Minor connectors & rests & rest seats /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.

Indian dental academy provides dental crown & Bridge,rotary endodontics,fixed orthodontics,
Dental implants courses.for details pls visit www.indiandentalacademy.com ,or call

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Minor connectors & rests & rest seats /certified fixed orthodontic courses by Indian dental academy

  1. 1. MINOR CONNECTORS RESTS & REST SEATS INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com www.indiandentalacademy.com
  2. 2. MINOR CONNECTORS CONTENTS: • Definition • Functions of minor connectors • Basic principles of design of a minor connector • Types of minor connectors • Tissue stops and finish lines www.indiandentalacademy.com
  3. 3. Definition: Minor connectors can be defined as the connecting link between the major connector or base of a removable partial denture to other units of a prosthesis such as clasp assembly,indirect retainers,rests etc G.P.T-8. www.indiandentalacademy.com
  4. 4. FUNCTIONS OF A MINOR CONNECTOR 1.To transfer functional stress to the abutment teeth. Prosthesis- to- abutment function 2.To transfer the effect of retainers, rests and stabilizing components to the rest of the denture. Abutment - to - prosthesis function www.indiandentalacademy.com
  5. 5. Basic principles of design of a minor connector 1. Should be rigid 2. Should have triangular cross section with thickest portion near the lingual line angle and the thinnest portion near the buccal line angle of the tooth. 3. Should be broader buccolingually and thinner mesiodistally. 4. Should form a right angle with the major connector so that the gingival crossing is abrupt and cover as little gingival tissue as possible. 5. Sharp angles should be avoided and spaces should not exist for trapping of food debris. 6.Should never be placed on the convex lingual surfaces of the tooth where its bulk will be www.indiandentalacademy.com evident.
  6. 6. Types of minor connectors 1. Join clasp assembly to the major connector. 2. Join indirect retainers and auxilary rests to major connector. 3. Join denture base to the major connector 4. Serve as an approach arm for a vertical projection or bar type of clasp www.indiandentalacademy.com
  7. 7. 1.Minor connectors joining clasp assembly to major connector - Rigid www.indiandentalacademy.com
  8. 8. • Minor connectors contacting the guide plane surfaces are as broad as 2/3 the distance between the tips of adjacent buccal and lingual cusps of the abutment tooth. • They should extend gingivally contacting an area of the abutment tooth from the marginal ridge to 2/3 the length of the enamel crown. • If no clasp arm is formed as when a bar clasp originates elsewhere, the connector should be tapered to a knife edge the full length of the buccal surface. www.indiandentalacademy.com
  9. 9. • When an artificial tooth is to be placed the thickest portion should be at the lingual line angle of the abutment tooth.This way bulk is ensured with least interference to the placement of the artificial tooth. • If the clasp assembly is not being placed on a tooth adjacent to the edentulous space, the minor connector must be positioned in the embrasure between two teeth. www.indiandentalacademy.com
  10. 10. 2. Minor connectors that join indirect retainers or auxiliary rests to major connector - Should form a right angle with the major connector - Should lie in embrasure between teeth to disguise its www.indiandentalacademy.com bulk as much as possible.
  11. 11. 3.Minor connectors that join the denture base to the major connector • It should be rigid enough to support and resist breakage of the denture base. • In maxillary distal extension cases it should extend up to the maxillary tuberosity. • In mandibular distal extension case the minor connector should cover 2/3 the length of edentulous ridge. 3 types: 1. Lattice work construction 2. Mesh construction 3. Bead,wire or nail head minor connector www.indiandentalacademy.com
  12. 12. 1.Open latticework construction •Consists of longitudinal and transverse struts that form a ladder like network www.indiandentalacademy.com
  13. 13. • In the mandibular arch, one longitudinal strut should be positioned buccal to the crest of the ridge and one should be positioned lingual to the crest of the ridge. • In the maxillary arch, one longitudinal strut should be positioned buccal to the crest of the ridge and the border of the maxillary major connector will act as the second longitudinal strut. • Transverse struts should be placed such that they do not interfere with tooth placement. relief should be given between struts and the ridge for acrylic to flow. This is done with the help of tissue stops. • Relief provides space between minor connector and tissues of the residual ridge.the space permits an acrylic resin to encircle longitudinal and transverse struts. www.indiandentalacademy.com
  14. 14. Advantages • Provides the strongest attachment of the acrylic resin denture base to the removable partial denture. • Easiest to reline if necessary because of ridge resorption. www.indiandentalacademy.com
  15. 15. 2.Mesh construction Rigid metal screen with channels that pass through the connector which are intended to permit acrylic resin penetration,which allows resin encirclement of the minor www.indiandentalacademy.com connector and mechanical retention of denture base.
