rest seat and rest seat preparation - faculty.psau.edu.sa · indirect retainer). •rest designated...

Rest Seat And

Rest Seat PreparationPresented by:

Dr. Tushar Bhagat

BDS, MDS (Prosthodontics)

Diploma in Advance Implantology (Romania)

Content & References

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• Definition of rest seat (B.p.no.67)

• Purpose of rest seat (B.p.no.67)

• Types of rest seat. Primary & Auxiliary Rest seat (A.p.no.44)

• Various forms of rest seat

– Occlusal rest & rest seat (Proximal RS, Long occlusal RS, Embrasure RS)

(A.p.no.44-47; B.p.no.68-71)

– Lingual or cingulum RS (Inverted “V” RS, Ledge RS, Ball RS) (A.p.no.47-48;

B.p.no. 76-78)

– Incisal RS (A.p.no.48-49)

• Re-contouring / Enameloplasty & Dimpling (Stewart’s-p.no.286)

• Definition

• Reasons for re-contouring

• Dimpling

Introduction

• Rest is a component of a direct RPD (direct &

indirect retainer).

• Rest designated by the surface of the tooth

prepared. (occlusal rest, incisal rest etc.)

3

lingual

buccal

Retentive arm

Bracing arm

Definition

• Rest: The component of RPD that transfer

forces down the long axis of the abutment teeth

are called as Rest.

4

Ref: Stewart’s Removable partial prosthodontics. P.n.43

Definition

• Rest seat: the prepared surface of teeth into

which rest fits are called as Rest Seat.

5


Lect.No.4. Abutment

teeth preparation.

Types of Rest Seat

1) The rest that is part of retentive clasp assembly is

referred as primary rest seat.

2) The rest that is additional support or indirect retainer

retention is called auxiliary rest or secondary rest.

6


auxiliary rest primary rest seat.

Primary rest seat

• Prevents vertical movements of prosthesis towards

tissues.

• Transmit applied forces to supporting teeth.

• Seat should be shallow & saucer shape so that it should

function like ball and socket joint

7


Auxiliary rest seat

• Used as indirect retainers in extension base RPD

(Class I, II & long span Class IV)

• Placed anteriorly or posteriorly to the axis of rotation to

prevent extension bases from lifting away from

underlying ridge.

8


Purpose of rest

1) Maintained component in planned position.

2) Maintain established occlusal relationship

by preventing settling of the denture.

9

Ref: McCraken Removable partial prosthodontics. P.n.67.

Purpose of rest

3) Prevent impinging of soft tissue.

4) Direct and distribute occlusal load to

abutment teeth.

10

Ref: McCraken Removable partial prosthodontics. P.n.67.

Function of rest seat

1) To maintain a planned clasp-tooth

relationship.

2) To prevent extrusion of abutment teeth.

11Lect.No.4. Abutment

teeth preparation.

Function of rest seat

3) To provide positive reference seats in

rebasing and/or impression procedures.

4) To serve as an indirect retainer by

preventing rotation of the partial denture

(Class I or II RPD’s only).


teeth preparation.

Criteria for preparation of rest

seat

High speed hand piece with coolant.

Light pressure while preparing seat.

Good visibility.

Preparation entirely in enamel, (better avoid

anaesthesia).

Medium round bur (diamond or carbide.)

13

Types of rest seat

A. Occlusal rest seat

B. Lingual / cingulum rest seat

C. Incisal rest seat

D. Intracoronal / precision rest

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Posterior rest seat

I. Occlusal rest seat Proximal RS

II. Long occlusal rest seat

III. Embrasure rest seat

Posterior tooth rest seat form

• Rest should not be placed on

inadequately prepared tooth.

• Outline form is triangular with base

of triangle located at marginal

ridge & the rounded apex directed

toward the centre of tooth.

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• Shape should follow outline of

mesial or distal fossa.

• Should occupy 1/3rd to 1/2 the

mesiodistal diameter of tooth.

• And approx. ½ the buccolingual

width of the tooth measured from

cusp tip to tip. 17



• The floor of the rest seat must

inclined slightly towards the centre

of tooth.

• Floor should be concave or saucer

shape.

18



• The most common mistake

insufficient reduction of marginal

ridge.

• 1.0 – 1.5mm thick where it crosses

marginal ridge.

