTH-
hatched gray surfaces of figures correspond to support avail- ETIC, AND COMFORT CONSIDER-
able for RPDs. B, Our design according to current principles ATIONS
of framework design used at University of Geneva dental
school. Lingual rest has been placed on left maxillary lateral Static-dynamic concepts of framework design consider
incisor, which allows RPD to be entirely tooth-supported. Draw- the distribution of the vertical and horizontal forces be-
ings show framework design of retention and rests on right tween abutments and between the abutments and mu-
maxillary first molar and left maxillary lateral incisor provide cosa and what precautions to take not to overload the
indirect retention. periodontal membrane of abutments and to maintain

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Fig. 2. Framework designs (black) show fulcrum lines (FL) and diagonals of retention (DR).
Hatched gray surfaces indicate support available for RPD. A, Stress-releasing clasp system
design for class I RPD according to Ben-Ur et al.56 and following the principles of Kratochvil.54
Bracing is obtained by mesial rest and distal plate and retention by I-bar clasp (RPI). FL and DR
are nearly superimposed. B, In our simplified design, interproximal minor connectors have
been removed and occlusal rests and bracing clasp arms have their origin from distal minor
connector. FL and DR are nearly superimposed, as in A. C, Biomechanical, fail-safe design,
clasp placed on second premolar. Mesial placement of occlusal rest, preparation of lingual
and distal guide plane with lingual bracing and distally placed minor connector. When denture
base is loaded (F), denture can rotate around FL connecting mesial rest of second premolar
without exerting torquing forces on abutment, as bracing arm, shoulder of retentive arm, and
minor connector are on survey line (SL). They do not touch occlusal to SL.

functionally stable dentures. Biologic concepts of frame- contemporary article, a textbook, or was used until re-
work design have been established to minimize harmful cently in our dental school. The B design is our sug-
long-term effects of wearing RPDs, such as caries or gested design. The modifications have been introduced
periodontal tissues. The esthetic considerations in frame- to give greater consideration to oral hygiene, biome-
work design are mainly concerned with keeping parts of chanics and patient comfort.
the framework out of sight. Considerations with regard
Example 1
to patient comfort aim at designing dentures without
rocking movements during function, which do not trap Figure 1, A, represents a typical maxillary framework
food or irritate the tongue. designed at the dental school of the University of Geneva
Framework designs for six clinical situations are pre- according to the principles in use in the late 1980s. The
sented. The A design in each example is taken from a denture comprises two bases, an entirely tooth-supported

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tooth-supported denture base or as a consequence of