  16. 16. • Main drawback is that it is more difficult to pack acrylic resin dough because more pressure is needed against the resin to force it through the small holes. • It also does not provide as strong an attachment for the acrylic denture base as compared to the lattice framework www.indiandentalacademy.com
  17. 17. 3.Bead ,wire or nail head retention minor connector - Used with a metal denture base which is cast to fit directly against thewww.indiandentalacademy.com Hence no relief edentulous ridge. is provided beneath this minor connectors.
  18. 18. • Retention of the acrylic resin is obtained by projection of metal on its surface These projections may be in the form of beads,wires or nail heads. Advantages: • Most hygienic • Thermal stimulation www.indiandentalacademy.com
  19. 19. Disadvantages: -Difficulty to adjust the metal base. -Cannot be adequately relined in case of ridge resorption. -Weakest attachment. www.indiandentalacademy.com
  20. 20. Tissue stops -Used on all distal extension partial dentures using latticework or mesh retention. www.indiandentalacademy.com
  21. 21. FINISH LINES • The term finish line in a partial denture denotes the junction between the acrylic denture base and major connector or any polished metal surface. • To provide sufficient bulk of acrylic resin to produce a smooth and even joint with the metal framework, provision must be made to provide space for a butt joint so that the acrylic resin can be finished evenly with the major connector. 2 types - Internal finish line www.indiandentalacademy.com - External finish line
  22. 22. • Resin-metal interfaces must be created on both internal and external surfaces of associated major connectors. • In case of metal base minor connectors, acrylic resin is processed only on the external surface. Therefore resinmetal interfaces should be created only on external surfaces. • These resin-metal interfaces are referred to as finish lines and if they are located on the outer surface of the major connector, they are called external finish lines and if they are positioned on the inner or tissue surfaces they are termed as internal finish lines www.indiandentalacademy.com
  23. 23. • Internal finish line • External finish line www.indiandentalacademy.com
  24. 24. Internal finish lines : • They are formed as a result of relief wax placed on the edentulous ridge prior to duplication. The relief wax creates an elevated area on the resultant refractory cast. The margins of the relief wax establish internal finish lines in the completed metal frame work. Margins should be sharp and well defined. External finish lines: • This also must be sharp and should be slightly undercut to help lock the acrylic resin to the major connector.the internal angle formed at the junction of major and minor connector should be less than 90 degrees. • An external finish line is formed by the placement and carving of the wax during framework fabrication.the contours of external finish line should be consistent with the www.indiandentalacademy.com contours of major connector.
  25. 25. 4. Minor connectors that serve as an approach arm for vertical projection or bar type of clasp The only minor connectors that are not required to be rigid.these components supports direct retainers and therefore must exhibit some degree of flexibility.a minor connector of this type approaches the tooth from an apical direction rather www.indiandentalacademy.com than from an occlusal direction
  26. 26. RESTS AND REST SEATS www.indiandentalacademy.com
  28. 28. INTRODUCTION The forces acting on the occlusal surface of a partial denture must ultimately be absorbed by the alveolar bone, through underlying soft tissues and teeth supporting the partial denture. controlling factor in the triad of prosthesis-tooth- periodontium. Since Bonwill (1899) first introduced and recommended the use of rests in RPD, the use of rests have been inviolate and has gone unchallenged. www.indiandentalacademy.com
  29. 29. DEFINITION According to glossary of Prosthodontic terms: 1. Rest - is a projection or attachment, usually on the side of an object . 2. Rest seat - is the prepared recess in a tooth or restoration created to receive the occlusal, incisal, cingulum or lingual rest. www.indiandentalacademy.com
  30. 30. According to Ernest L. Miller: • Rest - is a projection of the clasp which lies in a prepared recess of the abutment tooth and acts to support and stabilize the removable partial denture. • Rest seat - The prepared recess in a tooth created to receive the occlusal, incisal or lingual rest. www.indiandentalacademy.com
  31. 31. According to McCracken’s • Rest - Any unit of a partial denture that rests on a tooth surface to provide vertical support. • Rest seat - The prepared surface of an abutment to receive the rest www.indiandentalacademy.com
