Support, rest and enamel modification

Question 1

What is support

Answer 1

the resistance to vertical forces acting towards the residual teeth and soft tissue

Question 2

What kind of support are there, explain the type of supports

Answer 2

Tooth support, mainly obtained from rest and rest seats, preferable to mucosal support. Periodontal membrane can cushion vertical occlusal load. Capability of load tolerance also depend on periodontal health. Molar best load tolerance

mucosal support, planned for when tooth support inadequate. Best obtained from edentulous ridges. Can be obtained from denture base

Question 3

What happens when there is insufficient support

Answer 3

underlying soft tissue damage, eventually increase bone resorption

Question 4

what is a rest

Answer 4

a small metal projection from main frame of RPD, acts as supporting element

Question 5

What must a rest be

Answer 5

must be rigid, comfortable, hygienic

Question 6

What is the point of a rest seat

Answer 6

to allow favourable tooth surface for support, to prevent interference with occlusion, to reduce prominence of rest, provide a more vertical loading on the tooth. Without it tooth will be pushed labially by rest, unnatural prominent bulge, collect food particle, irritate the tongue

Question 7

what is the function of the rest

Answer 7

To prevent impingement of gingival tissue, prevent food packing, transmit occlusal load along long axis of abutment tooth, maintain components in planned position, maintain occlusal relationship by preventing denture base from sinking, prevent denture base from displacing away from saddle

Question 8

When is enamel modification used

Answer 8

to create guide plane, create rest seat, create occlusal channel when teeth intercuspate very tightly, modify unfavourable undercuts, modify occlusal plane

Question 9

Why is the canine a good placement for rest compared to incisors

Answer 9

1. root length and form of canine tooth more suitable
2. less steep lingual surface of canine compared to incisal teeth
3. enamel thicker than incisal teeth

Question 10

How should rest seat prep look like

Answer 10

from the lingual view: a broad v shape
from the incisal aspect: broadest at the centre
from the proximal view, floor should be towards cingulum than axial wall