ACADEMICS AND EDUCATION

Evolution of Removable Partial

Denture Design
Curtis M. Beck, DDS, MSD, * Dauid A. Kaiser, DDS, MSD,f
and Marvin 13.Goldfqgel,DDSS

This is a brief overview of the progress of design philosophies of removable partial dentures. It
begins in 1711 with the first published description of a removable partial denture prosthesis and
continues, with discussion of the most significant discoveries, through 1990.
J Prosthod 1994;3: 158-166. Copyright 0 1994 by the American College of Prosthodontists.

INDEX WORDS: removable partial denture, wrought wire clasp, I-bar clasp, rest-proximal
plate4 bar design, rest-proximal plate-Akers clasp design, altered cast, rotational path, swinglock

ODAYS COSCEPTS of removable partial maxillary KPL) using a palatal connector was by
T dcnturc (RPD) design are deeply rooted in the
teachings and research of the past. Some of these
KalkweI1" in 1880. Ketentive clasps were first dis-
cussed by Mouton" in 17%. In 1817, Uelabarre"
teachings are based on the empirical observations referred to "hooks" (clasps) and the use of "little
and philosophical biases of the clinician p~esenting spurs" (occlusal rests) to prevent irritation around
the concepts. Other concepts are based on attempts the abutment teeth. In 1810, C;ardette6 described the
LO integrate scientific research into the philosophical use of the wrought band clasp (Fig 3). In 1899,
and biological biases that M er e acquired during 1~onwilPrecorded his techniques for clasping abut-
professional practice. This paper rekiews the path- ments with individually contoured gold circumferen-
ways that have evolved into the modern schools of tial clasps that were then soldered to "the plate"
thought regarding RPD design (Fig 1). (major connector). Uonwill also advocated the use of
"lugs" (rest seats) so that the prosthesis would be
Early Concepts-Before 1950 supported by Ihe abutments (Fig 4). In 1913, Roach8
presented a wrought wire circumferential c l a ~ pas an
The early concepts of RPD design wcrc primarily improvement over the wide wrought band clasp. The
developed by dentists who recorded the tecliriiques first mention ofa bar clasp or "infra bulge" clasp was
that were successful in their practices. The first byIIenrichsen9 in 1914,,but the bar clasp did not gain
recorded description of an KPI) was by Heister' in popularity until Roach"' promoted this concept in
171 1 when he reported carving a block of bone to fit 1930.
the mouth. Fauchard,' who is considered by many to 'I'hc concept of rotational factors, which the early
be the father of rnodern dentistry, described the writers called "balance," was first described by Balk-
construction ofa lower KPD in 1728 using two carved well" in 1880. Prothero" is credited with coining the
blocks of ivory joined together by metal labial and term "fulcrum line." The first commercially avail-
lingual connectors (Fig 2). The first mention of a able instrument developed specifically for use in
suiveying models of tccth was designed by Weinstein
and Koth in 1921.12 During the 1930s and 1940s,
there were several articles suggesting the need for
analytical surveying of the master cast for the pur-
pose of planning the mechanics of the FU'D.''-l6 At
this same time, several articles analyzed the theoreti-
cal forces placed on clasped abutment teeth arid the
probable causes for failures with RPD."-''
During the 1930s and 19Ws, there was persistent
disagreement as to how to approach the two dissimi-
lar tissues encountered with the distal extension
WD-teeth and the mucosa covering the residual

158 Jounial ofProcthadontzcs, Val 3,,Vo 3 &pembuJ, 199J.pp 1'3-166

 S e p m h r 1994, Volume 3. Number 3 159

Heister 1711
1700 Fauchard 1728
Birth of RPD Mouton 1747

DeLabar;e 1817 Gard&e 1810

Rest Seats
Formative Balkwell 1880s
Years Bonwill 1890's
Roach 1900's
Prothero 1920's

Steffel 1950's
1950
No Rest Seats Rigid Design
W.W. Clasps Rest Seats
Karies 1956
Frechette 1956
Holmes 1965
Cecconi 1972
Investigative Kroll973
Years Koivumaa Modern RPD Design
carisson
Rigid Majw Connector
Multiple Rest Seats Periodontal Influence
Mesial Rest with I-Bar or WW Clasp