residual ridge resorption. A Bonwill clasp has been placed
on right maxillary first and second molars with the prin-
cipal purpose to resist this rotational movement. Whether
this is possible is quite hypothetical, considering the
masticatory forces versus the retentive forces of the
Bonwill clasp.
Figure 1, B, represents a simplified design for the RPD
shown in Figure 1, A, according to the current design
principles actually used by the dental school at the Uni-
versity of Geneva. A lingual rest has been placed on left
maxillary lateral incisor after preparation of a shoulder-
shaped rest seat so that the chewing forces will be trans-
ported along the axis of the tooth. Accordingly, the den-
ture bases are entirely tooth-supported. The DR has an
optimal position with regard to the denture-supporting
area, the rests on the right maxillary first molar and left
maxillary lateral incisor providing support and indirect
retention. All minor connectors are placed proximally
to ensure patient comfort and proper relief of the gin-
giva, and no interproximally placed minor connectors.
Example 2
Figure 2, A, represents a stress-releasing clasp system
design for distal extension RPDs as suggested by
Kratochvil54 in 1963, later by Krol55 in 1973, and re-
cently discussed by Ben-Ur et al.56 in 1996. This was
named the RPI clasp and uses a mesial rest that acts as
fulcrum, and an I-bar direct retainer positioned near the
Fig. 3. Framework designs (black), sketch shows fulcrum line distal extension base. The minor connector of the me-
(FL) and diagonals of retention (DR). Hatched gray surface sial rest acts along with the distal proximal plate as the
shows support available for RPD. A, Kennedy-Applegate class element of reciprocation, as they cover the mesiolingual
II RPD according to Davenport et al.58 FL is placed posteriorly and the distolingual angles of the abutment, respectively.
to DR with risk of deactivation of retentive clasp. There are The axis FL of the RPD and the diagonal of retention
three interproximally located minor connectors. B, Modified
(DR) are placed almost in the same position. Thus, when
design (by E.B-J. and G.B.) provides for occlusal rest on right
functional forces are applied to the distal extension base,
mandibular first molar and cingulum rest on left mandibular
canine to provide indirect retention. FL and DR are close to the torquing effect on the clasped teeth will be minimal.
each other. This design requires only one interproximal minor However, the inconvenience of this design is that the
connector, rather than three. minor connectors and clasp arms are crossing the gin-
giva, which could predispose to increased plaque accu-
mulation. The interproximal placement of the minor
base that replaces the right maxillary premolars and a connectors could compromise patient comfort and, if
mucosa/tooth-supported base replacing the left maxil- the residual ridge resorbs a rotational movement of the
lary canine, premolars, and first molar. In the following denture, may cause the minor connectors to impinge on
examples, the hatched portion of the figures corresponds the gingival tissues.
to the denture supporting area available for the RPD. Figure 2, B, illustrates a simplified design for the frame-
The left maxillary lateral incisor has not been used as work of the RPD in Figure 2, A. The minor connector is
abutment because a lateral incisor is supposed to have placed distally and continues in a reciprocating clasp to
insufficient periodontal attachment to act as an abut- join the rests placed mesially on the left mandibular sec-
ment. The diagonal of retention (DR1) represents the ond premolar and the right mandibular canine, respec-
connecting line between the principal retentive clasps tively. A guide plane has been prepared on the lingual
on right maxillary canine and left maxillary second mo- surface of the premolar for the reciprocating clasp arm.
lar. With this placement, adequate direct and indirect As the FL and the DR are practically in the same posi-
retention is secured. The axis FL indicates the FL or tion, the denture base rotates around the FL without pro-
natural rotation axis around which the denture will tend ducing torquing forces as with a RPI clasp,54-56 but with a
to rotate when force is applied to the large mucosa/ smaller freedom angle, however sufficient, even if the

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extension denture base sinks into the mucosa 1 mm or

more.57 This rotation is possible only if the bracing arm,
the shoulder of the retentive arm, and the minor connec-
tor are on the survey line or gingival to it. A more impor-
tant rotation of the denture could take place if the den-
ture base is not rebased regularly to compensate for the
residual ridge resorption (Fig. 2, C). The rests on left
mandibular lateral incisor and right mandibular first pre-
molar provide indirect retention. This design has the same
advantages from a mechanical point of view as that shown
in Figure 2, A. In addition, it is designed without minor
connectors or clasps with close contact to the gingival
areas that could provide food traps, promote plaque ac-
cumulation, or impinge on the gingival tissues.
Example 3
Figure 3, A, is an illustration from a current textbook
on RPDs.58 The mandibular arch has a unilateral eden-
tulous ridge that has been restored by a unilateral distal
extension RPD. The FL connects the rest on the left
mandibular first premolar with those on the right
mandibular first and second molars. The DR is situated
anteriorly to the FL; thus, the clasp on right mandibular
first molar will be put under strain each time the exten-
sion base denture is loaded, which may result in inacti-
vation of the clasp. The denture has been designed with
three minor connectors crossing the gingiva to reach
the interproximal areas and one I-bar clasp with a gingi-
val approach that may have a negative effect on oral hy-
giene, gingival health, and patient comfort.
In Figure 3, B, the design has been modified. Thus,
the DR has been placed posteriorly to the FL as the right
Fig. 4. Framework design (black) shows fulcrum line (FL) and
mandibular second molar has been used as the abut-
diagonals or retention (DR). Hatched gray surface shows sup-
ment instead of the right mandibular first molar. Thus, port available for support of RPD. A, Kennedy-Applegate class
activation of the clasp should not take place when the II according to Renner et al.59 Complex design with clasps
extension denture base is loaded occlusally. There is only and minor connectors crossing gingival margin. FL placed
one minor connector crossing the gingiva at an inter- posteriorly to anterior DR. B, Modified design shows proxi-
proximal portion as the occlusal rest on left mandibular mal minor connectors and retentive clasp arms that approach
first premolar and the indirect retainer on the left man- undercut from occlusal surface of tooth. FL and DR are close
dibular canine join the minor connector placed distally to each other.
to left mandibular first premolar. Furthermore, the in-
direct retainer mesially on the right mandibular first The design illustrated in Figure 4, B, has been simpli-
molar does not have an individual minor connector but fied. There are only two retentive elements, on the left
joins the minor connector from the clasp on the right mandibular second molar and the right mandibular sec-
mandibular second molar. Indirect retention is largely ond premolar, respectively; the three minor connectors
sufficient with this design. are all placed proximally, and there are no individual
minor connectors, running interproximally, between the
Example 4
indirect retainers on left mandibular second premolar
Figure 4, A, represents a rather complex denture design and right mandibular first premolar and the major con-
that comprises a tooth-supported base replacing left man- nector. Instead the indirect retainers in the form of rests
dibular first molar and an extension base replacing right are fastened to the denture base without crossing the
mandibular first and second molars according to Renner gingiva. The DR is almost identical to the FL and the
et al.59 The denture is designed with three clasps and two clasp design has been modified so the clasps approach
indirect retainers crossing the gingival margin. Further- the undercut from the occlusal, rather than the gingival,
more, the DR connecting the clasps of left and right man- direction. Thus, the design is simplified and more favor-
dibular second premolars is placed anteriorly to the FL. able for oral hygiene and patient comfort.

