406 > REVIEW

www.sada.co.za / SADJ Vol. 78 No.8

A simplified and evidence-informed

approach to designing removable
partial dentures
Part 1: Evidence-informed design principles
SADJ September 2023, Vol. 78 No.8 p406-409
Prof CP Owen1

SUMMARY INTRODUCTION TO PART 1

For many decades the literature has regularly reported that As stated in the summary, many papers have reported on
there is a discrepancy between what is taught in dental the lack of information prescribed by dentists to the dental
school and what is practised, especially in the field of technician. Rather than setting these out in narrative form,
removable partial dentures. Not only that, but for more than studies from the last 45 years are summarised in Table 1.
60 years reports from around the world have shown that, The inevitable conclusion from these studies is that little has
usually, the majority of clinicians abdicate their responsibility changed over the last many decades, where there still seems
to design a removable partial denture (RPD) and instead to be an enormous amount of what can only be described
leave this to the dental technician, who has no knowledge as malpractice when clinicians abdicate their responsibility
of the clinical condition of the patient and works only from a for the design of removable partial dentures. This is the
cast. Most patients around the world who require RPDs to motivation for this series of papers, to try to simplify both
improve aesthetics and chewing can only afford a removable the understanding and the application of design principles.
prosthesis simply because the majority are poor. But RPDs
can improve these aspects and contribute to an improved THE DESIGN PRINCIPLES
quality of life. An article that discussed key turning points in RPD
philosophy revealed that RPDs have been described in the
The purpose of this series of articles is to derive the basic, literature for just over 300 years.18 However, there seems to
evidence-informed principles of partial denture design have been few changes over the last nearly 100 years. While
and to suggest a simplified explanation and application of there are no universally accepted principles for the design
those principles in the hope that clinicians will increasingly of RPDs, these can in fact be derived from evidence in the
take responsibility for the design of partial dentures. Part 1 literature.
summarises studies revealing what can only be described
as the malpractice of abdication of responsibility for design Tooth support
by clinicians, and then explain the evidence-informed basic Early attempts to provide retention were described in the
principles of design; Part 2 will look at the biomechanical early 19th century as metal bands encircling the teeth. These
basis of those principles in terms of support; Part 3 will do often extended into the gingival sulcus with somewhat
the same for the biomechanical basis of retention; Part 4 will disastrous effects on the periodontium. A fortuitous effect
provide a simple seven-step approach to design, applied to of this was the realisation that tooth support was required,
an example of an acrylic resin-based and a metal framework- and the first occlusal rest was described in 1817.19 This
based denture for the same partially edentulous arch; and prevented components such as the bands sinking into the
Part 5 will provide examples of designs for RPDs that have gingiva and mucosa and should have become a universally
been successfully worn by patients, for each of the Kennedy accepted principle. Sadly, there is much evidence that RPDs
Classifications of partially dentate arches. Much of this is are still being made, more than 200 years later, with no
referenced from an electronic book on the Fundamental of tooth support (see Table 1), most notably as acrylic resin-
removable partial dentures.1 based dentures or, more recently, as the so-called flexible
denture.16,20,21
Keywords
Removable partial denture, design, support, retention, In a study comparing dentures with and without tooth
acrylic-based, framework-based support, it was found that patients who had adequate and
sufficient rest seats were more satisfied with their dentures
Author’s information than those whose dentures had inadequate support.22
1. CP Owen, Professor Emeritus, Faculty of Health Sciences, University Adequate support was one of the few criteria that correlated
of the Witwatersrand, Johannesburg, South Africa with successful wearing of mandibular Kennedy Class I
Corresponding author
RPDs.23
Name: Prof CP Owen
Tel: +27 83 679 2205 Clasps
Email: peter.owen@wits.ac.za A century after the concept of a clasp as a band, Roach
Conflict of interest pioneered the use of wrought wire as a circumferential
None clasp and as an “infra-bulge” clasp.24 Clasps provide
 REVIEW < 407
www.sada.co.za / SADJ Vol. 78 No.8