-
Prepared Guide Planes Socransky
RPD = Perio. Destruction
RPD CD

Derry
Unconventional Designs

+
1970 Bergman
Schwalm

/ J
Swinglock
I
RotationalPath
Research Simmons King
Years Positive Periodontal
Sprigg Jacobson
Results

+
Mender I
Becker
1990

Figure 1. Diagrammatic representationof the evolution of RPD design from 1700 to present.

ridge. The discussion centered around how to equal- theories and techniques based primarily on empirical
ize forces placed on the hard, relatively immovable, observation, without the benefit of scientific investiga-
abutment teeth and the soft, relatively movable, tion. Many ofthese earlyconcepts are still used in the
edentulous tissue areas. According to Stcffcl,2" the current approach to RPD design.
prominent clinicians of the time could be placed into
the following three groups: (1) those advocating
some sort of stress-breakers between the abutnirnts
Investigative Years-1950 to 1970
and the major connector; (2) those advocating broad In the 1950s, some in vivo studies were performed.
stress distribution to multiple abutments and the First, there were several cross-sectional population
edentulous area; and (3) those advocating physiologi- studies performed in England that showed extensive
cal or functional basing. pathological changes in the periodoritium of patients
Steffel placed himself into the broad stress distri- who wore R P D S . ~Next,
~ - ~ there
~ appeared a series of
bution group but conceded that all three methods longitudinal studies performed in Scandinavia, pri-
could be successful if properly executed. He rejected marily by KoiLumaa and Carlsson,Y4-LH that also
the common practice of constructing a distal exten- showed extensive pathological changes in the peri-
sion RPDs from a single impression. odontium and increased caries activity for patients
Before 1950, RPD concepts wcrc mostly devel- who Wore RPDs. One clinical study performed in
oped by a small group of authors who presented their Switzerland showed increased mobility of abutments
160 Eoolution ofRPD Design Beth, Kairer. and Gnldfogd

Figure 4. Drawing of an RF’D using rests and circumfer-

ential clasps as advocated by Bonwell, circa 1899.

periodontal therapy had not yet been shown. Even

the correlation between plaque and periodontal dis-
ease could not be proven until Loe et al’s classic study
was published in 1965.30It should also be pointed out
that in the 1950s, the partial denture concepts in
Europe were vastly different from the accepted
Figure 2. Drawing of an early RPD, circa 1728. concepts in North America. In Europe, the RPDs
tended to provide a flimsy design with wrought wire
when RPDs were worn by the subjects.2q These clasping and, usually, no rest seats. In North America,
studies represent the first scientific attempt by re- the partial denture design tended to include rigid
searchers to evaluate the theories of the previous major connectors, cast clasps, and rest scats.
decades on actual patients. There was no effort to During the 1950s, the first attempts to evaluate
evaluate RPD design, to evaluate the effect of oral RPD design theories through in vitro studies ap-
hygiene, to institute basic periodontal care before peared primarily the analog study. In 1956, h i r e s 3 ’
placement of the removable prosthesis, and to pro- showed that the lingual bar of a lower RPD should be
vide recall maintenance for any of the patients rigid to distribute forces across the arch. Also, an
evaluated. The results were predictably condemning increase in residual ridge coverage reduced forces to
for RPD prostheses. These studies gave credence to abutment teeth. In 1956, Frechette3‘ showed that
the then prevailing attitude of the profession, as well multiple occlusal rests helped to distribute forces to
as of the public, that RPDs were detrimental to the more abutments and, thus, reduced forces to the
existing dentition and were considered an interim terminal abutments.
appliance on the pathway to complete dentures. In the 1960s, two important studies were per-
However, in defense of these studies, it should be formed in connection with the problem of two dissimi-
pointed out that many of today’s routine advances in lar tissues (resilient and nonresilient) when construct-
ing distal extension RPDs. Holmesj3 and L e u ~ o l d ~ ~
both showed that distal extension partial dmtures
constructed on one-piece casts exhibit more move-
ment of bases than those constructed using an
altered cast procedure. The original altered cast
technique was first presented to the profession by
A ~ p l e g a t e . ~His
” . ~technique
~ was somewhat cumber-
some and used wax that flowed under function at
mouth temperature to register the tissue form of the
edentulous distal residual ridge for the lower RPD.
The original technique has been greatly simplified
with the advent of modern elastomeric impression
r n a t e r i a l ~ .Advantages
~~,~~ of the altered cast proce-
dure have more recently been confirmed by Vahidi39
and by Leupold et a P
During the 1960s and early 1970s, two influential
Figure 3. Drawing of an RPD using the broad wrought clinicians increased the popularity of the bar clasp
band clasp made popular by Gardette and Bonwill in the concept started by Henrichsen and Roach many
early 1800s. years before. Kr-atochvi14’promoted the use of the
 September 19.94, Volume 3, N u m b d 161

