1. Rests & Rest Seats

2. Rest
Rigid component resting in a recessed preparation on the occlusal, lingual or incisal surface
Provides vertical support

3. Rest Seat
Portion of a tooth prepared to receive a rest

4. Functions
SUPPORT - prevents denture base from moving cervically & impinging gingiva
Slides down incline
Fractured abutment, no rest seat

5. Major connector imbeds into tissue

7. Functions
Direct forces along long axis of abutment

8. Functions
Maintain a clasp -tooth relationship

9. Functions Prevent extrusion of abutments
Provide reference for relines or impressions

10. Functions Act as indirect retainer
Prevents rotation (Class I or II RPD’s only)

11. Preparation of Rest Seats
Light pressure
High-speed handpiece
+/- Waterspray
Minimal heat is generated

12. Preparation of Rest Seats
Keep in enamel
No anesthesia

13. Preparation of Rest Seats
Occlusal Rest Seats
Diamonds

14. Rest Seat Form
Smooth flowing outline form (no sharp angles)

15. Occlusal Rest Seat Form
Rounded triangular shape
Apex near center of tooth

16. Occlusal Rest Seat Form
Base of triangle should be one third the bucco-lingual width of the tooth

17. Occlusal Rest Seat Form
Marginal ridge must be lowered and rounded 1-1.5mm
Bulk of metal to prevent fracture

18. Occlusal Rest Seat Form
Begin preparation middle of marginal ridge,1-1.5mm
Depth gauge is single width of bur, mm deep from marginal ridge on either side of bur

19. Occlusal Rest Seat Form
If plan to refine external line angle reduce 1mm
Refinement and rounding will deepen
Minimizes chance of excessive depth

20. Occlusal Rest Seat Form
After depth gauge preparation widen bucco-lingually
1/3 occlusal width at proximal surface

21. Avoid Undercuts All axial walls must draw
Round burs are good for depth cuts, but leave undercuts unless the operator pulls the bur away from the tooth at widest part of the preparation

22. Avoid Undercuts
Mushroom shaped burs leave slightly divergent walls which minimizes chance of undercuts

23. Must Draw with Path of Insertion
Rest is rigid and framework will not seat if rest seat preparation is undercut with path of insertion
Axial walls draw with each other and also with the path of insertion
Axial walls do NOT draw with each other NOR with the path of insertion
Axial walls draw with each other and with the long axis of the tooth but NOT with the path of insertion

24. Occlusal Rest Seat Form
Floor inclined towards the center
Angle formed by rest and minor connector should be less than 900

25. Occlusal Rest Seat Form
Deepest portion is central

26. Occlusal Rest Seat Form
Floor should be concave or spoon shaped ball-&-socket joint
Minimizes horizontal stresses & torque

27. Occlusal Rest Seat Form
Directs occlusal forces along long axis
Minimizes orthodontic movement

28. “Positive” Rest Seats
Explorer will not slide off rest seat

29. Occlusal Rest Seat Video

30. Occlusal Rest Seat Form
Conventional Form

31. Occlusal Rest Seat Form
Adjacent Tooth
Preparation does not involve proximal contact for facial line angle
Lingual flared more - space for minor connector

32. Double Embrasure Rest Seat Form
Adjacent teeth, the form is also modified
Flared more on facial & lingual line angles

33. Double Embrasure Rest Seat Form
Provides space for the retentive & bracing arms
Ensure all line angles are smoothed

34. Lingual Rest Seats Usually the canine, due to well-developed cingulum
When canine can not be used, incisor may be used

35. Cingulum Rest Seat Form
Inverted “V”
< 900

36. Cingulum Rest Seat Form
Slightly rounded to avoid sharp line angles
Test as ‘positive’ with explorer tip
1mm depth, 1.5 mm clearance

37. Correct Preparation

38. Correct Preparation

39. Preparation Too High

40. Preparation Too Low

41. Preparation of Rest Seats
8837K-014
Cingulum Rest Seats & Guiding Planes
Long, medium diameter cylindrical diamond 8837K-014

42. Cingulum Rest Preparation
Do not create an enamel undercut
Cylindrical bur from incisal approach

43. Cingulum Rest Preparation
Ensure middle of preparation is full 1-1.5mm
Bring bur past midline to ensure middle of rest seat is sufficiently repaired

44. Cingulum Rest Seat Video

45. Cingulum Rest Seat Placement
Place in sound tooth structure or restorations
Not on amalgam restorations
If not prominent or large pulp
Use different tooth
Bonded rest seat
Onlay or crown

46. Maxillary Cingulum Rest Seats
Avoid opposing occlusion
Minimum of 1.5mm clearance in centric and excurions

47. Maxillary Cingulum Rest Seats
1.5 mm minimum clearance for metal
Check with articulated models when possible

48. Bonded Cingulum Rests Flat emergence profile
Pumice, rinse, etch, bond using rubber dam
Ensure cervical composite well adapted

49. Composite Bonded Rest Seat Form
Correct
Overcontoured
Overcontoured
Open margin

50. Bonded Rest Seat Video

51. Round Lingual Rest Seat Form
Mesial of the canine teeth when typical cingulum rest contraindicated:
Lack of clearance with the opposing teeth
Poor cingulum
Large restoration

52. Round Lingual Rest Seat Form
Spoon shaped, similar to occlusal rest seat
More difficult due to incline of lingual surface
Easily incorporated into crowns

53. Incisal Rests Inferior mechanically & esthetically
Lingual rest is nearer to the center of rotation
Less torquing potential

54. Bring to Seminar Rooms:
Ball burnisher if you have one
Box of casts with preparations on them
Any typodonts for checking of guiding plane preparations (Surveyor needed for checking)