concepts of rpi /prosthodontic courses

CONCEPTS OF RPI

INDIAN DENTAL ACADEMY

Leader in continuing Dental Education

www.indiandentalacademy.com

CONTENTS

Introduction

IBar philosophy

RPI system

RPA system

Conclusion

Bibliography

Terminology

• REST :

a projection or attachment, usually on

the side of an object

• REST SEAT :

the prepared recess in a tooth or

restoration created to receive the occlusal,

incisal, cingulum, or lingual rest

• I-bar clasp:

the component of the clasp assembly

that engages a portion of the tooth surface

and either enters an undercut for retention

or remains entirely above the height of

contour to act as a reciprocating element.

Generally it is used to stabilize and retain

a removable dental prosthesis

INTRODUCTION

• In contrast with the Kratochvil’s basic

design, which necessitates heavy

preparation, Krol developed a modification

that avoids tooth preparation.

• The state emphasis in Krol’s system is

stress control with minimal tooth coverage

and minimal gingival coverage.

• The clasp system includes the three

elements of Kratochvil’s system: -

mesial rest,

proximal plate

and I-bar.

• Each element, however, has undergone

significant change to meet Krol’s criteria.

• In RPI system:

R = Rest

P = Proximal plate

I = I-bar

• MESIAL REST:

• I-BAR RETAINER:

• DISTAL PROXIMAL PLATE-LONG

DISTAL GUIDING PLANE THAT

EXTENDS IN TO THE TOOTH TISSUE

JUNCTION:

• Rest preparations are less extensive in the

RPI system.

• The mesial rest extends only into the

triangular fossa, even in molar

preparations, and canine rests are often

circular concave depressions prepared in

the mesial marginal ridge

• When aesthetics permits incisal rests can

be used in mandibular anteriors

• And they can be used to splint the

periodontally weakened teeth

features

• Mesial rest.

• It provides Vertical support

• Good adaptation to transfer forces

principally

• Sufficient bulk to with stand fources

• As the distance from the

denture base to teeth increase,

the associated radius also

increase and the arc or rotation

become linear, hence anterior

placement of rest help direct

the forces more vertically onto

tissues of the residual ridge

• REASONS FOR MESIAL REST:

PROXIMAL PLATE:

• The proximal plate makes greatest

departure from Kratochvil’s design.

• The prepared guide plane is 2 to 3 mm

high occlusogingivally and the proximal

plate contacts only 1 mm of the gingival

portion of the guide plane

• . Relief is provided at the tooth – tissue

junction to allow the proximal plate to

disengage into the proximal undercut

under occlusal loading.

• This proximal plate, in conjunction with the

minor connector supporting the rest,

provides the stabilizing and reciprocal

aspects of the clasp assembly.

advantages

• Improved stabilisation

• Reunites and stabilizes remaining teeth with the

dental arch

• Retention Improves by limiting the paths of

removal and insertion

• Reduces food impaction between teeth and

proximal plate and protects teeth tissue junction

• Provides reciprocation during insertion and

removal

• Distributed forces through out the archwww.indiandentalacademy.com

I – bar:

• The I-bar should be located in the gingival

thirds of the buccal or labial surface of the

abutment in a 0.001 inch undercut.

• The whole arm should be tapered into the

terminus, with no more than 2 mm of its tip

contacting abutment.

• The retentive tip contacts the tooth from

the undercut to the height of contour.

• This area of contact along with the rest

and proximal plate contact provides

stabilization through encirclement.

• The horizontal portion of the approach arm

must be located at least 4 mm from the

gingival margin and even farther if

possible.

• ADVANTAGES:

• Food accumulation minimized

• Approach arm does not contact abutment

teeth so lateral forcers are minimized.

• DISADVANTAGES:

• Less horizontal stabilization

• Less retention.

• There are three basic approaches to the

application of the RPI system.

• The location of the rest, the design of the

minor connector (proximal plate) as it

relates to the guiding plane, and the

location of the retentive arm are factors

that influence how this clasp system

functions.

• All advocate the use of a rest located

mesially on the primary abutment tooth

adjacent to the extension base area.

I approach :

• This approach recommends that the

guiding plane and corresponding proximal

plate minor connector extend the entire

length of the proximal tooth surface, with

physiological tissue relief to eliminate

impingement of the free gingival margin

• Bar clasp assembly in which guiding plane

(GP) and corresponding proximal plate

(PP) extend entire length of proximal tooth

surface to contact greater surface area of

guide plane which directs functional forces

in horizontal direction , thus tooth {teeth}

are loaded more than edentulous ridge.