Table 1. A selection of studies from the last 45 years on information supplied by clinicians to dental laboratories for removable partial dentures.
Year Country Study Results Reference
1978 England and 124 metal-based 54% had no instructions 2
Wales, UK dentures and 44
maxillary acrylic-
based dentures
1978 UK 14 laboratories, 36% had a written prescription of the design; 4.6% of the casts 3
1,858 partial showed any evidence of tooth preparations such as for rest seats
dentures
1984 USA 303 laboratories 78% of the technicians designed most or all of the dentures; 76% of 4
the master casts did not show adequate tooth preparation
1993 South Africa 148 dentists 82% of dentists instructed the technician to design the RPD; 64% did 5
not survey the casts; 55% were not mounted on an articulator
1986 Scotland, UK 539 casts and 34% were acrylic-based, 6% of which had clasps, but none had 6
dentures in one occlusal rests; 3.4% gave detailed instructions for acrylic-based
laboratory dentures and 21.3% for metal-based dentures
2003 Ireland 122 sets of 53% lacked any design instruction; 9% of those requested the 7
instructions to dental technician to design the framework; 7% of all the instructions included
laboratories a diagram
2005 UK 8 laboratories, 134 40% included a diagram for a metal-based denture; 9% included 8
prescriptions surveyed study casts; 28% requested the dental technician to design
the case
2006 Tanzania 328 prescriptions to 2.4% indicated a design for acrylic-based RPDs; 13.4% requested 9
a hospital laboratory clasps; no other design parameters were requested
2007 Bahrain 131 prescriptions to 76% requested the dental technician to design the denture, 79% for 10
5 laboratories acrylic-based dentures and 57% for the metal-based dentures; 18%
mentioned any design variables
2011 Wales, UK 68 master casts 48% did not have prescriptions or designs including rest seats; 11
from impressions of those that did, only 30% had an obvious and visible rest seat
taken by 45 dentists preparation on the cast
using predetermined
criteria for cingulum
and occlusal rest
seat preparations
2014 China 5 commercial 90% of the written instructions showed the type and position of 12
laboratories in major clasps; 88% gave information regarding connectors; 48% of the tooth
cities across China preparations were inadequate: there were no proper guide planes, rest
seats or contours to accommodate components; 33% of technicians
would contact the dentist for clarification when they felt it was needed
2018 Turkey 25 laboratories 38% of clinicians provided any instructions to the dental technician: 13
58% of prosthodontists, 33% of dentists. For those who did provide
instructions, (47%) a diagram was the preferred choice
2020 Saudi Arabia 9 commercial 64.2% had no design instructions; 6% provided a diagram; 10% drew 14
laboratories, 162 a design on the cast
prescriptions and
casts
2020 South Africa 60 cases from 55% had no rests overall; 65% of the acrylic-based dentures had no 15
3 commercial rests; 85% had no clasps, and none of the “flexible” dentures had
laboratories rests or clasps
2022 South Africa 3 commercial 0% prescribed the design; 119 clasps were made, but only one 16
laboratories, 114 cast was surveyed; 92% of the acrylic-based dentures had no tooth
cases support; 11 (14%) of the 81 rests (in 25 of the dentures) were pre-
prepared on the teeth
2023 China 916 prescriptions to a 86.8% had inadequate design diagram information; 74.2% were
17
laboratory assessed as failing to meet an acceptable clinical quality standard

retention by the force exerted against the tooth as they flex health than circumferential clasps26 so their use will not be
while emerging from the undercut below the bulge of the advocated here.
tooth. However, the amount of this force and the ability of
all clasp materials to bend many times without distortion Guide planes and guiding surfaces
has not been fully elucidated. A recent paper has provided A guide plane is the prepared surface of a tooth adjacent to
some guidelines for cast clasps and stainless steel round to an edentulous space, and a guiding surface is that part of
wire25 but there are still other casting alloys and pre-formed the denture which contacts the guide plane. Close contact
wrought wire clasps that need to be tested. Pre-formed of these provides for frictional resistance when the denture
and cast gingivally-approaching clasps were shown almost moves. It is important to realise that this resistance is least
40 years ago to be potentially more damaging to gingival along the path of insertion, and greatest if the denture is
408 > REVIEW www.sada.co.za / SADJ Vol. 78 No.8

