Dental Clasp designs 1 /certified fixed orthodontic courses by Indian dental academy


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Dental Clasp designs 1 /certified fixed orthodontic courses by Indian dental academy

  2. 2. INDIAN DENTAL ACADEMY Leader in continuing dental education
  3. 3. A removable partial denture must have Support  Stabilization  Retention 
  4. 4. RETENTION FOR RPD  Is derived mechanically by placing the retaining elements on the abutment tooth.
  5. 5. Direct retainer  Is that component of removable partial denture used to retain and prevent dislodgement , consisting of clasp assembly or precision attachment. -GPT.
  6. 6.  Two types of direct retainers : 1) Intra coronal retainer (Attachments). 2) Extra coronal retainer (clasps).
  7. 7. Intra coronal retainer
  8. 8. Extra coronal retainer.  Two configurations are 1) Manufactured retainers (Dalbo) 2) Custom-made retainers: a) Occlusally approaching (Circumferential or Akers clasp) b) Gingivally approaching (Bar or Roach clasp)
  9. 9.  Principle of extra coronal direct retainer. Resistance of the metal to the deformation.
  10. 10. Clasp   Is the component of the clasp assembly that engages a portion of the tooth surface and either enters an undercut for retention or remains entirely above the height of contour to act as a reciprocating element. Generally, it is used to stabilize and retain a removable prosthesis. -GPT.
  11. 11. Clasp assembly.  The part of a removable partial denture that acts as a direct retainer and or stabilizer for a prosthesis by partially encompassing or contacting an abutment tooth. -GPT.
  12. 12. Component parts. Rest Function Location Support Occlusal, Lingual, Incisal Minor connector Stabilization Clasp arms Stabilization Proximal surfaces extending from the prepared marginal ridge to the junction of the middle and gingival third of abutment crown. Apical portion of middle third of crown. Reciprocation Retention Apical portion of middle third of crown Gingival third of crown in
  13. 13.  The critical areas of an abutment that is responsible for retention, stabilization, reciprocation and guide planes can only be identified with the use of dental surveyors.
  14. 14.  General considerations: A clasp should be located at the undercut area in relation to the determined path of insertion and removal of the prosthesis.
  15. 15. Prothero’s cone theory. According to him , the tooth is considered as a pair of cones sharing a common base A clasp arm or tip that ends on a cervical cone would resist movement in the occlusal direction because to release from the tooth it would be forced to undergo deformation.
  16. 16.   The line which the two converging cones meet is called the height of contour, the term first coined by Kennedy. Devan referred to the surface of a tooth that is occlusal to the height of contour as supra bulge, and the tooth surface that is cervical to its height of contour as infra bulge.
  17. 17. Component parts of a clasp.   The component parts of a clasp assembly may be rigid or flexible. The flexible components are designed below the height of contour
  18. 18. Component parts of a clasp        Retentive clasp arm Retentive terminal Reciprocal arm Occlusal rest Shoulder Body Minor connector
  19. 19. Retentive arm A flexible segment of a removable partial denture which engages a under cut on an abutment which is designed to retain the denture – GPT Retentive arm retentive clasp arm + retentive terminal 
  20. 20. Retentive arm  Retentive clasp arm - not flexible - located above the height of contour Retentive terminal - flexible - located below the height of contour
  21. 21. Reciprocal arm A component of a clasp assembly specifically designed to provide reciprocation by engaging a reciprocal guiding plane and it counteracts the action of the clasp during the removal and insertion of the partial denture - GPT
  22. 22. Reciprocal arm   Location - on the side of the tooth opposite to the retentive arm always placed in the supra bulge area
  23. 23. Reciprocal arm   Function - resists the lateral forces exerted by the retentive arm when it passes through the height of contour - acts as an indirect retainer when placed on an abutment located anterior to the fulcrum line
  24. 24. Shoulder    Part of the clasp that connects the body to the clasp terminal Lies above the height of contour Provides stabilization against horizontal displacement
  25. 25. Body     Part of the clasp that connects the rests and shoulders of the clasp of the minor connectors. It is rigid and lies above the height of contour It contacts the guide plane of the abutment during the insertion and removal Part of the body that contacts the guiding plane proximal plate
  26. 26. rest    A rigid extension of a removable partial denture which contacts a remaining tooth or teeth to dissipate vertical or horizontal forces part of the clasp assembly that lies on the occlusal or lingual or incisal edge or surfaces of the teeth Resist tissue ward movement of the clasp by acting like a vertical stop
  27. 27. Minor connector   It joins the clasp with the remaining part of the framework In gingivally approaching clasp – Approach arm
  28. 28. BASIC PRINCIPLES OF CLASP DESIGN    Any clasp assembly must satisfy the basic prin­ciple of clasp design, is ENCIRCLEMENT which is that more than 180 degrees of the greatest circumference of the crown of the tooth passing from diverging axial surfaces to converging axial surfaces
  29. 29.    In the form of continuous contact when circumferential clasp arms are used. When bar clasp arms are used, at least three areas of tooth contact must be embracing more than one half of tooth circum­ference These are the occlusal rest the retentive terminal area, and the reciprocal terminal area.