Figure 7. Diagram of RPA4clasp suggested by Eliason

Figure 5. Diagram of I-bar clasp suggested by Kratoch-

vil. Research in Earnest-
1970 to Present
During the 197Os, there began to appear a large
I-bar clasp with a mesial occlusal rest as a means of
number of studies beginning with in vitro research.
reducing the force on a clasped abutment when
Cecconi et a146showed that force to the abutment
dealing with distal extension RPDs (Fig 5). Kr01‘*
teeth was transmittcdvia the rest seats, and that this
modified Kratochvil’s concept with his mesial rest-
force was the same with or without retentive clasps.
proximal platc-I bar (RPI) design (Fig 6). These two
Robinson4’ showed that forces to abutment teeth
clinicians were a major influence in thc eventual, with distal extension RPDs are minimized with a
nearly universal, acceptance of the I-bar concept in mesial rest (as opposed to a distal rest) and that a
North America. Despite the acceptance of the theo- wrought wire retentive clasp has the same force on
retical advantages to the I-bar concept, it became the abutment as an I-bar design when used with a
increasingly apparent that there were contraindica- mesial rest. He also demonstrated that no clasp is
tions to the exclusive employment of the I-bar passive, as had been deemed essential by nearly all
retention design. Some of the problems encountered theoretical concepts proposed in the past. Nally*8
included insufficient vestibular depth, soft tissue showed that a mesial rest created the least amount of
undercut below the abutment tooth, and lack of abutment movement and that abutment movement
“I-bar usable” undercuts. increased with the removal of indirect retainers.
As a result of these limitations for the I-bar Browning et a149confirmed the value of the mesial
system, there evolved a modification that combined rest with either the I-bar or the wrought wire clasp
the I-bar and circumferential clasp designs. This design. Frank and N i c h o l l ~showed
~~ that indirect
clasp design is called the mesial rest-proximal platc- retainers have little to do with retention of a distal
Akers clasp (RPA) and was developed by KroP3 and cxtcnsion RPD; rather, it is the guide planes that
E l i a ~ o n The
. ~ ~ mesial rest and proximal plate are create retention in conjunction with clasping. They
identical to the RPI system, but the buccal retentive showed that indirect retainers do help with force
distribution and, thus, are a beneficial component in
arm becomes a circumferential or Akers clasp engag-
RPD design. An earlier study by Fisher and Jaslows’
ing a mesial undercut. The superior border of the
supports the findings of Frank and Nicholls.
rigd portion of the Akers clasp should contact the
Photoclastic studies provided a new laboratory
tooth on the survey line (Fig 7). Nelson et a145
research tool for evaluating RPD design. Kratochvil
suggested using a cast round clasp rather than the and Caputo5* showed that an KPD framework that
conventional half round design to form the retentive had been properly adjusted to fit the abutments
Akers clasp. created less force to the abutments than a frame-
work that had not been adjusted. Thompson et a153
reported the most favorable force to abutments
came with a mesial rest and either a wrought wire or
an I-bar retentive clasp. Pezzoli et aI5*confirmed the
value of mesial rests, indirect retainers, and multiple
rest seats on force distribution.
Attempting to correlate an in vitro study directly
to a clinical situation is difficult and may be mislead-
ing. One study by Clayton and Jaslodj illustrates
Figure 6. Diagram of RPl clasp suggested by Krol. this problem. Most analogue studies measure the
162 Euolutwn +RPD Design Becker, KazSu, and Goldjogel