removed along any other path, rather like a drawer in a desk. improving chewing ability may be vital for a number of
This is a much underestimated contributor to retention, and reasons. The link between chewing ability and food choices
when the remaining teeth are sufficiently distributed can has been established through several national surveys of
provide all the retention needed without the use of clasps.27 large numbers relating loss of all or some teeth to adverse
food choices.41 Such (wrong) food choices place patients
These three basic design principles govern the features that at risk of increasing morbidity, and so it would seem logical
should be considered for all RPDs. There are, of course, that improving masticatory ability by replacing missing teeth
other factors that contribute to the successful use of RPDs. would also remove those risks of morbidity. Unfortunately,
These include minimal gingival coverage wherever possible, this is not necessarily the case, and merely improving
and the elimination of redundant components without mastication by providing prostheses does not guarantee an
compromising biomechanical requirements.28,29 improvement in food choices and therefore overall nutrition.42
The answer, therefore, is not to make such assumptions,
THE BIOLOGICAL PRICE OF RPDS but to provide, whenever placing a prosthesis for a patient,
For too long, the observation of increased tooth loss nutrition analysis and counselling. Unfortunately, this appears
following the wearing of RPDs was attributed to the forces to be as rare among practitioners as is the designing of
placed on the abutment teeth, as the teeth usually carrying RPDs.
the clasps. This wasn’t helped by the theoretical studies of
Kratochvil as far back as 1963 in which he surmised that A somewhat still controversial additional reason for improving
a distal extension base produced a tipping force on the chewing ability is the link between the ability to chew and
abutment tooth, and advocated an RPI clasp (mesial rest, cognition, and especially cognitive decline and dementia.
proximal plate and I-bar) to offset this.30 This was based on Interest in this aspect has increased in the last two decades,
the difference between compression of the mucosa under with the use of such instruments as functional magnetic
the distal extension and the compression of the periodontal resonance imaging and electrical brain activity recordings. A
ligament of the abutment tooth. It seemed logical and was large body of literature now exists on this and it is generally
followed by purely laboratory studies using photoelastic resin accepted there is indeed an association between loss of
to “prove” the effects that the RPI design was supposed teeth and masticatory ability and dementia. The question is,
to overcome.31 These are mentioned here because some is this just an aspect of dementia in that dementia is a part
believe it to this day, but there have never been any clinical or maybe a cause of loss of teeth (among other things), or
studies to show this is indeed the case and it was refuted, is it the loss of teeth and difficulty with chewing that causes
also many years ago. 32 cognitive decline and dementia? The case for the latter
is increasingly being made,43,44 which has the potential to
So, while it seemed logical that a partial denture gripping make the replacement of teeth, especially in the elderly, a
an abutment tooth would exert a tipping and torquing force public health measure.
on that tooth, this has never been shown clinically. What
has been shown clinically is that abutment teeth are indeed Flying somewhat in the face of these arguments is the
more likely to be lost,3 but the reasons are multifactorial, not concept of the Shortened Dental Arch. Once again there is
least of which is the influence of plaque. This is the severest a large body of literature on this concept, first proposed in
biological price because a prosthesis provides many more 1981, that for a dentition with loss of posterior teeth, bilateral
surfaces for plaque to accumulate on, and this changes the contact on the premolars was sufficient.45 There have been
ecology of the mouth, resulting in gingival and periodontal many papers testing this and, recently, some reviews of the
disease, root caries and stomatitis, especially in dentures clinical studies and while the concept remains somewhat
without tooth support.34-38 controversial, it is generally considered to be valid, with
the proviso that methodological problems with the clinical
The common conclusion of all studies is that intensive and studies made it difficult to advocate for all cases.46,47 This
meticulous oral hygiene should be a prerequisite for the is a fair conclusion for many aspects of prosthodontics and
insertion of RPDs. means that treatment must always be patient-centred. The
main problem is that the lack of posterior teeth can affect
DO THEY REALLY WORK? food choices adversely, so perhaps a nutrition analysis
This seems at first a strange question to ask, when so should always be the first step.
many RPDs are made all over the world. But it must be
asked, because many papers have reported fairly high There is no doubt that if a prosthesis can be omitted then it
levels of dissatisfaction expressed by patients,39 with one should be.
retrospective study finding that 39% of the dentures were
no longer used after 5 years.40 The adage that all dentures SUMMARY
are easy to wear but not all are easy to use certainly applies It is essential that all dentists and dental technicians have a
to RPDs. The conclusion above has implications not only clear understanding of the evidence-informed principles of
for the need to change patient behaviour but also, and all aspects of RPD design, and especially of the biological
importantly, for the design of the denture so that it can price exacted by these dentures. Meticulous preparation of
actually be used – and used successfully. the mouth prior to treatment is required, so that dentures
are placed in a plaque-free environment, and that the patient
ARE THEY REALLY NEEDED? must be committed to thorough oral hygiene practice and
This is not a strange question because, as will be shown regular recalls.
in Part 4, the first step in designing an RPD is to establish
the need. Not all missing teeth need to be replaced. The The next part will deal with the biomechanical basis of
most common requested needs are to improve aesthetics support.
and chewing ability. Aesthetics is an obvious one, but
www.sada.co.za / SADJ Vol. 78 No.8
REVIEW < 409

