Partial denture rests provide support (resist the forces of occlusion), bracing, reciprocation and in some situations can be used to restore the occlusion.  Rests must engage the abutment teeth in a positive fashion and not permit the prosthesis to slide off the tooth or allow the abutments to move out of the existing relationships to other teeth as occlusal pressures is increased.  This program illustrates in detail the design of occlusal rests for anterior and posterior teeth.


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Partial Denture Rests — Course Transcript

  • 1. Partial Denture Rests John Beumer III and Ting Ling Chang Distinguished Professor Emeritus Division of Advanced Prosthodontics, Biomaterials and Hospital Dentistry This program of instruction is protected by copyright ©. No portion of this program of instruction may be reproduced, recorded or transferred by any means electronic, digital, photographic, mechanical etc., or by any information storage or retrieval system, without prior permission.
  • 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 Incisal rests (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. 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 Anterior rests
  • 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. Completed RPD of a patients using circular concave rests on the canines. Circular Concave Rests
  • 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 In this 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 Retention for this Kennedy class IV RPD was obtained from the lingual side. Reciprocation was obtained from the continuous rests and the proximal plates. Continuous rest (ribbon rest)
  • 50. Posterior rests – Functions Stabilize periodontally involved teeth When an occlusal force is applied in any region all the remaining teeth act in unison to provide support. These continuous rests and the proximal plates unite the arch segments
  • 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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