Direct retainers /certified fixed orthodontic courses by Indian dental academy


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The Indian Dental Academy is the Leader in continuing dental education , training dentists in all aspects of dentistry and offering a wide range of dental certified courses in different formats.

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Direct retainers /certified fixed orthodontic courses by Indian dental academy

  1. 1. DIRECT RETAINERS INDIAN DENTAL ACADEMY Leader in continuing dental education
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  3. 3. DIRECT RETAINERS  Introduction The removable partial denture must have sufficient retention to resist reasonable dislodging forces.  Primary Retention: for the removable partial denture is accomplished mechanically by elements on the abutment teeth. placing retaining  Secondary Retention: is provided by the intimate relationship of minor connector contact with the guiding planes, denture bases, and major connectors (maxillary) with underlying tissues.
  4. 4.  Definition: A direct retainer is any unit of removable dental prosthesis that engages an abutment tooth in such a manner as to resist displacement of the prosthesis away from basal seat tissues.  The two basic types of direct retainers: Intracoronal retainer Direct Retainers (precision attachment) Extracoronal (clasp ) Retainer
  5. 5.  Intracoronal Retainers: which is cast or attached totally within the restored natural contours of an abutment tooth. This type of retainer is composed of a prefabricated machined key and keyway, with opposing vertical parallel walls that serve to limit movement and resist removal of the partial denture through frictional resistance.  Extracoronal Retainers : which uses mechanical resistance to displacement by components placed on or attached to the external surfaces of an abutment tooth  Extracoronal D.R. Circumferential clasp
  6. 6.  Components of clasp Assembly 1. Rest – Provides support for prosthesis 2. Body – Connects rest and clasp arms to minor connector 3. Reciprocal arm – must be rigid above the height of contour 4. Retentive arm – Provides direct retention below the height of the contour 5. Shoulder 6. Approach arm 7. Terminal
  7. 7. a. The occlusal rest b. The body c. The shoulders d. The terminals e. The clasp arms f. The strut g. the approach arm h. the terminal
  8. 8.  Clasps can be classified on the basis of construction 1. Cast clasp 2. Wrought wire clasp 3. Combination clasp  Clasps classified on a basis of design 1. Circumferential clasp (Akers – suprabulge) 2. Bar clasp (vertical projection – Roach infrabulge)
  9. 9. Circumferential clasp: It approaches the undercut from occlusal direction – “pull” type of retention
  10. 10. Bar clasp: Retentive terminal approaches the undercut from gingival direction – below the surveyline – “push” type of retention.
  11. 11. a. Circumferential clasp b. Bar clasp
  12. 12. ATTRIBUTES OF PROPERLY DESIGNED CLASP  The clasp should possess the attributes of  Retention  Stabilization  Support  Encirclement  Reciprocity  Passivity
  13. 13. RETENTION  Retention is the property which enables the clasp to resist dislodgement from the tooth in an occlusal direction. A dislodging force may be activated by speech, muscle action, mastication, deglutition, sticky foods, or gravity.
  14. 14. Retentive arm of the clasp
  15. 15.  The length of the clasp arm. The greater the length, the greater the resiliency.  The diameter of the retentive arm. The smaller the diameter, greater the resiliency.  The cross sectional form. A round clasp arm is more resilient than one that is half round or oval in shape.  The taper. Proper taper can increase flexibility as much as fourfold. The retentive arm of the clasp should taper evenly and uniformly from its origin at the body of the clasp to its terminal extremity.
  16. 16.  The kind of alloy. The chromium Cobalt alloys have a higher modulus of elasticity, hence are not resilient as gold alloys of the same diameter. as  The type of alloy. An alloy is wrought form is more resilient than the same alloy of identical diameter in cast form, because of its internal structure.  Heat treatment of the alloy. Proper heat treatment, gold in particular, will increase the resilience substantially, whereas improper heat treatment may render it brittle and with no resilience whatever.
  17. 17. Flex in horizontal plane Flex in all planes Cast Clasp Wrought clasp
  18. 18. Uniform taper in thickness and necessary both width Clasp terminal should half as thick as origin Flexibility of a clasp arm increases as length of clasp increases be
  19. 19. STABILIZATION  Stabilization, or bracing is the resistance which the clasp contributes to displacement of the prosthesis in horizontal plane . All of the clasp components, with the exception of the retentive terminal, contribute this property in varying degrees.
  20. 20. SUPPORT  Support is the property of the clasp which enables it to resist displacement in a gingival direction. The occlusal rest is the prime support unit of the clasp, although the body and the shoulder of the clasp, positioned as they are above the greatest diameter of the tooth, also contribute a substantial amount of support.
  21. 21. ENCIRCLEMENT  The clasp should be so designed that it encircles at least 180 degrees of the crown of the tooth, to preclude movement of the tooth out of the clasp arms as strmsses are applied.
  22. 22. Each clasp assembly must encircles more than 180 0 A clasp that fails to produce encirclement will act as orthodontic appliance
  23. 23. RECIPROCITY • Reciprocation may defined as “ the means by which one part of the appliance is made to counter the effect created by another part”. • Reciprocation is needed most when the retentive terminal flexes over the bulge of the crown during insertion and removal of the prosthesis.
  24. 24. Reciprocal arm of the clasp is rigid .
  25. 25. PASSIVITY  When the clasp is in place on the tooth, it should be passive. Passivity is an important requirement of a properly designed clasp. A clasp so designed will permit a slight degree of movement of the base without transmitting any appreciable amount of the stress to the abutment tooth.
  26. 26. A clasp must be completely seated to be passive
