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Direct & indirect retainers in rpd

the science,principles and requirements of direct and indirect retainers in removable partial dentures.

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Direct & indirect retainers in rpd

  1. 1. Direct and indirect retainers Vinay Pavan Kumar .K 2nd year P G student Dept of Prosthodontics AECS Maaruti College of Dental Sciences
  2. 2. Direct retainers Indirect retainers Definition Classification Principles of design Extracoronal retainers Types Definition Factors affecting types of indirect Requirements retainers
  3. 3. Direct retainer: It is that component of a removable partial denture that is used to retain and prevent dislodgment, consisting of a clasp assembly or a precision attachment (GPT 8)
  4. 4. Direct retainers Intracoronal Extracoronal Precision Semi-precision Extracoronal Clasps Attachment
  5. 5. Intracoronal retainers In 1906 the principle of the internal attachment was first formulated by Dr. Herman E.S. Chayes
  6. 6. Extracoronal Retainers  Prothero provided a Conceptual Basis for mechanical retention
  7. 7.  Clasps mainly divided 2 types  Occlusally approaching which approach the undercut from the occlusal area and gingivally approaching which enter the undercut crossing the gingival margin.
  8. 8. Clasp Assembly The part of a removable dental prosthesis that acts as a direct retainer and/or stabilizer for a prosthesis by partially encompassing or contacting an abutment tooth. Components of the clasp assembly include the clasp, the reciprocal element, the cingulum, incisal or occlusal rest, and the minor connector.
  9. 9. Parts of clasp assembly Circumferential Clasp (Retentive Arm) Reciprocating (Bracing) Arm Distal Occlusal Rest Seat Proximal Plate
  10. 10. Principles of Clasp Design 1. Encirclement- more than 180 degrees in greatest circumference if the tooth engaged by the clasp assembly 2. Occlusal rest - to prevent the movement of the clasp arms cervically. 3. Each retentive terminal should be opposed by a reciprocal component
  11. 11. 4. Clasp retainers on abutment teeth adjacent to distal extension bases should be designed to avoid direct transmission of forces to the abutment 5.The amount of retention should always be the minimum necessary to resist reasonable dislodging forces. 6. Reciprocal elements – junction of gingival and middle third Terminal retentive arm – gingival third
  12. 12. Functional requirements of the clasp Retention Support Stability Reciprocation Encirclement Passivity
  13. 13. Retention  Is obtained by the incorporation of a flexible element of the clasp into the undercut.  Sufficient undercut to be engaged to obtain desired retention.  Force from the clasp arm on flexing must be within the tolerance of the PDL and must be less to prevent deformation of the clasp arm itself.
  14. 14. Factors affecting retention ◦ Tooth factors: Size of the angle of cervical convergence ◦ How far the clasp terminal is placed into the angle of cervical convergence
  15. 15. Clasp arm flexibility  Material used: cast chrome (0.010”) cast gold (0.015”) wrought alloy (0.020”)
  16. 16.  Length of the clasp •The longer the clasp arm the more flexible. • Flexibility is directly proportional to the cube of its length. •By increasing the length, the horizontal stresses imparted to the abutment during placing and removal is reduced
  17. 17.  Cross section: round > half round  Modulus of elasticity: more the modulus - less flexibility  Diameter of clasp: flexure inversely proportional to the diameter.  Alloy: wrought > cast
  18. 18. Support  Support is the quality of the clasp assembly to resist displacement of the prosthesis in the apical direction.  a rest must contact the surface of the abutment tooth at a properly prepared surface- rest seat
  19. 19.  A properly prepared rest will prevent the tissueward movement of the prosthesis.  maintains the position of the clasp assembly in relation to the abutment.  Transmits forces along the long axis of the abutments
  20. 20. Stability  Resistance to horizontal displacement
  21. 21. Reciprocation  Counteracts lateral displacement of an abutment when retentive clasp terminus passes over the height of contour
  22. 22. Encirclement  Prevent movement of abutment away from associated clasp assembly  More than 180 degrees
  23. 23. Passivity  Prevent the transmission of the adverse forces to the associated abutment  Be passive until a dislodging force is applied
  24. 24. Classification of extra-coronal retainers  Supra bulge clasps (occlusally approaching, circumferential clasps)  Infrabulge clasps (gingivally approaching, projection or bar clasps)  Combination clasps
  25. 25. Circumferential clasps  The cast circumferential clasp design was introduced by Dr N B Nesbitt in 1916.  Simple, easy to construct- excellent support, bracing, retentive properties.  Close adaptation to tooth therefore minimises food entrapment  Disadvantage- covers large amount of tooth surface
  26. 26.  Circlet clasp.  Reverse circlet  Multiple circlet clasp  Embrasure clasp.  Reverse action or hair pin clasp  Ring clasp.  Back action and reverse back action clasp
