This document discusses the components and design of an I-bar removable partial denture (RPD). It begins by defining RPI, which stands for rest, plate, and I-bar clasp. It then describes the key components of an I-bar RPD including mesial rests, proximal plates, and a modified I-bar retainer called the RPI system developed by Krol. The RPI system aims to reduce tooth coverage and stress compared to a standard I-bar by modifying the rest, plate, and I-bar clasp design.

2.  Introduction
 Direct retainers
 Clasps
 I bar removable partial denture
 RPI

3. RPI stands for:
R Rest
P Plate (proximal)
I I bar clasp

4. It is that component part of a RPD that is used to
retain and prevent dislodgement, consisting of a
clasp assembly or a precision attachment – GPT
TYPES OF DIRECT RETAINERS
INTRACORONAL RETAINERS EXTRACORONAL RETAINERS
-External attachments - Occlusally approaching ( Aker’s
-Internal attachments clasp)
-Stud attachments -Gingivally approaching ( bar or
-Bar attachments roach type of clasp)
-Special attachments

5. Types on the basis of design
Circumferential or Akers Vertical projection or Bar or
clasps: roach clasps:
-Simple circlet - T clasp
-Reverse circlet - Modified T clasp
-Fish-hook or hairpin - Y clasp
-Embrassure clasp - I clasp and I bar
-Multiple circlet
-Ring clasp
-Commbination clasp

6.  It is a special type of removable partial denture
 Designed by Kratochvil in 1963
 To reduce tooth contact of the retainer.
I-Bar clasp system: mesial
rest, I-bar retainer and
long guide plane.

7. I- Bar RPD Regular RPD
1. Mesial rest instead of distal rest. In 1. Distal rest
other words, the rest is on proximal side
away from edentulous space.
2. I- bar retainer is used for 2. Occlusally approaching
direct retention. retainer is used
3. Long guide planes 3. Normal guide planes
extending into tooth tissue
junction

8.  I-Bar Partial denture components:
I. Rest
II. Proximal plates
III. Major connectors
IV. Minor connectors
V. Denture base connectors
VI. Retainers

9.  Function of rest
a) Provide vertical support
against occlusal forces and
b) Control the relationship of
the prosthesis to
supporting structures.
 In order to perform this
function  rests must be of Mesial Rest
sufficient bulk  to
withstand direct occlusal
force and also the indirect
force that they are subjected
to as fulcrum points.

10.  Anterior rest must meet the basic
requirements of:
a) Strength & positiveness.
b) Esthetic considerations.
 Ideal anterior rest  crescent
shaped cingulum rest provides
maximum stabilization.
 Cingulum rest can be prepared
directly in enamel on bulky
canines and maxillary central Cingulum rest for both
maxillary and
incisors or can be implemented mandibular anterior
with a cast restoration. teeth.
 The incisal rest is used on
mandibular anterior teeth when
esthetics allow.

11.  Posterior rests 
designed to direct
vertical forces along
the long axis of tooth;
a) Premolar rests are
prepared in marginal
triangular ridges, and
b) Molar rests extend
into the central fossa.
 The rests have a ball-
shaped terminus that
allows ball-and-socket
movement around the
axis of rotation.

12.  In distal extension cases the most distal rests are
placed on the mesial aspect of the abutment teeth for
the following 2 reasons:
1. Anterior placement of the rest (fulcrum) helps
verticalize the forces of occlusion on bearing mucosa
under the denture base extension.
2. The mesial rest directs tipping forces on the
abutment mesially and tends to move the abutment
tooth into firm contact with the support of the
anterior teeth.

13.  Additional proximal plate on distal surface.
 The proximal plate covers the guide plane from marginal ridge to the
tooth tissue junction and extends onto the attached gingiva for 2mm.
a b
a. Extention of proximal plate in conventional RPD
b. Extension of proximal plate in an I-bar RPD

14.  Advantages:
i. Provides horizontal stability.
ii. Reunites & stabilizes the arch
iii. ↑ retention because of parallelism and because
dislodgement is limited to the path of insertion.
iv. Protects the tooth-tissue junction by preventing
food impaction and because of mental coverage
in the area
v. Provides good reciprocation
vi. Distributes occlusal force throughout the arch.