  32. 32. HISTORICAL REVIEW • Russell states that rest is a rigid extension of a partial denture that contacts the remaining tooth structure to dissipate functional forces. • According to Grant A.A. and Johnson W. a rest is an extension from partial denture which is positioned on the surface of a standing tooth capable of providing resistance to displacement of the denture in tissueward direction. www.indiandentalacademy.com
  33. 33. • Kratochvil stated that rest must be positive and should not allow the prosthesis to slide off the tooth. They must provide a positive connection between prosthesis and tooth. • McGregor and Stewart et al stated that rests maintain clasps in their correct position, prevent food impaction and prevent the denture from sinking into or causing overdisplacement of the soft tissues. www.indiandentalacademy.com
  34. 34. CLASSIFICATION/TYPES • According to McCracken, on the basis of tooth surface prepared to receive them: • Occlusal • Incisal • Lingual/cingulum www.indiandentalacademy.com
  35. 35. According to Stewart,on the basis of function they serve : • Primary rests • Secondary or auxiliary rests According to Kratochvil, on the basis of their location in the arch, rests can be : • Anterior rests • Posterior rests www.indiandentalacademy.com
  36. 36. FUNCTIONS OF THE RESTS • The primary purpose of the rest is to provide vertical support for the partial denture and thus resist the movement in a cervical direction . -maintains components in their planned positions - Provide reciprocation and stabilization. www.indiandentalacademy.com
  37. 37. • It transmits vertical load as well as the horizontal forces to the tooth. www.indiandentalacademy.com
  38. 38.  Directs and distributes occlusal loads to the abutment teeth and directs forces in the long axis of the teeth www.indiandentalacademy.com
  39. 39. • • • • Provide rigid prosthetic support. Maintains established occlusal relationships by preventing settling of the denture. Prevent supra eruption. Restore occlusion. www.indiandentalacademy.com
  40. 40. • Deflection of food by bridging the gap between two teeth www.indiandentalacademy.com
  41. 41. • Prevents impingement of soft tissues. • Protects the denture/abutment tooth junction. www.indiandentalacademy.com
  42. 42. • Restore anterior guidance- anterior rests. • Restores anterior anatomy as required. • Provides positive seat by extending over the incisal edge. www.indiandentalacademy.com
  43. 43. • Splints mobile teeth. www.indiandentalacademy.com
  44. 44. BASIC CONSIDERATIONS FOR RESTS AND REST SEATS • Rests should be placed in properly engineered recesses, in the surfaces of the teeth. • The recess should be prepared within the confines of the greatest tooth massmore PDL fibers. • Vertical stress will be resisted by all of the fibers. www.indiandentalacademy.com
  45. 45. • Floor of rest seat 1. Floor of the recess should be less than 90° to the long axis of the tooth- to direct stresses axially. 2. Apical to the marginal ridge. www.indiandentalacademy.com
  46. 46. • Rest should not be placed on inclined tooth surfaces- www.indiandentalacademy.com
  47. 47. • Anterior rests should be as close to the center of the tooth as possible. • Positioned in line with the residual ridge. www.indiandentalacademy.com
  48. 48. Rounded in all aspects (no sharp line angles). Minimal preparation in dentin. www.indiandentalacademy.com
  49. 49. • Center should be deeper than the surrounding rest surface. www.indiandentalacademy.com
  50. 50. Anterior positioning of the rest and the rotation axis to favor biomechanics: 1. Forward and downward movement, disengagement of Direct retainer. 2. More vertical direction of forces. 3. More advantageous vertical support from denture base area. www.indiandentalacademy.com
  51. 51. • Placed as close to the gingiva and bone as possible to reduce leverage. www.indiandentalacademy.com
  52. 52. Placement of rest on tooth surface away from edentulous area• Tipping force in opposite direction • Maintain contact with adjacent teeth results • Multiple tooth support • Favorable direction of force www.indiandentalacademy.com
  53. 53. Basic requirements of rests and rest seats • Provides rigid support. • Extends to center of the tooth in tooth supported situations. • Rounded, with no sharp angles (for ease of cleaning, making impressions, prevent tooth fracture). www.indiandentalacademy.com
  54. 54. • No undercuts in the path of insertion. • Minimum of 1 mm thick. • Restores the occlusal plane. • Provides reciprocation. • Contoured so that when increased force is applied to the prosthesis the rest will engage more securely to prevent separation. www.indiandentalacademy.com
  55. 55. OCCLUSAL REST AND REST SEAT Outline form • Rounded triangle with the base resting on the marginal ridge and apex toward the center of the occlusal surface. • Should follow outline of mesial or distal fossa. • Dimensions- ½ the buccolingual width from cusp tip to cusp tip and 1/3 to ½ the mesiodistal width. Is as long as it is wide, should be at least www.indiandentalacademy.com 2.5 mm for both molars and premolars.
