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246 BRITISH DENTAL JOURNAL, VOLUME 188, NO. 5, MARCH 11 2000

PRACTICEprosthetics

Amajor concern with the use of a distal-

extension removable partial denture

(RPD) is the control of excessive torqueing

forces that may act on the abutments. To

reduce these forces, it is necessary to max-

imise support from the residual alveolar

ridges by border moulding and tissue load-

ing the impression for the altered cast pro-

cedure. It is also believed that a careful

design of the metal framework will min-imise the torque applied to the abutment

teeth. Various proposals have been made for

clasp assembly designs intended for torque

releasing effects on these teeth.1–5 In

general, these designs comprise a mesial

occlusal rest linked through a minor con-

nector, a proximal plate and a buccal reten-

tive element in a form of I-bar (RPI),1–3

L-bar (RPL)4 or Akers circumferential clasp

(RPA).5 This article suggests another design

modification pertinent to the mandibular

first premolar — a common abutment in

distal-extention RPD.

DesignCrown morphology of the mandibular first

premolar generally displays features

favourable to design of metal-framework

elements related to this tooth. First, the

non-occluding mesiolingual portion of the

occlusal table of this tooth allows for a con-

venient mesial rest seat with minimal tooth

preparation. Second, the crown is tilted lin-

gually and is usually smaller compared with

the mandibular second premolar.6,7 These

factors favour a simplified clasp assembly design for this tooth in the form of a mesial

rest, lingual bracing arm, distal guiding

plate and a buccal bracing/retentive arm.

Rest

A mesial rest seat is prepared in the

depressed mesiolingual portion of the

occlusal table of the tooth. The resulting

additional interocclussal clearance gained in

this area will accommodate adequate bulk

of metal for this component. We propose

that the mesial rest be connected to the

proximal plate with a lingual bracing arm,obviating the need for a separate minor con-

nector (Fig. 1). This modification of the

conventional design could enhance gingival

health,8–10 reduce food stagnation, and

improve patient comfort.

Lingual bracing arm

Unlike conventional designs, such as RPI,

RPL or RPA, the minor connector is

replaced by a lingual bracing arm that con-

nects the mesial rest with the distal proximal

plate(Fig. 1). As the crown of the mandibu-

lar first premolar is usually tilted lingually and the lingual height of contour is not too

bulky, 6,7 a slight reshaping of this bulk is

needed so that a rigid lingual bracing arm

The mandibular first premolar as anabutment for distal-extension removable

partial dentures: a modified claspassembly design

A. Shifman,1 and Z. Ben-Ur,2

1Senior Clinical Lecturer, Department of Oral Rehabilitation, and Chief, Maxillofacial Prosthetic Unit, Sheba Medical Center, Tel Hashomer, Israel 2Clinical Lecturer, Department of Oral Rehabilitation, The Maurice and GabrielaGoldschleger School of Dental Medicine, Tel Aviv University, Israel

Correspondence to: Dr Arie Shifman, PO Box 1031,Petach Tikva 49110, Israel REFEREED PAPER

Received 19.03.99; accepted 16.09.99 © British Dental Journal 2000; 188: 246–248

Sound mandibular first premolars can be used as sole

abutments for bilateral distal-extension removable partialdentures, if the denture is designed to minimise the torque

applied to the abutment teeth. A simplified modification of the

conventional torque-releasing clasp-assembly designs is

suggested for these teeth. This modification entails a mesial rest

on each abutment tooth connected to the distal proximal plate

via a lingual bracing arm. A circumferential clasp arm is optional

for buccal retention of the removable partial denture. As with

conventional designs, the metal framework is designed to

permit some rotational tissueward movement of the distal

extension bases, yet not compromise the retention and stability

of the prosthesis.

In brief Despite enormous progress with the use

of implants to restore posterior edentulousregions, removable partial dentures arestill a viable treatment option for somepatients.

Mandibular first premolars may often beencountered as abutment teeth for distal-extension removable partial dentures.

Many authors advocate the preferencefor mesially placed occlusal rests to thoseplaced distally theorising that suchdesigns release stress from the abutmentteeth.

A modified metal framework design isdescribed for these clinical situations.

This simplified design will notcompromise accepted principles of removable partial denture design.

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BRITISH DENTAL JOURNAL, VOLUME 188, NO. 5, MARCH 11 2000 247

PRACTICEprosthetics

can be positioned in a region congruent to

the middle and occlusal thirds of the lingual

wall. This design permits freedom for tis-

sueward movement of the lingual bracing

arm, during a rotational movement of the

distal extensions of the RPD around the ful-

crum line passing through the mesial rests

(Fig. 2). The lingual bracing arm should be

of adequate bulk to ensure its rigidity.

Guiding plate

The guiding plate is designed to contact theocclusal third of the distal aspect of the

tooth. To make the required contact, the

master cast must be surveyed with an ante-

rior tilt. The RPD will thus be given a path of

insertion and removal that is not parallel to

the long axis of the tooth(Fig. 3), thereby

enhancing retention but not compromising

the torque-releasing effect.11

Buccal retentive arm

Although any type of conventional retainer

(I-bar,1–3 L-bar4) can be used with this con-

cept, the buccal bracing/retentive arm of theRPA system (Akers circumferential clasp)5

would appear to be the most suitable for the

mandibular first premolar. The presence of

soft tissue undercuts buccally, and the

increased action of the circumoral muscula-

ture adjacent to this tooth,12 often precludes

the use of a bar clasp. When using the Akers

circumferential clasp system, it is important

that only the superior border of the bracing

component of the circumferential clasp

contacts the survey line, so as to enable the

clasp a mesiogingival rotational movement

around a mesial fulcrum line.5 This is

accomplished by a wax block-out of the area

below the survey line of the master cast

which is subsequently transferred to the

refractory cast. The anterior retentive end of

the clasp is localised in the undercut

mesially to the midline of the abutment

tooth; this area should therefore not be

blocked-out.5

A bracing component placedabove the survey line will not move in a tis-

sueward direction. It is theorised that it will

render a distal shift of the fulcrum line with

torqueing of the abutment teeth by the

retentive component of this clasp.5

CommentMany factors may be involved with the suc-

cess or failure of RPD. Adaptation problems

to this type of restoration and non-compli-

ance are common; some patients even reject

the idea of wearing a removable appliance.

