The document discusses the design and preparation of rest seats for partial dentures. It describes that rest seats provide vertical support and are prepared on abutment teeth to receive rests. Key points include: 1. Rest seats are typically prepared as rounded triangular shapes on the occlusal surface at the middle third of the tooth. 2. They are modified to blend with the tooth contour and prevent food packing. Proper preparation involves removing enough enamel for the rest thickness without undercuts. 3. Rest seats transfer forces along the tooth's long axis, prevent extrusion, and act as indirect retainers or stops for partial dentures.

3.  Means of Support
 Means of Connection
 Means of Retention
And
 Means of Reciprocation / Bracing

4. ‹
‹WHY?
Increase masticatory efficiency

5. Support!
How?

6.  Hard tissue support (teeth)
 Soft Tissue support (Mucosa)

7. REST
Occlusal
Incisal
Cingulum

8. “Any component of a partial denture on a tooth
surface that provides vertical support is called a
rest”

9.  Primary Rest:
A rest that is part of a retentive clasp is referred to
a primary rest
 Auxiliary Rest:
A rest that is responsible for additional support or
indirect retention is called an auxiliary rest or
secondary rest

10.  Portion of a tooth prepared to receive a rest

11.  1.
 occlusal rest placed at the
arrow
 2.
 create a premature contact
 3.
 unless a rest seat was
prepared

12.  1. Direct forces along long axis of abutment

13.  2. Prevents denture base from moving cervically
& impinging gingiva

14. Major connector imbeds into tissue

16.  3. Maintain a clasp -tooth relationship

17.  4. Prevent extrusion of abutments
 5. Provide reference for relines or
impressions

18.  6. Act as indirect retainer
◦ Prevents rotation (Class I or II RPD’s only)

19.  Rounded triangular shape
◦ Apex near center of tooth

20.  Base of triangle should be one third the
bucco-lingual width of the tooth

21.  Floor inclined towards the center
 Angle formed by rest and minor connector
should be less than 900

22.  Marginal ridge must be lowered and rounded
1-1.5mm
◦ Bulk of metal to prevent fracture

23.  Adjacent teeth, the form is also modified
 Flared more on facial and lingual line
angles

24.  Deepest portion is central

25.  An explorer tip will not slide off the rest seat

26.  Usually the canine, due to its well-developed
cingulum
 When canine is not available, an incisor may
be used

27.  Inverted “V”
 < 900

30.  Slightly rounded to avoid sharp line angles
 Test as ‘positive’ with explorer tip
 1mm depth

33.  Do not create an enamel undercut
 Cylindrical bur along the long axis of the
tooth

34.  Light pressure
 High-speed handpiece
 +/- Waterspray
 Minimal heat is generated

35.  Chromium-cobalt lingual rest seat on
mandibular canine retained by resin cement
with acid-etched tooth preparation.

36. Preparation on mandibular premolar for surveyed crown incorporates
space for mesio-occlusal rest seat. Adequate occlusal reduction
was accomplished to accommodate the depth of the rest seat in the
abutment crown. The modification for the rest seat is performed
following the standard crown preparation.

40.  1 – rest placed on an
unprepared tooth
surface tend to collect
food particles
 2 – rest seat allow the
rest to be shaped so
that it blends into the
contour of tooth

41.  The designof rest seats on
post teeth
 1 – occlusal view
 2 – mesiodistal view
 3 – proximal view
 Rest seat of post teeth
should normally be saucer-
shaped
 Use of a box-shapes rest
seat within a cast
restoration result in rest
applying damaging
horizontal loads on the
abutment tooth(restricted
to tooth -supported
dentures where the perio
health of the abutment
teeth is good

42.  Rest should be at least
0.8 -1mm thick for
adequate strength. Pt
asked to occlude on a
strip of softened pink
wax. The thickness of
wax in the region of
rest seat indicate
sufficient enamel has
been removed

43.  On maxillary ant teeth,
 particularly canines ,
the cingulum is often
well developed so that
modest prep to
accentuate its form
creates a rest seat w/o
penetration of enamel
 A cylindrical green
stone with a rounded
tip should be used.
 A spherical instrument
tends to create
unwanted undercuts.

44.  Preparation for Preparation
for mandibular
 anterior tooth is shown
from
 the:
 1 – labial viewpoint
 2 – lingual viewpoint
 3 – proximal viewpoint
 Incisal rest seat can be
 prepared using a
tapered
 cylindrical diamond

45.  Vertical stop
 Transfer of forces
 Indirect retainer
 Position of Clasp
 Tipped Abutment
 Prevent extrusion
 Prevent sinking of denture
 Prevent food packing
 Forms lost tooth surface

47.  Posterior abutment
 Long axis of tooth
 Boxed vs rounded

48.  Spoon shaped
 Rounded triangle
 Middle 1/3 of occlusal surface
 Central portion deeper than marginal ridge