  30. 30. Other principles to be considered in the design of a clasp are as follows:    1. The occlusal rest must be designed so that movement of the clasp arms cervically is prevented. 2. Each retentive terminal should be opposed by a reciprocal arm or element capable of resisting any orthodontic pressures exerted by the retentive arm. Reciprocal and stabilizing elements must be rigidly connected bilaterally
  31. 31.     3. Retentive clasps should be bilaterally opposed, that is, buccal retention on one side of the arch should be opposed by buccal retention on the other, or lingual on one side opposed by lingual on the other. In Class II situations the third abutment may have either buccal or lingual retention. In Class III situations, retention may be either bilaterally or diametrically opposed
  32. 32. . A, Retentive clasps should be bilaterally opposed. B, In Class II situations the retention on the third abutment may be on the buccal or the lingual . C, In Class III situations retention may be either (a) bilateral or (b) diametrically opposed.
  33. 33.    4. The path of escapement of each retentive clasp terminal should never coincide with the path of removal 5. Amount of retention should be the minimum, necessary to resist reasonable dislodging forces. 6. Clasp retainers on abutment teeth adjacent to distal extension bases should be designed so that, it should never exert tipping forces on the abutment teeth.
  34. 34.   7. Reciprocal elements of the clasp assembly should be located at the junction of the gingival and middle thirds of the crowns of abutment teeth. The terminal end of the retentive arm is optimally placed in the gingival third of the crown
  35. 35. Functional requirements of a clasp.       Retention Stability Support Reciprocation Encirclement Passivity.
  36. 36. Retention.    The function of retentive clasp arm is to provide retention. The retentive clasp is divided into three parts. The terminal third – engages the undercut area. Middle third - engages a minimal amount of undercut.
  37. 37.  The proximal third - is positioned above or shoulder the height of contour.
  38. 38. Three dimensions of a retentive undercut.
  39. 39. The following factors determine the amount retention a clasp is capable of generating.    1) Size of angle of cervical convergence. 2) How far into the angle of cervical convergence the clasp terminal is placed. 3) Flexibility of the clasp arm, which is the product of a) Its length which is directly proportional to the flexibility.
  40. 40.   b) Its diameter is inversely proportional to the flexibility of the clasp arm. c) Its cross-sectional form or shape, that is, whether it is round, half-round, or some other form. round clasp - flex in all spatial planes. half-round clasp-flex only in a single plane.
  41. 41. d) The material of which the clasp is made, that is whether it is made of a gold alloy, or chrome alloy. Chrome alloy have a higher modulus of elasticity and is less flexible.
  42. 42. A smaller cross sectional form of the clasp and less depth of the retentive undercut is engaged when chrome alloy is used and vice versa while using gold alloy.
  43. 43. Cast vs. wrought alloy.
  44. 44. Support.   Is the property of a clasp that resists displacement of the clasp in a gingival direction. The support units of a clasp are occlusal, lingual, or incisal rests.