In addition, it has been shown that many patients can function well without restoring

molar teeth in the shortened dental

arch.13,14 No adverse effects were found in

the long term.13,14 Therefore, patients

should be carefully tailored for treatment

with RPD. Despite enormous progress with

the use of implants to restore posterior

edentulous regions, RPD are still viable

Fig. 2 Metal framework seated on master cast.Fulcrum passes the linejoining mesial rests(arrows)

Fig. 3 Diagram ofbuccal aspect of theabutment crown withclasp assembly representing thedifference between thepath of rotation (A)

and the path ofremoval (B) dictated by the guiding plate (GP)F = fulcrum point

Fig. 1 Metalframework withmesial rest designedto eliminateseparate minorconnector

A B

GP

F

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248 BRITISH DENTAL JOURNAL, VOLUME 188, NO. 5, MARCH 11 2000

PRACTICEprosthetics

Prosthet Dent 1992; 68: 799-803.11 Osborne J, Lammie G A. Partial Dentures.

4th ed. p150 Oxford: Blackwell Scientific Publ1974.

12 Nairn R I. The circumoral musculature:structure and function. Br Dent J 1975; 139:49-56.

13 Elias A C, Sheiham A. The relationshipbetween satisfaction with mouth and numberand position of teeth. J Oral Rehabilit 1998; 25:649-661.

14 Witter D J, van Palenstein Helderman W H,Creugers N H J, Kayser A F. The shortened

dental arch concept and its implications fororal health care. Community Dent Oral Epidemiol 1999; 27: 249-258.

15 Berg E. Periodontal problems associated withthe use of distal extension removable partialdentures —a matter of construction? J Oral Rehabilit 1985; 12: 369-379.

16 Bergman B, Hugoson A, Olsson C O. A 25 yearlongitudinal study of patients treated withremovable partial dentures. J Oral Rehabilit 1995; 22: 595-599.

17 Kapur K K, Deupree R, Dent R J, Hasse A L. Arandomized clinical trial of two basicremovable partial denture designs. Part I:Comparisons of five-year success rates andperiodontal health. J Prosthet Dent 1994; 72:

268-282.18 Aydinlik E, Dayangac B, Celik E. Effect of

splinting on abutment tooth movement. J Prosthet Dent 1983; 49: 477-480.

19 Igarashi Y, Ogata A, Kuroiwa A, Wang C H.Stress distribution and abutment toothmobility of distal-extension removablepartial denture with different retainer:an in vivo study. J Oral Rehabilit 1999;26: 111-116.

treatment option for some patients,

because of the lack of invasiveness, simplic-

ity and lower costs. Good oral and denture

hygiene are of utmost importance for pre-

serving long-term service.15,16 Many

authors advocate the preference for mesially

placed occlusal rests to those placed distally,

theorising that such designs release stress-

from the abutment teeth. A 5-year clinical

study by Kapur et al.,17 found no difference

between distal-extension RPD designed in aform of RPI or a distal rest with circumfer-

ential clasps (E-type), with respect to the

effect on the abutment teeth. However, in

their study,17 second premolars were

splinted to first premolars by full coverage-

cast gold crowns, which may account for

their result.18 Clinicians debate what should

be the best design for a given situation.

However, it is common for even well

designed metal frameworks not to always fit

properly and therefore, any framework

should be examined in the mouth for seat-

ing, retention and stability, and if necessary,adjusted accordingly or remade. Also, good

mucosal support of distal extension RPD

has an indispensable role in sharing the

occlusal load, even with rigid retainers on

the abutment teeth.19

This article describes a simplified design

that does not compromise accepted princi-

ples of distal-extension RPD design. Pros-

theses made according to this design were

found to function well without any compli-

cations.

1 Kratochvil F J. Influence of occlusal restposition and clasp design on movements of abutment teeth. J Prosthet Dent 1963; 13:114-124.

2 Krol A J. Clasp design for extension-baseremovable partial dentures. J Prosthet Dent 1973; 29: 408-415.

3 Demer W J. An analysis of mesial rest — I-barclasp designs. J Prosthet Dent 1976; 36:243-253.

4 Ben-Ur Z, Aviv I, Cardash H S. A modifieddirect retainer design for distal-extensionremovable partial dentures. J Prosthet Dent 1988; 60: 342-344.

5 Eliason C M. RPA clasp design for distal-extension removable partial dentures. J Prosthet Dent 1983; 49: 25-27.

6 Wheeler R C. Dental Anatomy, Physiology and Occlusion. p217 Philadelphia: WB SaundersCo, 1974.

7 Sicher H. Oral Anatomy. 4th ed. St Louis: CVMosby Co, 1965.

8 Runov J, Kroone H, Stolze K, Maeda T, El-

Ghamrawy E, Brill N. Host response to twodifferent designs of minor connector. J Oral Rehabilit 1980; 7: 147-153.

9 Chandler J A, Brudvik J S. Clinical evaluationof patients eight to nine years after placementof removable partial dentures. J Prosthet Dent 1984; 51: 736-743.

10 McHenry K R, Johansson O E, Cristersson L A.The effect of RPD framework design ongingival inflammation: a clinical model. J

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