REST AND REST SEATS PPT [Autgvhgvosaved].ppt

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1. RESTS AND
REST SEATS

2. DEFINITION
According to Glossary of Prosthodontic Terms-
1. Rest - is a rigid extension of a fixed or a removable partial
denture which contacts remaining teeth to dissipate
vertical or horizontal forces.
2. Rest seat - is the portion of a natural tooth or a cast
restoration of a tooth selected or prepared to receive an
occlusal, incisal, lingual, internal or semiprecision rest.

3. According to McCracken’s -
1. Rest - Any unit of a partial denture that rests on a
tooth surface to provide vertical support.
2. Rest seat - The prepared surface of an abutment to
receive the rest

4. FUNCTIONS OF THE RESTS
•The primary purpose of the rest is to provide vertical support
for the partial denture and thus resist the movement in a
cervical direction .
•It maintains components in
their planned positions

5. • It transmits vertical load as well as the horizontal
forces to the tooth.

6. • Directs and distributes occlusal loads to
the abutment teeth and directs forces in the
long axis of the teeth

7. •Provides rigid prosthetic support.
•Maintains established occlusal relationships by preventing
settling of the denture.
•Prevents supra eruption.

8. •Deflection of food by bridging the gap
between two teeth

9. •Prevents impingement of soft tissues.
•Protects the denture/abutment tooth junction.

10. GENERAL CONSIDERATIONS FOR RESTS AND REST SEATS
Rests act as a vertical stop to
prevent injury to soft tissues
under partial denture.
A large occlusal onlay rest can
be contoured to re-establish
the occlusal plane of a tilted
abutment tooth.
There should be slight
movement within the rest seat
to dissipate horizontal forces
and protect the abutment
teeth.

11. Floor of the recess
should be less than 90°
to the long axis of the
tooth- to direct stresses
axially.
It is apical to the
marginal ridge.

12. Rests should be placed
on the proximal surfaces
of all the teeth adjacent
to edentuluous space.
Rest should not be
placed on inclined tooth
surfaces.
A rest & a minor
connector can be used
for reciprocation.

13. Rounded in all aspects (no
sharp line angles).
Minimal preparation in
dentin.
Center is deeper than the
surrounding rest surface.

14. Placed as close to the
gingiva and bone as
possible to reduce
leverage.

15. CLASSIFICATION/TYPES
According to McCracken, on the basis of the position of
the rest of the abutment -
Occlusal - Placed on occlusal surface of a posterior tooth.
Cingulum or Lingual – Placed on lingual surface of a tooth.
( maxillary canine)
Incisal – Placed on the incisal edge of the tooth.
(mandibular canine and incisors)

16. According to Stewart, on the basis of the relation of the rest to
the direct retainer -
Primary Rests – Rests placed along with the clasp
assembly. Used for direct retention.
Secondary or Auxiliary Rests – Rests placed for indirect
retention, away from the clasp.

17. Occlusal Rest Seat Form
Rounded triangular shape
Apex near center of tooth
Base of triangle should be one third the
bucco-lingual width of the tooth

18. Occlusal Rest Seat Form
Floor inclined towards the center
Angle formed by rest and minor
connector should be less than 90
0

19. Double Embrasure Rest Seat
Form
Adjacent teeth, the form is also
modified
Flared more dramatically on facial
and lingual line angles

20. Cingulum rest
seat form
Usually the canine, due to its well-
developed cingulum
When canine is not available, an incisor
may be used
Slightly rounded to avoid sharp line angles
Test as ‘positive’ with explorer tip
1mm depth

21. INCISAL REST SEAT FORM
It should appear as a small, v shaped
notch located approximately 1.5 to 2
mm from the proximal-incisal angle
of tooth

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