principles of design of rest seats and different types of rests

1. REST AND REST
SEATS
DR SHOAIB RAHIM
BDS, FCPS
ASSISTANT PROFESSOR

2. DEFINITION
REST
Rigid extension of a removable partial denture that contacts
the occlusal, incisal, cingulum, or lingual surface of a tooth or
restoration, the surface of which is commonly prepared to
receive it
REST SEAT
The prepared recess in a tooth or restoration developed to
receive the occlusal, incisal, cingulum, or lingual rest

3. FUNCTIONS
• Provide vertical support
• Maintains components in their planned positions
• Maintains established occlusal relationships by preventing
settling of the denture
• Prevents impingement of soft tissue
• Directs and distributes occlusal loads to abutment teeth

4. FUNCTIONS
• Prevents extrusion of abutment tooth
• Prevents ingress of food
• Provides resistance to lateral displacement
• Contributes to indirect retention

5. FORMS OF REST AND REST
SEATS
• Occlusal Rest
• Cingulum Rest
• Incisal Rest
• Implants as Rest

6. OCCLUSAL REST

7. REQUIREMENTS
• Rounded triangular
• As long as it is wide (2.5mm)
• Marginal ridge must be lowered to permit sufficient bulk of
metal for strength and rigidity (approximately 1.5 mm)
• Floor of occlusal rest seat should be apical to marginal ridge
and occlusal surface, and should be spoon shaped (2mm)
• The angle formed by occlusal rest and vertical minor connector
should be less than 90 degrees

8. TYPES OF OCCLUSAL RESTS
• Double Occlusal Rest
• Extended Occlusal Rest
• Interproximal Occlusal Rest
• Internal Occlusal Rest

9. DOUBLE OCCLUSAL REST
• More than 90 degree angle
• Mesial and distal side
• Lone tilted abutment
• To support ring clasp

10. EXTENDED OCCLUSAL REST
• Kennedy Class II, modification 1 and Class III situations with
mesially tipped molar

11. MODIFIED EXTENDED
OCCLUSAL REST
• Severely tilted abutment
• In the form of an onlay to restore occlusal plane
• 1-2 mm bevel on buccal and lingual occlusal surface to provide
stabilization
• 1-2 mm guiding plane on mesial surface of abutment

12. INTERPROXIMAL OCCLUSAL
REST
• Prepared as individual occlusal rest seats but with extended
lingual preparation
• Prevent food impaction

13. INTERNAL OCCLUSAL REST
• Tooth supported cast partial denture
• Occlusal support and horizontal stabilization
• Support derived from floor
• Horizontal stabilization derived from near vertical walls
• Outline form is slightly dovetailed
• Elimination of buccal clasp and favorable rest seat location

14. IMPLANT AS REST

15. • Advantage of vertical stiffness
• Prevent tissue-ward movement
• Also provide retention
• Low profile connection
• Alter or eliminate fulcrum location for prosthesis movement

16. SUPPORT FOR RESTS
• Made on sound enamel or any restoration material
• If fissures are found on occlusal surface then they should be
removed and restored first
• Best abutment for cast partial denture is protected abutment
• Preparation with burs and polishing points

17. SUPPORT FOR RESTS
• Rest seats in crowns and inlays are somewhat larger and deeper
• Rest seats for tooth-supported dentures may be made slightly
deeper than those that support a distal extension base
• Internal rest seats are created first in wax, either with suitable
burs in a handpiece holder or by waxing around a lubricated
mandrel

19. LINGUAL REST

20. JUSTIFICATIONS
• Anterior tooth may be the only abutment available for occlusal
support
• Anterior tooth occasionally may be used to support an indirect
retainer or an auxiliary rest
• Root form, root length, inclination of the tooth, and crown to
root ratio must be considered
• Lingual rest is preferable to incisal rest because it is placed
closer to horizontal axis of rotation of abutment

21. REQUIREMENTS
• Rounded V shape at junction of gingival and middle third
• Mesiodistal length 2.5-3 mm, labiolingual width 2 mm and
inciso-apical depth 1.5 mm
• Prepared with inverted cone followed by tapered stones
• Prepared according to path of insertion

22. MODIFICATIONS/
ALTERNATIVES
• Most satisfactory lingual rest from standpoint of support is one
that is placed on prepared rest seat in cast restoration
• Maybe placed on lingual surface of cast veneer crown, a three-
quarter crown, inlay, laminate veneer, composite restoration, or
etched metal restoration
• Conservative restorations in anterior teeth may be better suited
for ball types of rest seats than inverted V types of rest seats
• Sapphire ceramic orthodontic brackets bonded to lingual
surfaces of mandibular canines and shaped as rest seats maybe
used

23. INCISAL REST

24. RECOMMENDATIONS
• Placed at the incisal angles of anterior teeth
• Provides definite support with relatively little loss of tooth
structure and little display of metal
• Used predominantly as auxiliary rests or as indirect retainers
• More likely than lingual rest to lead to some orthodontic
movement of tooth because of unfavorable leverage factors
• Prepared in the form of a rounded notch at the incisal angle
with deepest portion of the preparation apical to incisal edge

25. RECOMMENDATIONS
• Notch should be beveled both labially and lingually
• Lingual enamel should be partly shaped to accommodate the
rigid minor connector
• Width should be 2.5 mm and depth should be 1.5 mm
• Incisal rest should be over-contoured slightly to allow for labial
and incisal finishing to the adjoining enamel

26. JUSTIFICATIONS
• They may take advantage of natural incisal faceting
• Tooth morphology does not permit other designs
• Such rests can restore defective or abraded tooth anatomy
• Incisal rests provide stabilization
• Full incisal rests may restore or provide anterior guidance

27. THANK YOU