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  29. 29. SIMPLE CIRCLET CLASP  This is the most widely used clasp  It is the clasp of choice on tooth supported removal partial dentures  This clasp approaches the undercut on the abutment tooth from the edentulous areas and engages the undercut from the edentulous space.
  32. 32. SIMPLE CIRCLET CLASP Advantages: • The clasp fulfills the requirement of support, stability reciprocation, encirclement & passivity better than any other type of clasp. • It is easy to construct. • It is simple to repair.
  33. 33. SIMPLE CIRCLET CLASP Disadvantages: • It tends to increase the circumference of the crown. • In anterior part of the mouth is not acceptable. • It covers more tooth surface then the bar clasp and prone to caries. • Retentive undercuts on some teeth are difficult to reach with retentive terminal of the clasp
  34. 34. REVERSE CIRCLET CLASP Reverse circlet clasp is used when the retentive undercut is located on the surface of the abutment tooth adjacent to the edentulous space. In distal extension edentulous ridge partial denture the reverse approach clasp helps to control the stresses transmitted to the terminal abutment tooth on the edentulous side.
  36. 36. MULTIPLE CIRCLET CLASP It is opposing simple circlet clasps joined at the terminal end of the 2 reciprocal arms. It is indicated in periodontally weakened teeth. This is the form of splinting weakened teeth by a removable partial denture.
  37. 37. EMBRASURE CLASP ( MODIFIED Crib Clasp) The embrassure clasp is 2 simple circlet clasps joined at the body. It is most frequently used on the side of the arch where there is no edentulous space. Occlusal rest preparations must be made on both teeth and tooth structure must be removed from the buccal inclines of both teeth to provide space for adequate thickness of metal.
  40. 40. RING CLASP Indicated on tipped molars. Ring clasp engages the undercut by encircling the entire tooth from its point of origin. On mandibular molar the clasp encircles the tooth beginning on the mesiobuccal surface and eliminating in an infrabulge area on the mesiolingual surface. On a maxillary molar the direct of the clasp is reversed.
  41. 41. RING CLASP
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  43. 43. The entire clasp must be placed above the left of the contours except retentive tip. It must be designed with additional support in the form of an auxillary bracing arm. An additional occlusal rest on the opposite side of the tooth from the clasp origin provide additional support and proved further movement of the mesially inclined tooth.
  44. 44. C clasp Fishhook, or Hairpin Clasp The C clasp is a simple circlet clasp in which the retentive arm crosses the facial surface of the tooth from its point of origin, loops back in hairpin turn to engage a proximal undercut below its point of origin. The upper part of retentive arm must be rigid, the lower apart of the retentive arm should be tapered. It is the only flexible part of the clasp arm. The crown of the abutment tooth must have sufficient occlusogingival height to accommodate this double width of the clasp arm. The upper and lower arms of the retentive clasp must be designed such that food debris will not be retained.
  45. 45. C Clasp, Hairpin Clasp, Fishhook
  46. 46. Indications:  When the retentive clasp must engage an undercut adjacent to the occlusal rest or edentulous space and a soft tissue undercut precludes the use of of a bar clasp  The C Clasp is indicated when the reverse circlet clasp cannot be used because of lack of occlusal space.
  47. 47. Disadvantages:  The clasp covers a considerable amount of tooth structure, which may trap food debris.  It is not good choice for a young patient or one who is prone to caries, unacceptable esthetically, premolar teeth. and it is often particularly on
  48. 48. ONLAY CLASP  The onlay clasp is an extended occlusal rest with buccal and lingual clasp arms.  The clasp may originate from any point on the onlay that will not create occlusal interferences.  This clasp is generally indicated when the occlusal surface of the abutment tooth is below the occlusal plane, usually as a result of the tooth being tipped or rotated.  The onlay is used to restore the normal occlusal
  49. 49. Onlay clasp
  50. 50. COMBINATION CLASP The combination clasp consists of a Wrought wire retentive clasp arm and a cast reciprocal clasp arm. The cast reciprocal arm is normally a circumferential clasp. But a bar clasp may be used. The Wrought wire retentive arm is a circumferential clasp arm. It is used when maximum flexibility is required. Esthetics advantage because Wrought structure in smaller diameter than the cast clasp.
  52. 52. Advantages:  Flexibility.  Adjustability.  Appearance of the Wrought wire retentive arm.  Minimum of tooth surface covered.
  53. 53. Disadvantages:  It involves extra steps in fabrication.  It may be distorted by patient.  It may be less accurately adapted.
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  55. 55. Bar or Vertical Project Clasp Bar clasps approach the undercut from a gingival direction. It is more effective than the “pull” characteristic of circumferential clasps. retention Patient in contouring less difficulty inserting and more difficulty in removing removable partial denture with bar clasp than with circumferential clasp. Flexibility of the bar clasp can be controlled by the taper and length of the approach arm. Because of the gingival approach of the bar clasp it is usually esthetics than a circumferential clasp.
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  57. 57. DISADVANTAGES Greater binding to collect and hold food debris Because retentive of the arm increased it does flexibility not stabilization. of contribute the to
  58. 58. T - BAR CLASP T Bar clasp is frequently used on distal extension ridge where the usual undercut .
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  60. 60. I-bar clasp  Used on distobuccal surface of maxillary canines for esthetic reasons.  Retentive tip is in contact with abutment teeth.  I bar is a component of a partial denture referred to as RPI concept.
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  63. 63. Y- BAR CLASP  Y-Bar is basically a T-clasp its configuration occurs where the it is contour on the facial surface of the abutment tooth is high on the medial and distal angles.
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  65. 65. Leader in continuing dental education