Rest and Rest Seat

Question 1

What is a rest?

Answer 1

Component of an RPD in contact with tooth surface that provides vertical support and transmits occlusal load to the abutments.

It is a rigid structure that is part of the metallic infrastructure

Question 2

What is a rest seat?

Answer 2

A prepared surface on the abutment to receive the rest

Question 3

What should the topography of the rest look like?

Answer 3

Topography of the rest should restore the topography of the tooth before the rest seat preparation.

Question 4

What are the primary functions of the rest?

Answer 4

Provide vertical support (occlusogingival direction)

To direct and distribute the occlusal load to abutment teeth

Question 5

What are the secondary functions of the rest?

Answer 5

To maintiain components in their position and promote stabilization and retention: Neutralizing rotational movements.

To maintain established occlusal relationships

To prevent impingement of soft tissues

To maintain the correct relationship clap and abutment

To restore occlusal plane discrepancies

Question 6

What is the most appropriate direction for occlusal load on abutment teeth?

Answer 6

The axial direction (If the tooth is stressed along its long axis without damaging abutment teeth)

Question 7

Where are rest seats able to be located?

Answer 7

Occlusally

Lingually

Incisally

Question 8

What is the type of rretentions that rests can provide?

Answer 8

Can be direct or indirect retention

Question 9

What shape should occlusal rests be?

Answer 9

Rounded triangular shape

Question 10

How wide should the occlusal rests be?

Answer 10

Width half that of the intercuspal distance

Question 11

How far Mesiodistally should the occlusal rest be?

Answer 11

M/D equal or larger than the B/L size.

Question 12

What shape should the floor of the occlusal rest preparation be?

Answer 12

Cocave and rounded and slightly inclined apically (Less than 90 degrees).

Question 13

How thick should the rest be?

Answer 13

0.5mm thick closer to the tip and 1 - 1.5mm thick at the marginal ridge.

Question 14

What are the features of a good occlusal rest/rest seat?

Answer 14

Rounded triangular shape

Width (B/L) 1/2 of intercusapl distance

M/D equal or larger than B/L size

Floor is concave/rounded

Slight incline apically

0.5mm thick at its point and 1.0 - 1.5mm thick at the marginal ridge

Deepest part of the rest seat is close to the long axis

Normal occlusal contact

Question 15

What are the features of the lingual/cingulum rest?

Answer 15

Should lie on the cingulum of anterior teeth.

Convex M/D

Concave B/L (V shaped)

Floor less than 90 degrees

Rounded, no sharp line angles

Minimum reduction 0.8mm

Normal occlusal contact

Question 16

If there isn’t enough space for a rest seat how can more space be created?

Answer 16

Using composite lingually/palatally

Question 17

What are the features of the incisal rest/rest seat?

Answer 17

Concave M/D

Convex B/L

Floor <90 degrees

From L to B

Rounded with no sharp angles

2.5mm wide and 1.5mm deep

Question 18

When do we use an incisal rest seat?

Answer 18

Occlusal interference of lingual rest

Question 19

What are the disadvantages of the incisal rest seat?

Answer 19

Poor aesthetic

Unfavourable biomechanics

Occlusal interference

Question 20

Where are the direct retaining clasps located?

Answer 20

Adjacent or near the edentulous area

Part of the retentive clasp

Question 21

What is the function of the indirect retaining clasps located?

Answer 21

Part of a clasp or just the rest

Prevent rotation of the denture

Distant from the fulcrum line

Question 22

What happens if the stress is oblique instead of apical?

Answer 22

The most effective resistance is provided if the tooth is stressed along its long axis, without damaging the abutment.

Stress obliquely along the periodontal ligament will lead to bone loss and mobility because pressure causes bone resorption.

Question 23

Where, relative to the edentulous area, should the rest be placed?

Answer 23

Always place rest adjacent to the edentulous area except in a free end saddle, then it should be moved more distant to the edentulous area.

Question 24

What about class 4 dentures How should rests be placed for them?

Answer 24

Anterior teeth are treated like free end saddle. Place the rests on the distal side instead of mesial side.