  45. 45. Stability.   All clasp components except the retentive clasp terminals contribute to this property in varying degrees. Cast circumferential –offers greatest clasp amount of stability.
  46. 46. Reciprocation.  Each retentive clasp terminal must be opposed by a reciprocal clasp arm or another element of the partial denture capable of resisting horizontal forces exerted on the tooth by the retentive arm.
  47. 47. Reciprocation.    The reciprocal arm of the clasp is positioned on the opposite side of the tooth from the retentive arm. It also stabilizes the denture against horizontal movement. It should be placed preferably at the junction of the gingival and middle thirds of the abutment tooth (always positioned above the height of contour.)
  48. 48. Reciprocation.     It should contact the abutment tooth along with or before the retentive arm during insertion or removal. Other parts which offer reciprocation are: Lingual plate major connector. An additional occlusal rest placed on the opposite side of the tooth along with the minor connector.
  49. 49. Reciprocation.    The reciprocal arm of the clasp is positioned on the opposite side of the tooth from the retentive arm. It also stabilizes the denture against horizontal movement. It should be placed preferably at the junction of the gingival and middle thirds of the abutment tooth (always positioned above the height of contour.)
  50. 50. Encirclement.  It is the property of the clasp assembly to encompass more than 180 degree of the abutment tooth either by continuous or broken contact to prevent dislodgement during function.
  51. 51.      It can be either a continuous contact as in circumferential clasp or a broken contact as in bar clasp with at least 3 different areas of contact. The three points of contact are: retentive terminal occlusal contact reciprocal arm
  52. 52. Passivity.     A clasp in place should be completely passive. The retentive function is activated only when dislodging force are applied to the partial denture. A clasp must be completely seated on a tooth to be completely passive. If a clasp designed to reach a retentive undercut of 0.010 inch cannot reach that depth, it will exert a constant force on tooth. Over time this can produce pain or tooth movement
  53. 53.    The types of clasps are:. Circumferential or Aker ' s clasps. Vertical projection or Bar or Roach clasps .
  54. 54. Cast circumferential clasp  A clasp that encircles a tooth by more than 180 degrees, including opposite angles, and which usually has total contact with the tooth (throughout the extent of the clasp), with at least one terminal being in the infra bulge (gingival convergence) area" - GPT
  55. 55. Vertical projection clasp / Bar clasp / Roach clasp:   A clasp having arms which are bar type extensions from major connectors or from within the denture base; the arms pass adjacent to the soft tissues and approach the point or area of contact on the tooth in a gingivo- occlusal direction" - GPT.
  56. 56. Continuous clasp   A metal bar usually resting on the lingual surface of teeth to aid in their stabilization and to act as an indirect retainer" - GPT.
  57. 57. Cast Circumferential Clasp     They are popularly known as Aker’s clasps. These clasps embrace more than half of the abutment tooth. This architecture helps the clasp to hold the abutment firmly enough to prevent the rotation of the denture. They approach the undercut from an occlusal direction.
  58. 58.      Advantages: Easiest clasp to make and repair. Less food retention Best when applied in a tooth supported partial denture. Derives excellent support, bracing and retention
  59. 59.        Disadvantages : It covers a large tooth surface area. It also alters the Bucco lingual width of the crown This affects the normal food flow pattern leading to food accumulation. This causes decalcification of the tooth structure. Damage to soft tissue will occur due to lack of physiological stimulation. Difficult to adjust with pliers because of it's halfround configuration.
  60. 60.   If these clasps are placed high (more occlusally) on the tooth, the width of the food table increases leading to generation of greater occlusal forces. All cast circumferential clasps should never be used to engage the mesio buccal undercut of an abutment adjacent to the distal edentulous space (Fig. 18.167). Hence they cannot be used for cases with an undercut away from the edentulous space.
  61. 61. Types of Cast Circumferential Clasps      1. Simple circlet clasp. Most versatile and widely used. Best for tooth supported partial denture. It approaches the undercut from the edentulous space. It engages the undercut, located away from the edentulous space.
  62. 62.   Clasp can be adjusted only in one direction. They cannot be used for distal extension cases as they engage a mesio buccal undercut.