REFERENCES 25. Owen CP, Naidoo N. Guidelines for the choice of circumferential wrought wire and
cast clasp arms for removable partial dentures. Int Dent J. 2022;72(1):58-66. doi:
1.  Owen CP. Fundamental of removable partial dentures. 5th Ed. Electronic book,
10.1016/j.identj.2021.01.005
available at https://www.appropriatech.com/ Accessed 5 September 2023
26. Bazirgan MK, Bates JF. Effect of clasp design on gingival health. J Oral Rehabil.
2. Basker RM, Davenport JC. A survey of partial denture design in general dental
1987;14(3):271-81. doi: 10.1111/j.1365-2842.1987.tb00719.x
practice. J Oral Rehabil. 1978;5(3):215-22. doi: 10.1111/j.1365-2842.1978.
27. Mothopi-Peri M, Owen CP. Guide-Plane Retention in Designing Removable Partial
tb01238.x
Dentures. Int J Prosthodont. 2018;31(2):145-8. doi: 10.11607/ijp.5525
3. Schwarz WD, Barsby MJ. Design of partial dentures in dental practice. J Dent.
28. Runov J, Kroone H, Stoltze K, Maeda T, El Ghamrawy E, Brill N. Host response to
1978;6(2):166-70. doi: 10.1016/0300-5712(78)90213-0
two different designs of minor connector. J Oral Rehabil. 1980;7(2):147-53. doi:
4. Dullabh HD, Slabbert JC, Becker PJ. Partial denture prosthodontic procedures
10.1111/j.1365-2842.1980.tb00431.x
employed by practising graduates of the University of the Witwatersrand,
29. Chandler JA, Brudvik JS. Clinical evaluation of patients eight to nine years after
Johannesburg. J Dent Assoc S Afr. 1993;48(3):129-34
placement of removable partial dentures. J Prosthet Dent. 1984;51(6):736-43. doi:
5. Owall B, Junggreen L, Yemm R. Removable partial denture production in Scotland.
10.1016/0022-3913(84)90366-4
Quintessence Int. 1996;27(12):809-15
30. Kratochvil FJ. Influence of occlusal rest position and clasp design on movement of
6. Taylor TD, Matthews AC, Aquilino SA, Logan NS. Prosthodontic survey. Part I:
abutment teeth. J Prosthet Dent. 1963;13(1):114-124
Removable prosthodontic laboratory survey. J Prosthet Dent. 1984;52(4):598-601.
31. Kratochvil FJ, Caputo AA. Photoelastic analysis of pressure on teeth and bone
doi: 10.1016/0022-3913(84)90355-x
supporting removable partial dentures. J Prosthet Dent. 1974;32(1):52-61. doi:
7.  Lynch CD, Allen PF. A survey of chrome-cobalt RPD design in Ireland. Int J
10.1016/0022-3913(74)90098-5
Prosthodont. 2003;16(4):362-4
32. Berg E. Periodontal problems associated with use of distal extension removable
8. Lynch CD, Allen PF. Quality of written prescriptions and master impressions for fixed
partial dentures - a matter of construction? J Oral Rehabil. 1985;12(5):369-79. doi:
and removable prosthodontics: a comparative study. Br Dent J. 2005;198(1):17-20.
10.1111/j.1365-2842.1985.tb01542.x
doi: 10.1038/sj.bdj.4811947
33. Tada S, Ikebe K, Matsuda K, Maeda Y. Multifactorial risk assessment for survival
9.  Carneiro LC. Specifications provided by practitioners for fabrication of
of abutments of removable partial dentures based on practice-based longitudinal
removable acrylic prostheses in Tanzania. J Oral Rehabil. 2006;33(9):660-5. doi:
study. J Dent. 2013;41(12):1175-80. doi: 10.1016/j.jdent.2013.07.018
10.1111/j.1365-2842.2005.01611.x
34. Brill N, Tryde G, Stoltze K, El Ghamrawy EA. Ecologic changes in the oral cavity