15.  Retention in most partial denture clasps is achieved with a
retentive arm that engages an undercut on an abutment tooth.
 In the conventional sense the I-bar provides retention against
vertical displacement, but this retention is augmented
considerably by the parallelism of guide planes that, in most
situations, limit displacement to the path of insertion.
 The I-bar is an infra-bulge retainer with a configuration designed
to minimize the deleterious effect that over-contoured retainers
have on the health of both tooth & gingiva.

16.  The arm is long and tapering
with a half-round cross-
section.
 The tip which flexes, engages
an undercut at the height of
mesio-distal contour.
 Proper positioning of I-bar
allows the tip to move
passively into the mesial
embrassure space when the
extension base recieves
occlusal loading. The I-Bar retainer should extend
2mm above the gingival margin to
engage an undercut mesial to the
 The retainer engages the mesio-distal height of contour.
undercut area & resists
vertical displacement.

17.  Advantages of I-bar configuration:
1. Because tooth contour is not altered , food
accumulation against the tooth surface is minimized.
2. I-bar is passive in relation to the abutment tooth
except against vertical displacing forces.
 Disadvantages:
1. Reduced retention
2. Less horizontal stability than other retentive
elements.

18. Other parts
 Major connector
 Minor connectors
 Denture base connectors

19.  Rest, Proximal plate and I bar
 Rest, Proximal plate and Aker’s
clasp

20.  RPI is a modified I-bar retainer system.
 Krol devised it in 1973.
 All the components of the I-bar assembly were
modified significantly to fulfill Krol’s design.
 Principle of Krol’s design was – “Stress control with
minimal tooth & gingival coverage”.

21.  The speciality of these dentures is that the direct
retainer is modified such that the retentive and
reciprocal units of the clasp act in the mesio-distal
direction ( in conventional design the retentive &
reciprocal units act buccolingually).
 The advantage of adopting this design is the minimal
tooth contact. Coverage produced by it.
 Hence, these dentures are more easy to maintain.

22. Modification of each component of
I-bar retainer required to form RPI
system
 MESIAL REST MODIFICATION
 PROXIMAL PLATE MODIFICATION
 I-BAR MODIFICATION.

23.  The mesial rest
extends only into the
triangular fossa even
in molar preparations.
Conservative rest seat preparation
 The canine rests are limited to triangular fossa
circular, concave
depressions prepared
on the mesial
marginal ridge.
 It does not cover the
entire marginal ridge. Conservative circular lingual rest used
instead of the usual cingular canine rest

24.  One of the major disadvantages of the I-bar denture
was the excessive tooth contact produced by the extra
long proximal plate.
 Krol introduces 3 modifications to the proximal plate.
 Any one of these modifications may be followed while
designing an RPI retainer.

25.  The 3 different design modifications of the proximal
plate are:
i. Design modification I
ii. Design modification II
iii. Design modification III

26.  Here the proximal plate is designed to extend from the
marginal ridge to the junction between the middle &
cervical third of tooth (remember in an I-bar retainer
the proximal plate extends about 2mm across the tooth
tissue junction).

27.  Here the proximal plate is
designed to extend along the
entire length of the proximal
surface of the abutment with a
minimum tissue relief.
 A relief is provided near the
gingival margin at tooth tissue
junction.
 This allows the proximal plate
to disengage into proximal
undercut during occlusal
overloading.

28.  Here, the proximal plate
is designed to contact
just about 1 mmof the
gingival third of the
guiding plane of the
abutment tooth.
 The purpose of reducing
the length of the
proximal plate is to
improve the gingival
health.

29.  The tip of the I-bar is modified to
have a pod-shape in order to allow
more tooth contact.
 It is placed more mesially so that it
shifts towards the mesial
embrasure space under occlusal
load and increases reciprocation.
Pod shaped I-bar retainer of
RPI system
 The I- bar is designed to
compensate for the decreased
encirclement (tooth
contact), provided by the proximal
plate & mesial rest.

30.  Clinical removable partial prosthodontics
– Stewart Rudd Kuebker
 McCracken’s removable partial prosthodontics
- Alan B. Carr
- Glen P. McGivney
- David T brown
 Internet

31. Thank You
..!!