  63. 63.    2. Reverse circlet clasp or reverse approach clasp: This clasp is used when the retentive undercut on the abutment tooth is located adjacent to the edentulous space. Used in distal extension denture base to control the stresses acting on the terminal abutment teeth.
  64. 64.      Disadvantages. If sufficient occlusal clearance is not present, the thickness of the clasp has to be reduced. This will affect the strength of the clasp. An occlusal rest away from the edentulous space does not protect the marginal gingiva adjacent to the abutment tooth. Poor esthetics as the clasp runs from the mesial to the distal end of the facial surface Wedging may occur between the abutment and its adjacent tooth if the occlusal rest is not well prepared.
  65. 65.   3.Multiple circlet clasp. It is a combination of two simple circlet clasps joined at the terminal end of the reciprocal arms.
  66. 66.    It is used for sharing the retention with additional teeth on the same teeth on the same side of the arch when the principle abutment tooth has poor periodontal support. It is a mode of splinting weakened teeth. It’s disadvantages are similar to that of simple and reverse circlet clasps.
  67. 67.    4. Embrasure clasp or modified crib clasp. It is a combination of two simple circlet clasps joined at the body. It is used on the side of the arch where there is no edentulous space.
  68. 68.    The clasp must cross the marginal ridges of two teeth, emerge to cross the facial surfaces of both teeth, and engage undercuts on the opposing line angles of these teeth. Occlusal rest seat preparation must be made on both teeth Tooth structure must be removed from the buccal inclines of both teeth to provide space for adequate thickness of the metal.
  69. 69.   Indications: It is used in kennedy’s class 2 and class 3 cases without any modifications. Occasionally, a very small edentulous space can be closed by a modified embrasure clasp called a pontic clasp
  70. 70.    5. Ring clasp Indicated in tipped molars In Distal edentulous conditions with distolingual undercut - the retentive arm is extended all around the tooth from the disto buccal end to terminate in the distolingual undercut across the mesial side of the tooth
  71. 71.  As clasp is long – additional support is provided by auxiliary bracing arm
  72. 72.       Disadvantages Alteration in food flow pattern Increased tooth surface coverage Difficult to adjust or repair Contra indications Not considered in mandibular molar where attachment of the buccinator is close to tooth that the auxiliary arm encroaches on it
  73. 73.    6. fishhook or hairpin or reverse action clasp Type of simple circlet clasp. retentive arm – crosses the facial surface of the tooth from its point of origin, loops back in a hairpin turn to engage a proximal undercut below its point of origin
  74. 74.    Upper arm - rigid Lower arm - flexible Sufficient space should be present between the two arms – to avoid food accumulation & for proper finishing and polishing
  75. 75.      Indication Crown with sufficient occluso gingival height The undercut is adjacent to edentulous area Presence of a soft tissue undercut Reverse circlet can’t be used – lack of occlusal space
  76. 76.    Disadvantages Poor esthetics Tends to trap and accumulate food debris
  77. 77.    Onlay clasp ; Extension of a metal crown or onlay with buccal and lingual clasp arms. Used in occlusal surfaces of submerged abutment teeth – thus restoring the occlusal plane with an onlay.
  78. 78.   If onlay clasp is made of chrome alloy – the opposing tooth should be protected with a gold crown to avoid attrition of enamel. Used in caries resistant mouth.
  79. 79.    8. combination clasp A cast circumferential clasp can’t be used – when an undercut is adjacent to the edentulous space since it produce destructive rotatory forces on the distal abutment A flexible wrought wire retentive arm is used to replace the rigid cast alloy retentive arm.
  80. 80.   It has greater flexibility it can be placed in a deeper undercut – without any hazard to the abutment tooth It is used in maxillary canines and premolars due to its superior esthetics.