10. Radhi A, Lynch CD, Hannigan A. Quality of written communication and master
caused by removable partial dentures. J Prosthet Dent. 1977;38(2):138-48. doi:
impressions for fabrication of removable partial prostheses in the Kingdom of
10.1016/0022-3913(77)90278-5
Bahrain. J Oral Rehabil. 2007;34(2):153-7. doi: 10.1111/j.1365-2842.2006.01685.x
35. do Amaral BA, Barreto AO, Gomes Seabra E, Roncalli AG, da Fonte Porto Carreiro
11. Rice JA, Lynch CD, McAndrew R, Milward PJ. Tooth preparation for rest
A, de Almeida EO. A clinical follow-up study of the periodontal conditions of
seats for cobalt-chromium removable partial dentures completed by general
RPD abutment and non-abutment teeth. J Oral Rehabil. 2010;37(7):545-52. doi:
dental practitioners. J Oral Rehabil. 2011;38(1):72-8. doi: 10.1111/j.1365-
10.1111/j.1365-2842.2010.02069.x
2842.2010.02130.x
36. Emami E, Taraf H, de Grandmont P, Gauthier G, de Koninck L, Lamarche C, de
12. Sui L, Wu X, Wu S, Gao P, Li R. The quality of written instructions for dental
Souza RF. The association of denture stomatitis and partial removable dental
prostheses in China. J Prosthodont. 2014;23(8):602-9. doi: 10.1111/jopr.12163
prostheses: a systematic review. Int J Prosthodont. 2012;25(2):113-9
13. Cebeci NÖ. Factors associated with insufficient removable partial denture design
37. Hussain KA, Azzeghaibi SN, Tarakji BRSS, Sirajuddin S, Prabhu SS. Iatrogenic Damage
instructions. Dent Med Probl. 2018;55(2):173-7. doi: 10.17219/dmp/89646
to the Periodontium Caused by Removable Prosthodontic Treatment Procedures:
14. Nassani MZ, AlOtaibi MS. Quality of communicating design features for cobalt
An Overview. Open Dent J. 2015;9:187-9. doi: 10.2174/1874210601509010187
chromium removable partial dentures in Riyadh, Saudi Arabia. Eur Oral Res.
38. Moldovan O, Rudolph H, Luthardt RG. Biological complications of removable dental
2020;54(3):123-9. doi: 10.26650/eor.20200117
prostheses in the moderately reduced dentition: a systematic literature review. Clin
15. Farao W, Geerts G. Conformity of removable partial denture designs to agreed
Oral Investig. 2018;22(7):2439-61. doi: 10.1007/s00784-018-2522-y
principles based on materials used - A preliminary study. SADJ. 2020;75:253-9
39. Frank RP, Milgrom P, Leroux BG, Hawkins NR. Treatment outcomes with mandibular
16.  Daya R, Owen CP. Conformity of removable partial denture designs from
removable partial dentures: a population-based study of patient satisfaction. J
three laboratories to a set of design principles. SADJ 2022;77(8):459-64 doi:
Prosthet Dent. 1998;80(1):36-45. doi: 10.1016/s0022-3913(98)70089-7
10.17159/2519-0105/2022/v77no8a1
40. Koyama S, Sasaki K, Yokoyama M, Sasaki T, Hanawa S. Evaluation of factors
17. Zhang N, Mao B, Dai Y, Chen S, You Z, Zhang J, Chen X, Dong H, Yue L, Yu
affecting the continuing use and patient satisfaction with Removable Partial
H. Audit to assess the quality of 916 prosthetic prescriptions of removable partial
Dentures over 5 years. J Prosthodont Res. 2010;54(2):97-101. doi: 10.1016/j.
dentures. Hua Xi Kou Qiang Yi Xue Za Zhi. (West China Journal of Stomatology)
jpor.2009.11.007
2023;41(3):315-22. English, Chinese. doi: 10.7518/hxkq.2023.2021565