movement of the abutment teeth when certain lesions associated with the prosthesis. They per-
forces are placed on the RPD. However. Clayton and formed preperiodontal therapy, provided oral hy-
Jaslow measured the movement of the clasps on the giene instruction, used accepted RPD design prin-
corresponding abutmcnts. Browning et aP9 showed ciples, and established a recall program for the
that the clasp moves more than the corresponding subjects being investigated. In 1977, Schwalm et a159
abutment. The major reasoris for using wrought wire reported the results of a 2-year investigation in which
clasps are that the wire is more flexible than a cast acceptable RPD design principles were used and
clasp and that wire can flex in three dimensioris. The initial plaque control instructions and basic periodon-
fallacy in Clayton and Jaslou's study is that move- tal therapywere instituted, but there was no periodic
ment of the clasp docs not necessarily translate into recall. They found no increase in mob
movement of the abutment, and, thus, comparisons decrease in sulcular depth to partial prosthesis abut-
of the force placed on the corresponding abutment ments. Chandler and BrudvikG0 reported that in an 8-
by measuring the movement of the clasp is invalid. to 9-year study, they found some gingival inflamma-
This study has been widely misquoted as justification tion but no periodontal breakdown associated with
for using an I-bar instead of the more flexible RPDs. Bergman and EricsonG1reported that in a
wrought wire clasp. Clayton and Jaslow's study does 3-year cross-sectional study, thcy found no adverse
confirm that there is no such thing as a passive
periodontal results associated with the wearing of
cla~p.~~~"'
RF'Ds. Also, those patients that maintained a regular
From the increased interest in scientifically evalu-
recall schedule did better than those who did not.
ating the design concepts of the past, there began to
In 1979, Tebrock et a P reported a clinical study in
emerge the following sound basic principles for RPD
which they attempted to correlate different clasp
design:
designs with abutment mobility. They discovered
1. Major connectors should be rigid. that thcre was no measurablc mobility, regardless of
2. Multiple rest seats appear to distribute forces the clasp design, when the altered cast procedure
favorably. had been used. In 1979, Maxfield et alG3attempted to
3. Mesial rests appear to provide some advantage measure abutment mobility in the mouth with differ-
whcn used with distal extension RPDs. ent clasp designs and different rest placcmcnts. They
4. Parallel guide planes are beneficial for retention reported no measurable mobility, regardless of rest
and stability of a prosthesis. position and clasp design, when the altered cast
5.The I-bar or the wrought wire retentive clasp, in procedure had been used.
combination with a mesial rest, may be a superior A possible criticism of some of the clinical investi-
design for the distal extension RPI). gations was that the study did riot involve a large
6. The altered cast procedure reducrs moverncnt of enough sample group. In an attempt to counter this
the distal extension RPL), at least initially. criticism, Kratochd et alb4correlated three sample
Clinical research began to gain momentum as groups in the Netherlands, England, and the United
periodontal awareness increased. More valid and States over a 1- to 5-year period. No attempts were
reliable concepts for RPL) design evolved that relied made for preprosthetic periodontal therapy, oral
less on empirical observation. These studics were hygiene, or periodic recall. No standardization of
performed by researchers taking a critical look at the RPD design was established. They reported in-
earlier attempts to evaluate the effects of RPDs on creased mobility, increased bone loss to all teeth
the remaining dentition. In 1966, Rudd and O'J,ear)PS6 (abutments, as well as those not contacted by the
did a brief longitudinal study in which they reported prosthesis), and plaque retention of 62% of all tooth
that, when proper guide planes were established on surfaces. In other words, they rcported the same type
periodontally treated patients, mobility to abutment of deleterious results as the researchers of the 1950s
teeth remained the same or improved. In 1970, and 1960s had reported whcn basic periodontal
Derry and Ulrik5' reported in a 2-year study, that no considerations and minimal RPD design concepts
change was demonstrated in mobility, gingival index, were not applied.
or plaque index. Their study incorporated minimal When we compare thc longitudinal studies per-
RF'D design standards. Bergman et alj*reportcd that formed during the 1950s and 1960s with those
in a 2-year study, they found no increase in mobility, performed since 1970, it becomes clear that the
no change in gingival index, and very few carious results are nearly opposite. Before 1970, the studies
 Septeniber 1994. Volume .3,lVumber3 163