II approach:

• This approach suggests that the guiding

plane and corresponding proximal plate

minor connector extend from the marginal

ridge to the junction of the middle and

gingival thirds of the proximal tooth

surface

• Both approaches recommend that the

retaining clasp arm be located in the

gingival third of the buccal or labial surface

of the abutment in a 0.001 inch undercut

• This decrease amount of surface area

contact of proximal plate on guide plane

more evenly distributes functional force

between tooth and edentulous ridge

III approach:

• This approach favours a proximal plate

minor connector that contacts

approximately 1mm of the gingival portion

of the guiding plane and retentive clasp

arm located in a 0.001 inch undercut in the

gingival third of the tooth at the greatest

prominence or to the mesial away from the

edentulous area

• During function, proximal plate and I-bar

clasp arm are designed to move in

mesiogingival direction, disengaging tooth.

Lack of sustained contact between

proximal plate and guide plane distributes

more functional force to edentulous ridge.

• Application of each approach is predicated

on the distribution of load to be applied to

the tooth and edentulous ridge.

• The stated purpose of reducing the

proximal plate is to improve gingival health

by opening up embrasure spaces as much

as possible.

• DESIGN VARIATIONS:

1. MAJOR CONNECTORS IN MANDIBLE

AND MAXILLA

2. MINOR CONNECTORS

3. DENTURE BASE CONNECTORS

MODIFICATION TO RPI

SYSTEM:

• Kroll in 1976 has given modification to RPI

system. That is

• RPA in which

R = rest

P = proximal plate

A = Akers clasp

contraindications for a bar- type

exaggerated buccal or lingual tilts,

severe tissue undercut

or a shallow buccal vestibule

and the desirable undercut is located in the

gingival third of the tooth away from the

extension base area,

• this modification to RPI i.e., RPA should

be considered.

Tipped abutments

and tissue impingements are

• treated with RPA clasp.

• When Akers clasp arm is used, careful

attention is paid to relieve all undercuts

except at the retentive tip

The removable partial denture design:

british dental journal: vol-189; n0-7 pg-

• In the study they concluded that there a plaque accumulation in terms of quality and quantity on alloplastic materials and there is some components are leached into oral cavity from this alloplastic material

• And this will cause tissue injury

• This can be prevented with the equillibrium in 3 components

• 1- operator

• 2- patient

• 3- laboratory perosenell

10yr old evaluation of r.p.d’s ,survival

rates based in re treatment

j.p.d- vol-76: no-1, 1996

• In this survey 784 patients were given with

metal dentures and their feed back was

• In the survey it was found that

88% - with 96% of success

10 people died that is 8%

Remaining people didnt wear the r.p.d

A randomised clinical trial of 2 basic r.p.d’s-

comparision of masticatory efficiency-

j.p.d- 1997: 78; 15-21

• Statement of problem: there is no clinical data about the functional efficiency of different r.p.d designs.

• For this 118 patients were selected with unilateral or bi lateral r.p.d’s

• Conclusion: despite some performance difference at entry the mean performance scores for the 2 different groups became similar

conclusion

• Successful use of the system requires

careful analysis of each component for the

function that it provides and thoughtful

execution of the system in the abutment

preparation and precise fitting of

framework

• The i-bar design meets all of the

requirements of partial denture clasp

system, horizontal stabilization, retention,

reciprocation, and passivity.

• Successful use of i-bar system requires

careful analysis and planning of each

component, skillful abutment preparation,

and precise fitting of the frame work

• Bibliography

• 1.MC CRACKEN’S REMOVABLE PARTIAL PROSTHODONTICS

11TH EDITION.

• 2.STEWART’S CLINICAL REMOVABLE PARTIAL PROSTHODONTICS

3RD EDITION.

• 3.REMOVABLE DENTURE PROSTHODONTICS –A.A GRANT /W.JOHNSON 2ND EDITION.

• 4.A COLOUR ATLAS OF REMOVABLE PARTIAL DENTURES

J.C.DAVENPORT,R.M.BASKER

• 5.REMOVABLE PARTIAL PROSTHODONTICS-DR SYBILLE K LECHNER,PROFESSOR A ROY MAC GREGOR.

REFERENCES

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