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Proximal rest seat

• The preparation is at least 1.0 mm deep with a

slightly deeper portion (0.5 mm) called the

POSITIVE SEAT located toward the center of

the preparation.


teeth preparation.

Embrasure occlusal rest seat

• The EMBRASURE OCCLUSAL REST is

located in a fossa adjacent to another

tooth .

• Its size, shape and dimensions are

similar to the proximal occlusal rest

preparation EXCEPT that the flare of the

facial margin is limited by the proximal

contact with the adjacent tooth21

Long / extended occlusal rest seat


teeth preparation.

Anterior rest seat

Lingual / cingulum rest

•Preferable placed on maxillary canine.

Incisal rest

•Placed on anterior teeth.

23

Ref: Stewart’s Removable Prosthodontics. P.no.47


seat

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Placed on the lingual surface of maxillary

canines and incisors and in maxillary and

mandibular surveyed crowns.


seat

25

Rarely use on natural mandibular

incisors and canines because

there is usually insufficient

enamel thickness for an adequate

lingual rest preparation.


seat

26

Often requires for indirect retention.


seat

27

There are three types of lingual rest

preparations based on their shape:

Inverted V shaped

Ledge shaped

Ball rest seat

Inverted ‘V’ rest seat 28

This type of rest are made in canines and

incisors having a prominent cingulum.

They follows the contours of the cingulum.

Shape is usually ‘V’ when viewed from the

lingual.


The floor of the inverted ‘V’

rest seat preparation is placed

in the bulk of the cingulum.

The floor is deepest toward the

center of the tooth thus

forming a positive faciolingual

seat.


Preparation extends more cervically on

the mesial and distal thus forming a

positive mesiodistal seat.

The preparation extends through the

marginal ridges.

The cingulum shaped rest preparation

is approximately 1.0 mm deep pulpally

and cervically.

Ledge / Cingulum ledge

rest seat

Usually prepared on lingual

surface of maxillary anterior teeth.

Step like preparation from mesial

to distal.

The opposite ridge should not be

reduced.

31


rest seat

1.5 mm deep,

Should be perpendicular to the

long axis of the tooth,

Location at the junction of the

middle & gingival 3rd of the tooth.

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rest seat No undercut on labial wall.

Sharp line angle should be avoided.

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Ball rest seat

Ball rest seat is preferable used as

auxiliary rest or indirect retainer.

It can be given in both maxillary &

mandibular anterior.

At the cingulum.

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Ball rest seat 35

Anterior rest seat


• Inverted V

• Cingulum Ledge

• Ball rest seat

Incisal rest

• Placed on anterior teeth.

36

Incisal rest seat

Incisal rests are placed on the incisal edges of

mandibular incisors.

They are not placed on maxillary incisors

because the minor connector of the rest would

interfere with occlusion and the facial portion

of the rest would be very visible and

unaesthetic.

37

Incisal rest seat

Incisal rests are usually located in

the mesial or distal half of the tooth.

The rest should also be located so

that it will direct forces parallel to

the long axis of the tooth when

occlusal forces are applied to the

prosthetic teeth.

38

Incisal rest seat

The mesiodistal dimension of the rest

preparation should be 1.5 – 2.5 mm and the

depth at least 1 mm to provide adequate space

for a bulk of metal for the rest

39

Guide plane preparation

Define as, two or more parallel, vertical surfaces of

abutment teeth, so shaped to direct the prosthesis

during placement & removal.

40

Ref: McCraken Removable Prosthodontics. P.no.155

Rule for Guide plane

preparation

Proximal guide plane surface should be 1/3 to 1/2

distance between buccal & lingual cusp.

Vertically minor connector contact enamel of tooth

on proximal surface about 2/3 its length.

41

1/3 to 1/2

Buccal

Lingual 2/3 its length

Function of Guide plane

I. To provide for one path of placement & removal

II. To ensure the intended action of reciprocal,

stabilizing & retentive components

III. To provide stabilization against horizontal rotation

of dentures.

IV. To eliminate gross food entraps between

abutment & component of RPD.

42

Ref: McCraken Removable Prosthodontics. P.no.155

Enameloplasty

Conservation must be rule when

doing recontouring enamel surface.

Used to create retentive undercuts

Term used as “Dimpling”

Depression approximately 4 mm MD

& length occlusogingival height

43

Ref: Stewart’s Removable Prosthodontics. P.no.286

Thank You 44

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