tended to show that KPl)s were detrimental to oral these relatively new and radical design concepts are
health. This prompted some clinicians to warn against the swinglock design and the rotational path design.
using WDs, and some clinicians even suggasted that The swinglock design was first introduced to the
partial dentures may cause more harm than good.65 dental profession by Simmonsw' in 1963. Simmons
Since 1970, we have seen many studies that suggest took advantage of the casting properties of the
that H l ) s can help provide positive oral hralth if chrome cobalt metals to devise a hinge and lock
proper attention is given to: (1) oral hygiene; (2) system that allowed for a retentive labial bar that can
preprostlietic periodontal therapy; (3) minimal stan- he opcncd and closed by the patient. This radical
dards for RPI) design; and (4) pariodic racall to technology allo~v~sfor successful use of periodontally
evaluate the status of thc pcriodontium and the compromised abutment teeth, as well as situations in
continued function of the prosthesis. which critical abutments are missing (Fig 8A through
C ) . Bolender and Beckerb7have suggested certain
specific indications for the swinglock design includ-
Unconventional Designs ing: periodontal compromised abutments, missing
With increased kriow4edge in the various dental key abutments, abutment mobility, limited econom-
discipline.,, particiilarly periodontic., and endodon- ics, and maxillofacial prosthesis. Specificdesign crite-
tics, came the ability to extend the useful life of ria have been suggested by Becker and BolenderfiH
previously questionable abutment teeth. This has led arid by Becker and S ~ o o p e . No
" ~ analogue or photo-
to some innovative KPD concepts that prewously elastic studies have been performed to test these
may have been unacceptable. The most notable of design concepts, and they have not met with univer-

Figure 8. (-4)Patient with extensive peritxlorital involvcment of the lower anterior teeth requiringc:xtraction oftceth no.
23 through 26, pcriodontal treatment and stabilization of the remaining teeth. (B) After extractions and sur~:essful
periodontal therapy to the remaining abutment t rrt h. Note extensive free gingival graft t o labial \.rstihrlle. ((2) The
remaining abutment teeth arc stabilized using the swinglock KPD design. (U) Radiographs spanning 16 years.
164 Eoolution OfRPD Design Beckq Kaiser, and Gol#ogel

sal acceptance. Antos, Renner, and Foerth’O prefer design was limited to tooth-borne situations in which
no rest seats and place the hinge and clasp o f the anterior teeth were missing. Other investigators
labial retentive arm next to the terminal abutments. have expanded and clarified the design principles to
Becker, Bolender, and S ~ o o p erecommend
~ ~ ? ~ ~ the include edcntulous spaces in any part o f the a r ~ h . ~ ~ - * O
use of multiple rest seats and suggest placing the The swinglock and dual path concepts are good
hinge and clasp o f the labial retentive bar at least one examples of design modifications that have evolved
tooth distal to the terminal abutments. because of a need to solve special problems.
There have been very few clinical studies per-
formed to evaluate the swinglock design. Sprigg”
reported a favorable 6-year clinical evaluation of
Summary
patients in which the swinglock design was used. This is a review of the evolution of RPD design
Gomes et reported that in a pilot study over a concepts, beginning with the first recorded mention
2-year period using swinglock RPDs, they found no of an RPD in 1711 and continuing with the most
periodontal changes. Gomes et aP3 also reported significant theories through 1990. The long-term
favorable results with a 3-year study using the swing- success of an RPD prosthesis can be favorable,
lock design. provided proper attention is given to oral hygiene,
The dual path (or rotational path) RPD concept is periodontal considerations, basic RPD design con-
relatively new, having been introduced by I Z I ~ ~ ’ ~ Jcepts,
~ and judicious execution of partial denture
and in 1978. Initially, the dual path design construction,
arose out of the need for an RPD that would be
estheticwhen anterior pontics are present; primarily,
the desire to eliminate anterior clasping. This tech- References
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 Sepember 1994. Volume3, Number3 165
~

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