This document discusses partial denture rests and their role in supporting partial dentures. It describes the different types of rests used for anterior and posterior teeth. Anterior rests include crescent-shaped cingulum rests, circular concave rests, and incisal rests. Posterior rests are designed to direct forces along the tooth's long axis to preserve remaining structures. Continuous posterior rests can also stabilize periodontally compromised teeth. Proper rest design and tooth preparation are necessary to create positive, supportive engagement between the partial denture and abutment teeth.

1. Partial Denture Rests
John Beumer III
and
Ting Ling Chang
Distinguished Professor Emeritus
Division of Advanced Prosthodontics, Biomaterials
and Hospital Dentistry
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2. Partial Denture Rests
Primary role
 Support (resist
the forces of
occlusion)
Secondary
roles
 Reciprocation
 Bracing
 Restore the
occlusion

3. The concept of the positive rest:
The primary function of rests is to provide support.
Therefore the rest must be engage the tooth in a
positive fashion

4. The concept of the positive rest:
 The rest must not permit the prosthesis to slide off the
tooth or allow the tooth to move out of existing relationship to
other teeth as occlusal pressure is increased.

5. Partial denture rests
Positive rests preserve the remaining oral
structures by:
 Controlling the position of the prosthesis in relation to the
teeth
 Controlling the position in relation to the periodontium and
mucosa
 Controlling the amount and direction of movement of the
abutment teeth

6. Partial denture rests
 The rest must be positive.
 If the rest is not positive the abutment teeth will be
displaced and be subjected to undesirable torquing
and tipping forces as seen in this instance
 The result may be premature loss of the abutment
tooth.

7. Partial denture rests
 In this example when an occlusal force is applied in
the extension area, the RPD will rotate around the
distal portion of the abutment and the retainer will pull
the tooth upward and posteriorly

8. Rests
 Rests should be designed to direct occlusal forces
(arrow) along the long axis of the tooth

9. Rests
Determine the axis of rotation
 Their position in
extension based
RPD’s determine
the axis of rotation
(fulcrum lines)
(dotted line)

10. Anterior rests
Types
 Incisalrests (A)
 Circular concave rests (B)
 Crescecnt shaped
cingulum (C)
A B C

11. Anterior rests
Basic general requirements
 Anterior rests should be contoured to
engage the abutment tooth in positive
fashion so that the occlusal forces
are directed along their long axis
 They should provide support for the
RPD without inducing tipping forces
(A) Circular concave (B) Incisal (C) Cingulum

12. Anterior rests
Basic general requirements
 They are contoured so that when there is increased force
applied to the prosthesis, the rest will engage securely
and direct occlusal forces along the long axis of the tooth

13. Anterior rests
Basic general requirements
They are contoured so that when there is increased force
applied to the prosthesis, the rest will engage securely and
direct occlusal forces along the long axis of the tooth

14. Anterior rests
Rests should not be placed on
inclined surfaces of anterior
teeth in such a way that the
abutment tooth is exposed to
lateral forces. This may result
in:
 Tooth displacement
 Bone loss around the abutment
 Tissue displacement and
destruction
 Disruption of the occlusion

15. Crescent shaped cingulum rests
Commonly used on maxillary cuspids and centrals
 Often can be carved into existing virgin maxillary central
incisor or canine

16. Crescent shaped cingulum rests
 Difficult to use on mandibular teeth without preparing a
three quarter or full veneer crown as is seen in this patient
*The incisal rest is more commonly used in mandibular anterior teeth

17. Crescent shaped cingulum rests
Basic general requirements – Crescent shaped
cingulum rests
 The center is deeper than the surrounding surface

18. Crescent shaped cingulum rests
Basic general requirements
 They are rounded in all aspects (no sharp
angles)
 There is easy access for impression making

19. Crescent shaped cingulum rests
Basic general requirements
 They are contoured to form a half circle (especially for
extension situations)
 There are no undercuts
Occlusal force
Extension base

20. Crescent shaped cingulum rests
Basic general requirements
 Is placed as close to the periodontium as possible to
reduce leverage of the abutment

21. Crescent shaped cingulum rests
Basic general requirements
 If possible it is positioned in line with the residual ridge
for extension base RPD
 It is contoured so that the RPD casting rotates freely
around the rest when an occlusal forces is applied
Occlusal force
Extension base

22. Anterior rests
Methods of creating positive cingulum rests
 Complete and three quarter crowns
 Pin retained inlays
 Reshape existing cingulum (primarily
maxillary cuspids)
 Light cured composite resin ?
 Long term survivability unclear
 Bonded rests ?
 Long term survivability unclear
Full veneer crown ¾ crown Reshaped cingulum Pin retained inlay

23. Crescent shaped
cingulum rests
Three quarter crowns

24. Anterior rests
Crescent shaped cingulum rests
Full veneer crowns

25. Anterior rests
Crescent shaped cingulum rests
Full veneer crowns

26. Anterior rests
Crescent shaped cingulum rests
Full veneer crowns

27. Circular Concave Rests
 Used when their insufficient space for a cingulum rest because of the
opposing occlusion
 Better tolerated by the tongue than crescent shaped cingulum rests
 May create greater leverage on the tooth compared to cingulum rests when
used improperly and must not be used on the edentulous side of the
extension base cases.
Extension
base

28. Circular Concave Rests
Problems with circular concave rests
 Difficult to prepare a positive rest without perforating the
enamel
 Difficult to position the rest in the center of the tooth
 Difficult to keep clean
 Difficult to obtain impressions and cast for positive and
engagement and contact by the RPD casting

29. Circular Concave Rests
 When preparing this type of rest on a virgin tooth often the
enamel is perforated and an amalgam restoration must be
placed (Circle)