  56. 56. Reduction of the marginal ridge of approximately 1.5 mm is usually necessary. Junction of occlusal rest to the abutment should be shallow ball and socket joint in distal extension cases. The floor of the occlusal rest seat should be apical to the marginal ridge and the occlusal surface. - Can be concave, or spoon shaped- for distal extension. - Can be box shaped- for tooth www.indiandentalacademy.com supported.
  57. 57. • Rest seats not prepared opposing functional cusps. • In tooth borne cases rest must be extended to the center of the tooth. • Minimum metal thickness is 0.5mm at thinnest point and 1-1.5mm at marginal ridge. • proximo-occlusal line angle of the preparation should not be sharp. www.indiandentalacademy.com
  58. 58. Preparation of occlusal rest. Armamentarium for rest preparation: Preparation in enamel: www.indiandentalacademy.com
  59. 59. Method of obtaining positive support Rest seat preparations in sound enamel. • Preparation of occlusal rest seats always must follow proximal preparation, never precede it. • Occlusal rest seats in sound enamel may be prepared with diamond points of approximately the size of nos. 6 and 8 round burs or with carbide burs. Occlusal rest seat prep. in existing restoration. • It is same as in enamel. Proximal preparation first and then rest seat should be placed. • Rest seat preparation in amalgam should be avoided because of creep. • Though some compromise is permissible, the basic principles of rest seat preparation should not be violated. When perforation occurs it may be filled with gold foil. www.indiandentalacademy.com
  60. 60. Occlusal rest seats in new restoration. should be placed in the wax pattern. • - The location of the occlusal rest should be shown when the tooth is prepared for a crown or an inlay so that sufficient clearance may be provided in the preparation for the rest. • - They • Occlusal rest seats in crown/inlays/onlays. • • • • • • Most ideal way of getting positive support. - Indicated in - rotated/inclined tooth. - mandibular bicuspid with rudimentary cusp. - abraded tooth. - These are generally made larger and deeper than the enamel. - Those made in abutment crowns supporting tooth borne dentures maybe slightly deeper than those in abutments supporting a distal extension base. - www.indiandentalacademy.com
  61. 61. Types of occlusal rests. Internal Occlusal rests • A totally tooth supported partial denture may use internal occlusal rests for tooth occlusal support and horizontal stabilization. • An internal occlusal rest is not an internal attachment . • Occlusal support is derived from the floor of the rest seat and from an additional occlusal bevel if provided. www.indiandentalacademy.com
  62. 62. • Horizontal stabilization is from the near-vertical walls of this type of rest seat. • Should be parallel to the path of placement slightly tapered occlusally and dovetailed to prevent dislodgement proximally. Advantage: Advantage • Facilitates the elimination of visible clasp arm buccally • Permits the location of the rest seat in a more favorable position in relation to the “tipping” axis of the abutment. Retention provided by lingual clasp arm lying in a natural or prepared infrabulge area on the abutment tooth. www.indiandentalacademy.com
  63. 63. Long Or Continuous Rests Splinting periodontally weakened teeth • The long or continuous rest can serve as an effective stabilizing or unifying device. The rest can be designed to extend entirely across the occlusal surface of two or more teeth and, in some instances, across the entire arch. • When occlusal force is delivered in one area, all the remaining teeth act in unison to provide support. With planning, this type of rest can restore the occlusal plane, provide support, and splint the arch. www.indiandentalacademy.com
  64. 64. Control position of unopposed teeth Many times a situation exists in which a tooth has lost its antagonist in the opposing arch but does not need a replacement for masticating functions. Extending the rest in the partial denture planning and design not only gains support from that tooth but also holds it in position, preventing elongation and eliminating the necessity of a second prosthesis in the opposing arch. www.indiandentalacademy.com
  65. 65. Inter Proximal Occlusal Rests ( embrasure rest) The design of a direct retainer assembly may require that interproximal occlusal rests be used. Interproximal occlusal rest seats are prepared as individual adjoining occlusal rest seats. Preparations must be extended farther lingually. The lingual interproximal area requires only minor preparation. www.indiandentalacademy.com