  81. 81.    Advantages The round configuration of the wrought wire – has a thin line contact which collects less debris and is easy to maintain. flex in all planes
  82. 82.     Disadvantages Tedious lab procedures Easily breaks or distorts Poor stability
  83. 83. Half and half clasp   It has a retentive arm arising from one direction and a reciprocal arm arising from another direction. Two minor connectors are needed for this design. The first minor connector attaches the occlusal rest and the retentive arm to the major connector. The second minor connector connects the reciprocal arm which is similar to the bar clasp with or without an auxiliary rest.
  84. 84.   This design produces large tooth coverage which can be reduced by converting the reciprocal arm into a short bar with an auxiliary occlusal rest. This design is intended to provide dual retention.
  85. 85.       Back-action clasp It is a modification of the ring clasp Here the minor connector is connected to the end of the clasp arm and the occlusal rest is left unsupported. Disadvantages : Lack of support to the occlusal rest reduces its function. It has both biological and mechanical unsound principles.
  86. 86.       Grasso’s clasp or VRHR clasp Developed by Grasso, This clasp consists of : A vertical reciprocal arm, an occlusal rest and a horizontal retentive arm arising separately from the major connector.
  87. 87. Grasso’s clasp or VRHR clasp  Advantages :  Minimizes tooth contact without compromise in efficacy.  Does not require the preparation of guide planes.  Suitable for posterior teeth with high survey lines.  The placement of the retentive arm is more aesthetic.
  88. 88. Grasso’s clasp or VRHR clasp   Disadvantages : Difficult to maintain as the block out zone between the base of the reciprocal arm and the tooth tends to collect food debris.
  89. 89. Rest-proximal plate – Akers retentive arm (RPA) clasp    The RPA clasp is a modified circumferential clasp The circumferential arm arises from the proximal plate adjacent to the edentulous base area. The retentive component of this direct retainer - engages a retentive undercut located on the facial surface of the abutment tooth away from the edentulous area.
  90. 90. Rest-proximal plate – Akers retentive arm (RPA) clasp    The shoulder of the clasp arm - contacts the tooth at the height of contour at the junction of the middle and gingival thirds of the tooth. This direct retainer satisfies all the requirements for use in distal-extension RPD situations. Allows for mesially oriented support, which is preferable in distal-extension RPDs.
  91. 91. Rest-proximal plate – Akers retentive arm (RPA) clasp   Excellent bracing is derived from the contact of the minor connector supporting the rest, the proximal plate contacting the tooth surface adjacent to the edentulous base area, and the shoulder part of the clasp arm. Acceptable retention is derived from retentive areas located on surfaces of the tooth away from the edentulous area.
  92. 92. Rest-proximal plate – Akers retentive arm (RPA) clasp    Requirements for adequate encirclement and passivity can easily be accommodated by this direct retainer. This type of clasp appears best suited for distalextension RPDs - where the undercut is located away from the edentulous area and for situations in which it has been determined that the tooth need not be modified to accommodate a different type of clasp.
  93. 93. Mesiodistal clasp.    This direct retainer might be considered for a tooth-borne RPD when maxillary incisors remain as the anterior abutment teeth. Although the design exhibits good supporting and bracing qualities, it may be excessively traumatic to the supporting abutment teeth when used on distal-extension RPDs.
  94. 94. Mesiodistal clasp.    Retention for this direct retainer is gained through parallelism and frictional resistance of the clasp assembly against the natural teeth. The teeth must be prepared so that their proximal surfaces are parallel or have a slight convergence to one another. This direct retainer, like the other circumferential designs, poses the same problems of covering excessive tooth structure and impairing esthetics.
  95. 95. Mesiodistal clasp.
  96. 96. Bar or vertical projection or roach clasp.    Approaches the undercut or retentive area on the tooth from a gingival direction, resulting in a push type of retention. Flexibility of the bar type of clasp can be controlled by the taper and length of the approach arm. More esthetic than the circumferential clasp.
  97. 97.    Disadvantages. 1. Greater tendency to collect and hold food debris. 2. Due to its increased flexibility of the retentive arm, it does not contribute as much to bracing and stabilization as most circumferential clasps do.
  98. 98.   Rules to use. The approach arm must always be tapered uniformly from its point of attachment at the frame work to the casp terminal.
  99. 99. Leader in continuing dental education