30. Circular Concave Rests
 Completed RPD of a patients using circular concave
rests on the canines.

31. Anterior rests
Incisal Rests
 Used primarily on
mandibular canines
 Sometimes used to
engage mandibular
incisors to provide
stability when these teeth
are periodontally
compromised
Not as ideal as a cingulum rest
because of increased leverage

32. Anterior rests
Incisal Rests
 Used primarily for support and stability
 Can be used to restore anterior guidance when necessary
Not as ideal as a cingulum rest because of increased leverage

33. Anterior rests
Incisal Rests
 Inthis case (arrow), the incisal rest was also
used to restore the anterior
 Note how the rest extends onto the labial
surface

34. Anterior rests
Incisal Rests
Requirements
 It must extend over the incisal edge in order to engage the
abutment tooth in a positive manner
 It must extend 1/3-1/2 width of incisal edge with sufficient
clearance when necessary
 Concave rest seat mesiodistally
 Convex rest seat buccolingually

35. Anterior rests
Incisal Rests
 Rarely used for maxillary anterior teeth because of concerns
regarding esthetics and occlusal interference with the opposing
mandibular teeth
 Used when the mandibular anterior teeth are virgin and when
full veneer crowns are not an option
 Disadvantage: It may create greater leverage on the tooth
compared to cingulum rests and is only used when the lingual
anatomy of the tooth is not appropriate for preparation of a
cingulum rest

36. Posterior rests
Functions
 Provide rigid prosthetic support
 Direct occlusal forces along the long axis of the teeth
 Restore occlusion
 Splinting periodontally compromised teeth
 Provide reciprocation and stabilization (bracing)
 Extended occlusal rests

37. Posterior rests – Function
Functions
 Posterior rest must be definitive and positive in order to
direct occlusal forces along long axis of the teeth
Preservation of remaining teeth requires
that occlusal forces be directed along the
long axis of the abutments.

38. Posterior rests - Functions
Provide rigid prosthetic support
 Posterior rests should be rigid with sufficient bulk to resist flexure. If they
flex, eventually they will fracture
 In addition, if the rest flexes during function the angulation of occlusal
forces directed through the rest to the abutment teeth may change and
may overload the periodontium and lead to premature loss of the
abutment.

39. Posterior rests
 When possible extend posterior
rests into the center of the tooth
Photoelastic
analysis

40. Posterior rests
 This will direct the occlusal
forces along the long axis of
the teeth
Photoelastic model

41. Posterior rests
 When the rest is placed on a marginal ridge, the bone associated with the
distal root becomes overloaded
 When the rest extends into the center of the tooth the forces are more
equitably distributed in the alveolar bone.
Photoelastic model

42. Posterior rests
 Note that the center portion (arrow) is the deepest portion of the
rest and is contoured a half circle

43. Extension Based RPD’s
 Axis of rotation
(fulcrum line) is
determined by the
position of the
rests adjacent to
the edentulous
extension area.

44. Extension Based RPD’s
 In a posterior tooth the
rotation occurs through the
posterior portion of the rest.
 Therefore this portion of
rest should be contoured
as a half sphere.

45. Rest requirements
 Harmonize with existing occlusion and
no interference with occlusion.

46. Posterior rests – Other Functions
Restore occlusion
Rests are often extended
to cover two or more
posterior teeth to restore
the plane of occlusion and
occlusal harmony.
Examples
 Tipped teeth
 Teeth that have not fully
erupted
 Restoring the vertical
dimension of occlusion.

47. Posterior rests – Other Functions
Restore occlusion
Rests are often extended to
cover two or more posterior
teeth to restore the plane of
occlusion and occlusal
harmony.
Examples
 Tipped teeth
 Teeth that have not fully
erupted
 Restoring the vertical
dimension of occlusion
Note that the occlusal plane has been leveled with the RPD

48. Posterior rests - Functions
Help stabilize periodontally involved teeth
Continuous rest
When a multiple teeth are periodontally compromised teeth, tipped
and displaced a posterior continuous posterior rest can restore
and stabilize occlusion and prevent further migration of teeth.

49. Posterior rests - Functions
Stabilize periodontally involved teeth
Continuous rest (ribbon rest)
Retention for this Kennedy class IV RPD was obtained from the
lingual side. Reciprocation was obtained from the continuous rests
and the proximal plates.

50. Posterior rests - Functions
Stabilize periodontally involved teeth
These continuous rests and the proximal plates unite
the arch segments
When an occlusal force is applied in any region all the
remaining teeth act in unison to provide support.

51. Posterior rests – Functions
Stabilize periodontally involved teeth
Besides replacing the anterior teeth the continuous rests
and the proximal plates of the RPD framework unite the
arch segments.
When an occlusal force is applied in any region all the remaining
teeth act more in unison to provide stability and support

52. Posterior rests
Functions
 Provide reciprocation and
stabilization

53. Posterior rests
Embrasure rests
 Used to avoid interproximal food impaction
 Used to strengthen framework connection to the
rest
 Best results with surveyed crowns

54. Preparing posterior rests
 Adequate thickness and width through entire length of rest (I/
3 the width and 1.2-1.5 mm in thickness)
 The center is the deepest portion
 Attempt to keep within the enamel
 Harmonious with the opposing occlusion

55. Preparing posterior rests
 Adequate thickness and width through entire length of rest (I/
3 the width and 1.2-1.5 mm in thickness)
 The center is the deepest portion
 Attempt to keep within the enamel
 Harmonious with the opposing occlusion

56. Preparing posterior rests
 Adequate thickness and width through entire length of rest (I/
3 the width and 1.2-1.5 mm in thickness)
 The center is the deepest portion
 Attempt to keep within the enamel
 Harmonious with the opposing occlusion

57. Tooth Preparation for RPD’s

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