Retainers in RPD/ Labial orthodontics


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Retainers in RPD/ Labial orthodontics

  1. 1. Retainers in RPD INDIAN DENTAL ACADEMY Leader in continuing dental education
  2. 2.  Retention can be defined as that quality inherent in a prosthesis that resists the vertical forces of dislodgement. Or  It is the resistance to removal from vertical forces which tend to dislodge prosthesis away from its foundation.
  3. 3.  Retention for removable partial denture is achieved primarily by  Mechanical means (Direct & indirect retainers)  Harnessing the patient’s muscular control acting through polished surfaces of denture  Using inherent physical forces which arise from coverage of mucosa by the denture
  4. 4. Movement of partial denture Distal extension partial denture can move along three axis.  Rotation about an axis through the most posterior abutments,
  5. 5. Movement of partial denture  Rotation about a longitudinal axis as the distal extension base moves in a rotary direction about the residual ridge.
  6. 6. Movement of partial denture  Rotation about an imaginary vertical axis near the centre of the dental arch.
  7. 7. Retainers  Direct retainer  Intracoronal  Extracoronal  Indirect Retainer
  8. 8. Intracoronal retainers  Prefabricated  Provide retention by frictional resistance
  9. 9. Intracoronal retainers Advantage  Batter esthetics  Better vertical support trough a rest seat located more favorably in relation to horizontal axis of the abutment tooth  Horizontal stabilization is similar to that of an internal rest
  10. 10. Intracoronal retainers Disadvantages  Require prepared abutments and castings  Require somewhat complicated clinical and laboratory procedures  They eventually wear with resulting loss in retention  Difficult to repair and replace  Effective in proportion to their length and are therefore least effective on short teeth  Difficult to place completely within the circumference of an abutment tooth  More expensive
  11. 11. Extracoronal direct retainer  Prefabricated- Dalbo  Custom made- Clasp
  12. 12. Clasp retainer Component  Occlusal rest  Retentive arm  Reciprocal arm  Minor connector
  13. 13. Amount of retention  Size of angle of cervical convergence  How far clasp arm is place in cervical convergence  Flexibility of clasp arm  It’s length  It’s relative diameter  It’s cross-sectional form  Material of clasp arm
  14. 14.
  15. 15. Angle of cervical convergence  Area cervical to height of contour  Amount of convergence – relative to path of placement and removal  A definitive path of placement is possible- guiding planes.
  16. 16. How far clasp arm is place in cervical convergence  Relative uniformity of retention  Location of clasp arm in relation to angle of cervical convergence, not in relation to height of contour.
  17. 17. Flexibility of clasp arm  Length α Flexibility  Diameter 1/ α Flexibility
  18. 18. Flexibility of clasp arm  Cross sectional form  Half round form →Unidirectional  Round form →universal  Material of clasp: Wrought wire > cast gold > chrome alloys
  19. 19. Stabilizing- reciprocal cast clasp arm  It should be rigid  It should taper in one dimension only  It’s average diameter must be greater then retentive arm
  20. 20. REQUIREMENTS OF CLASP DESIGN  Retention  Stability  Support  Reciprocation  Encirclement  Passivity
  21. 21. Basic principles of clasp design  More than 180° of the greatest circumference of the crown of the tooth must be included  Continuous contact  Three widely separated area  Occusal rest must be designed  Each retentive terminal must oppose a reciprocal component.
  22. 22. Basic principles of clasp design  Positive guiding planes  Retentive clasps should be bilaterally opposed  Path of escapement of each retentive clasp must be other then parallel to path of removal of the prosthesis.
  23. 23. Basic principles of clasp design  Amount of retention should always be minimum necessary  Clasp retainer should not transmit off-vertical forces to the abutment tooth.  Reciprocal element →at the junction of gingival and middle thirds  Terminal end or retentive arm →Gingival third
  24. 24. Type of clasps  Circumferential clasp  Ring clasp  Embrasure clasp  Multiple clasp  Half- and –half clasp  Reverse action clasp  Bar clasp or RPI clasp
  25. 25. Circumferential clasp  This clasp consists of occlusal rest & a buccal and lingual arm originating from a common body
  26. 26. Circumferential clasp  Most logical clasp for tooth supported partial dentures because of excellent support, bracing and retentive qualities  Can be used in a wide variety of situations
  27. 27. Circumferential clasp Disadvantages  More tooth coverage  It’s occlusal approach may increase the width of occlusal surface of the tooth  More metal may be displayed than bar clasp  It’s half round form prevents to increase or decrease retention
  28. 28. Ring clasp  Encircles nearly all of a tooth from it’s point of origin  Indications: Tipped molars were a proximal undercut cannot be approached by any other means
  29. 29. Embrasure clasp  Essentially two simple circlet clasp joined at the body
  30. 30. Multiple clasp  Simply two opposing circumferential clasps joined at the terminal end of the two reciprocal arms
  31. 31. Half- and –half clasp  It consists of a circumferential retentive arm arising from one direction and reciprocal arm arising from another  The second arm must arise from a second minor connector and is with or without occlusal rest
  32. 32. Reverse-action clasp  When retentive undercut is adjacent to occusal rest  Bar clasp cannot be used because of soft tissue undercut  Ring clasp cannot be used due to lingual undercut
  33. 33. Bar clasp  The bar clasps approach the undercut or retentive area on the tooth from a gingival direction  Flexibility of bar clasp → taper and length of approach arm
  34. 34. Bar clasp DISADVANTAGES  Greater tendency to trap food debris  Does not contribute as much to bracing and stabilization as most circumferential clasps do
  35. 35. Bar clasp  Classified as  T. Modofied T,I, or Y
  36. 36. RPI system
  37. 37. RPI system Three approach for the application of RPI system
  38. 38. RPI system  Proximal plate contact 1mmgingival portion of GP
  39. 39. RPI system  RPA Clasp
  40. 40. Combination clasp  It is a circumferential clasp, but bar clasp may be used  wrought wire retentive clasp arm and a cast reciprocal clasp arm  If high heat chrome alloy is used, the wrought wire must be soldered to the completed framework
  41. 41. Combination clasp
  42. 42. How to select a clasp design  It’s flexibility  Stabilization for horizontal & rotational forces  Sufficient rigidity  Applicable to malposed or rotated tooth  Presence or absence of tissue undercut
  43. 43. How to select a clasp design  Clasp terminal is adjustable or not  Area to be covered by clasp  Effect on width of occlusal table  Can it be replaced.
  44. 44. Indirect Retainers  Restrict the movement of denture base away from basal seat, as it tend to rotate around one of the fulcurum line .  Rigid unit of partial denture framework, that are located on definite rest seats on the opposite side of fulcurum line from the distal extension base .  Theses component should be placed as far as possible from fulcurum line for best possible leverage.
  45. 45. Movement of partial denture
  46. 46. Fulcurum line  This is an imaginary line passing through teeth and component part of partial denture, around which denture rotates slightly when subjected to various forces directed towards or away from the residual ridges.
  47. 47. Indirect retainer - types  Auxiliary occlusal rest  Canine extension from occlusal rest  Canine rest  Linguoplate with rest on terminal ends  Modification areas.  Rugae support  The proximal plate
  48. 48. Factor influencing effectiveness of indirect retainer  Stable principal occlusal rests  Distance from the fulcrum line  Rigidity of the connectors supporting the indirect retainer  Effectiveness of the supporting tooth surface.
  49. 49. CONCLUSION  We can select any of the clasp designs but that should be based on sound biological & mechanical principles of clasp designs
  50. 50. THANK YOU For more details please visit