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Fig. 5. Framework design for maxillary RPD shows fulcrum Fig. 6. Maxillary framework design (black) shows fulcrum line
line (FL), diagonals of retention (DR, DR1, DR2) and support (FL), diagonals of retention (DR, DR1, DR2) and support avail-
available for RPD, hatched gray surface. A, Complex frame- able for RPD in hatched gray surface. A, Extremely complex
work design according to Davenport et al.58 with placement framework design for replacement of three teeth (left maxil-
of two DR anterior to FL. Right maxillary canine has been lary lateral incisor, canine, and first premolar) with dual-path
replaced on extension of major connector. B, Right maxillary of insertion RPD according to Shifman and Ben-Ur.51 Denture
canine replaced by denture tooth on tooth-supported den- base is mucosa/tooth-supported with FL placed anteriorly to
ture base. Rest added to maxillary right lateral incisor. All mi- DR. B, We recommend that cingulum rest placed in left max-
nor connectors placed proximally and DR and FL are close to illary central incisor to make tooth-supported base. Clasps on
each other. right and left maxillary second premolars will provide direct
retention and distal rests on right and left maxillary first mo-
lars indirect retention.
Example 5
Figure 5, A, represents a maxillary arch design for denture base replacing right maxillary canine has become
two edentulous spaces on the right side and a distal ex- entirely tooth-supported by the mesial occlusal rest on
tension ridge on the left side.58 No rest has been placed the right maxillary first premolar and the cingulum rest
on the right maxillary lateral incisor; thus, the right on right maxillary lateral incisor. The occlusal rest on left
maxillary canine has been replaced by an extension of maxillary first premolar has been placed mesially to se-
the denture base. With three retentive clasps (maxillary cure overlapping of the FL and DR. The fact that the
right second molar, first premolar and left first premo- unnecessary clasp on right maxillary first premolar has
lar), there are several DRs, all of which run anterior to been removed is positive from an esthetic point of view.
the FL. However, this may be of less inconvenience for
Example 6
a maxillary partial denture, which gains considerable
support by palatal coverage. Figure 6, A, illustrates a class V RPD where a dual-
Figure 5, B, is a slightly modified design as the small path insertion has been used.51 The denture has been

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designed with a posterior guiding plane to contact the 4. Witter DJ, Cramwinckel AB, van Rossum GM, Käyser AF. Shortened dental
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sially to the left maxillary second premolar, which pre- dysfunction and oral comfort. J Oral Rehabil 1994;21:353-66.
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66 VOLUME 80 NUMBER 1