41. Walls AW, Steele JG. The relationship between oral health and nutrition in older
18.  Waliszewski MP. Turning points in removable partial denture philosophy. J
people. Mech Ageing Dev. 2004;125(12):853-7. doi: 10.1016/j.mad.2004.07.011
Prosthodont. 2010;19(7):571-9. doi: 10.1111/j.1532-849X.2010.00622.x
42. Wöstmann B, Michel K, Brinkert B, Melchheier-Weskott A, Rehmann P, Balkenhol
19. Delabarre CF: Discours d’ouverture d’un cours de medicine dentaire. Paris, 1817,
M. Influence of denture improvement on the nutritional status and quality of life of
390 pp. Not read in the original: cited by Waliszewski, 2009
geriatric patients. J Dent. 2008;36(10):816-21. doi: 10.1016/j.jdent.2008.05.017
20. Horie N, Ouchi T, Nishiyama R, Usuda S, Morikawa S, Asoda S, Nakagawa T.
43. Ahmed SE, Mohan J, Kalaignan P, Kandasamy S, Raju R, Champakesan B. Influence
Vertical Displacement in Unilateral Extension Base Flexible Removable Dentures.
of Dental Prostheses on Cognitive Functioning in Elderly Population: A Systematic
Bull Tokyo Dent Coll. 2019;60(4):233-9. doi: 10.2209/tdcpublication.2018-0068
Review. J Pharm Bioallied Sci. 2021;13(Suppl 1):S788-S794. doi: 10.4103/jpbs.
21. Fueki K, Ohkubo C, Yatabe M, Arakawa I, Arita M, Ino S, et al. Clinical application of
JPBS_773_20
removable partial dentures using thermoplastic resin-part I: definition and indication
44. Kim MS, Han DH. Does reduced chewing ability efficiency influence cognitive
of non-metal clasp dentures. J Prosthodont Res. 2014;58(1):3-10. doi: 10.1016/j.
function? Results of a 10-year national cohort study. Medicine (Baltimore).
jpor.2013.12.002
2022;101(25):e29270. doi: 10.1097/MD.0000000000029270
22. Koyama S, Sasaki K, Yokoyama M, Sasaki T, Hanawa S. Evaluation of factors
45. Käyser AF. Shortened dental arches and oral function. J Oral Rehabil. 1981;8(5):457-
affecting the continuing use and patient satisfaction with removable partial dentures
62. doi: 10.1111/j.1365-2842.1981.tb00519.x
over 5 years. J Prosthodont Res. 2010;54:97-101
46. Khan SB, Chikte UM, Omar R. An Overview of Systematic Reviews Related to
23. Frank RP, Brudvik JS, Leroux B, Milgrom P, Hawkins N. Relationship between the
Aspects of the Shortened Dental Arch and Its Variants in Adults. Int J Prosthodont.
standards of removable partial denture construction, clinical acceptability, and
2017;30(4):357-66. doi: 10.11607/ijp.5287
patient satisfaction. J Prosthet Dent. 2000;83:521-7
47. Funke N, Fankhauser N, Mckenna GJ, Srinivasan M. Impact of shortened dental
24. Becker CM, Kaiser DA, Goldfogel MH. Evolution of removable partial denture design.
arch therapy on nutritional status and treatment costs in older adults: A systematic
J Prosthodont. 1994;3(3):158-66. doi: 10.1111/j.1532-849x.1994.tb00147.x
review. J Dent. 2023;133:104483. doi: 10.1016/j.jdent.2023.104483

CPD questionnaire on page 422

The Continuing Professional Development (CPD)

section provides for twenty general questions and five
ethics questions. The section provides members with
a valuable source of CPD points whilst also achieving
the objective of CPD, to assure continuing education.
The importance of continuing professional development
should not be underestimated, it is a career-long
obligation for practicing professionals.