  27. 27. Simple Circlet clasp  Tooth support RPD  Undercut remote from edentulous area  Half round  Disadvantages - Increase tooth coverage - compromised esthetics
  28. 28. Variations of circlet clasp  Back action clasp  Reverse back action  Ring clasp  C clasp or hair-pin clasp
  29. 29. Reverse circlet clasp  Undercut located adjacent to edentulous area  Kennedy class I ,II  Disadvantages - Lack of rest adjacent to edentulous area - Poor esthetics
  30. 30. Multiple circlet design  2 simple circlet clasp joined at the terminal aspect of their reciprocal elements  Principle abutment is periodontal compromised and the forces are distributed between multiple abutment teeth
  31. 31. Embrasure clasp  2 simple circlet joined at bodies  Used on side of the arch where there is no edentulous space  Can be used only when adequate tooth preparation is possible
  32. 32. C-clasp design  Fish hook” or “Hairpin” clasp  Simple circlet clasp with loop back retentive arm  Sufficient crown height  Disadvantages - Insufficient flexibility - Tooth coverage - Esthetics compromised
  33. 33. Combination clasp  Cast metal reciprocal arm and wrought wire retentive arm  abutment adjacent to Kennedy class I and II area Advantage • kinder to the tooth can engage greater undercut Disadvantage • more prone to breakage than cast • minimal stabilizing
  34. 34. Gingivally approaching clasps /Bar/Roach type Approach the undercut gingivally and have a push type of retention.
  35. 35. Approach arm • It is a minor connector that connect the retentive tip to the denture base. • It crosses the gingival margin at right angle and it is the only flexible minor connector. • Flexibility of the clasp is controlled by the taper and length of the approach arm • More esthetic
  36. 36. Retentive terminal • It should end on the surface of the tooth below the undercut.
  37. 37. T-clasp  Kennedy class I and II  Undercut locate adjacent edentulous area  Contraindication - Severe soft tissue undercut - Height of contour locate near occlusal surface
  38. 38. Modified T-clasp  No retentive horizontal projection  Kennedy class I and II  Undercut locate near adjacent edentulous area  Canine and premolar  Advantage - esthetics
  39. 39. Y-clasp  Equivalent to T-clasp  Approach arm terminates in the cervical third  Mesial and distal projection terminate near occlusal surface
  40. 40. I bar  Kennedy class I and II  RPI - Mesial rest - Proximal plate - I bar
  41. 41. Flexible clasps
  42. 42. • Acetal resin clasps are esthetic and are available in sixteen different shades. • To evaluate the effect of cast Co-Cr and acetal resin clasp on the surface of tooth. • The retentive force of cast Co-Cr clasp showed a decrease from 12.4 N to 8.1 N. • The retentive force of acetal resin clasp, reduced from 5.2 N to 4.03 N at the completion of experiment. • Acetal resin clasps do not abrade the surface of tooth and maintain retention A comparative study on Co-Cr and Acetal resin clasps; Pal .H etal TPDI • January 2014, Vol. 5, No. 1 pg 9- 13
  43. 43. Implants as direct retainers • Eliminates a visible clasp • placement of an implant within a modification space to the advantage of retentive needs requires consideration of anterior, mid, or distal placement • retainers utilizing teeth have always been restricted to tooth locations at either end of a span
  44. 44. Indirect retainer  Resists rotational displacement of an extension base from the supporting tissue  Kennedy class I, II and IV
  45. 45. Factors determining indirect retainer  Occlusal rests must be held in rest seats by direct retainer  Distance from fulcrum line  Placed on definite rest seat to prevent slippage  Rigidity
  46. 46. Auxiliary functions  Reduce A-P tilting of abutments  Stabilization – auxiliary guide planes  Anterior teeth stabilized  Auxiliary rest – stress distribution  Visual indication for reline
  47. 47. Forms of indirect retainer  Auxiliary occlusal rest  Canine extension from occlusal rest  Continuous bar retainer & lingual plate  Rugae Support
  48. 48. Auxiliary Occlusal Rest
  49. 49. Canine rest
  50. 50. Rugae Support
  51. 51. Major connectors - cingulum bars and linguo plates
  52. 52. References  Carr AB, Mc Givney GP, Brown DT, McCracken’s Removable Partial Prosthodontics, 12th edition , Canada, Elsevier Publishers, 2005 , pp:68-102  Stewart, Phoenix, Cagna, De Freest, Clinical Removable Partial Prosthodontics, 3rd edition, 2001, USA, Quintessence publishers, pp:53-96  Grant AA, Johnson W, An Introduction to Removable Denture Prosthetics, 1st edition, USA, Churchill livingstone, 1983, pp: 96-101
  53. 53.  Davenport JC , Basker RM, Heath JR, Ralph JP, Glantz PO, Retention ,Brit Dent J 2000;189(12):646- 657  Davenport JC , Basker RM, Heath JR, Ralph JP, Glantz PO, Hammond P, Bracing and reciprocation ,Brit Dent J 2001;190(1):10-14  Davenport JC , Basker RM, Heath JR, Ralph JP, Glantz PO, Hammond P, Clasp design , Brit Dent J 2001;190(2):71-81  Davenport JC , Basker RM, Heath JR, Ralph JP, Glantz PO, Hammond P, Indirect Retention ,Brit DentJ 2001;190(2):128-132

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the science,principles and requirements of direct and indirect retainers in removable partial dentures.


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