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Rests & Rest Seats

Rests & Rest Seats. Rest. A rigid component resting in a recessed preparation on the occlusal, lingual or incisal surface Provides vertical support. Rest Seat. Portion of a tooth prepared to receive a rest. Functions. Direct forces along long axis of abutment. Slides down incline.

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Rests & Rest Seats

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  1. Rests & Rest Seats

  2. Rest • A 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 • Direct forces along long axis of abutment

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

  6. Major connector imbeds into tissue

  7. Functions • Maintain a clasp -tooth relationship

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

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

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

  11. Preparation of Rest Seats • Keep in enamel • No anesthesia

  12. Preparation of Rest Seats • Occlusal Rest Seats • Diamonds • 8801- 014 • 38006 -135 8801- 014

  13. Rest Seat Form • Smooth flowing outline form (i.e. no sharp line angles)

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

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

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

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

  18. Occlusal Rest Seat Form • Deepest portion is central

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

  20. Occlusal Rest Seat Form • Directs the occlusal forces along the long axis of the tooth • Prevent orthodontic movement

  21. “Positive” Rest Seats • Explorer tip will not slide off the rest seat

  22. Avoid Undercuts • Must draw along path of insertion

  23. Occlusal Rest Seat Movie

  24. Occlusal Rest Seat Form • Conventional Form

  25. Occlusal Rest Seat Form • Adjacent Tooth • Rest not flared to facial line angle • Lingual flared more - space for minor connector

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

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

  28. Lingual Rest Seats • Usually the canine, due to its well-developed cingulum • When canine is not available, an incisor may be used

  29. Cingulum Rest Seat Form • Inverted “V” • < 900

  30. Cingulum Rest Seat Form • Slightly rounded to avoid sharp line angles • Test as ‘positive’ with explorer tip • 1mm depth

  31. Correct Preparation

  32. Preparation Too High

  33. Preparation Too Low

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

  35. Cingulum Rest Preparation • Do not create an enamel undercut • Cylindrical bur along the long axis of the tooth

  36. Cingulum Rest Seat Movie

  37. 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

  38. Maxillary Cingulum Rest Seats • Avoid opposing occlusion

  39. Maxillary Cingulum Rest Seats • 1.5 - 2.0 mm clearance for metal • Check with articulated models

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

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

  42. Bonded Rest Seat Movie

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

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

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

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

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