  66. 66. Adjacent rests rather than a single rest are used to - Avoid inter proximal wedging by the framework. - Also to shunt the food away from contact points. Care must be exercised to avoid eliminating contact point of abutment teeth. Sufficient tooth structure must be removed to allow for adequate bulk of the component to bewww.indiandentalacademy.com so shaped that
  67. 67. EXTENDED OCCLUSAL REST Indicated - in Kennedy class II, modification 1 and Kennedy class III situations when the most posterior abutment is a mesially tipped molar 1. Minimize further tipping of the abutment forces are directed down the long axis of the abutment. 2. This rest should extend more than one-half the mesiodistal width of the tooth, be approximately one-third the buccolingual width of the tooth. 3. If abutment is severely tilted the extended occlusal rest may be in the form of an onlay. www.indiandentalacademy.com
  68. 68. LINGUAL RESTS(Cingulum rests) Anterior teeth may be used to support an indirect retainer or auxiliary rest. Canine is preferred over an incisor as an indirect retainer or an auxiliary rest. Normal morphology requires minimal tooth preparation. When a canine is not present, multiple rests that are spread over several incisor teeth are preferable to the use of a single incisor. Lingual rest should be kept near the center of rotation. www.indiandentalacademy.com
  69. 69. Preferable to an incisal rest - It is placed nearer the horizontal axis of rotation (tipping axis) of the abutment , less tendency to tip the tooth. - More esthetically acceptable. A lingual rest may sometimes be placed in an enamel seat at the cingulum or just incisally to the cingulum. Lingual rest seat preparations in enamel are rarely satisfactory on mandibular anterior teeth because of a lack of thickness of enamel in which to prepare a seat of adequate www.indiandentalacademy.com form to be truly supportive.
  70. 70. Outline form A slightly rounded V(half moon shaped) is prepared on the lingual surface at the junction of the gingival and the middle -one third of the tooth. The apex of the V is directed incisally. The floor of the rest seat should be toward the cingulum rather than the axial wall. Care must be taken not to create an enamel undercut, which interferes with placement of the denture. preparation is broadest at lingual aspect.. Dimensions – mesiodistal width = 2.5-3mm, labiolingual width = 2mm, incisoapical depth = 1.5mm www.indiandentalacademy.com
  71. 71. Preparation Preparation may be started by using an inverted cone-shaped diamond stone and progressing to smaller, tapered stones with round ends to complete the preparation. All line angles must be eliminated, and the rest seat must be prepared within the enamel and must be highly polished. A predetermined path of placement for the denture must be kept in mind in preparing the rest seat. www.indiandentalacademy.com
  72. 72. Method of obtaining support In a cast restoration Plan and execute a rest seat in the wax pattern Contour of the framework restores the lingual form of the tooth. Cast Co-Cr rest seats attached to lingual surface of anterior teeth Composite may be added to lingual surface www.indiandentalacademy.com
  73. 73. Inlay with pins Crowns / onlays www.indiandentalacademy.com
  74. 74. INCISAL RESTS AND REST SEATS Less desirable - more unfavorable leverage than lingual rest - orthodontic movement of the tooth Incisal rests are placed on prepared rest seats at the incisal angles of anterior teeth Used predominantly as auxiliary rests or as indirect retainers. May be used on a canine abutment in either arch, but more commonly on the mandibular canine. Provides definite support , relatively little loss of tooth structure and little display of metal. www.indiandentalacademy.com
  75. 75. Outline form  Small ‘V’- shaped rounded notch is prepared at the incisal angle of a canine or on the incisal edge of an incisor, with the deepest portion of the preparation apical to the incisal edge. Dimensions - 2.5 mm wide and 1.5 mm deep. The notch is beveled both labially and lingually, and the lingual enamel is shaped to accommodate the rigid minor connector connecting the rest to the framework. The floor of rest seat is extended slightly onto the labial aspect of tooth. www.indiandentalacademy.com
  76. 76.  Incisal rest is placed either at mesioincisal or distoincisal angle.  It can be incorporated into a lingual plate – for additional stabilization.  Multiple incisal rests can be placed for additional support. www.indiandentalacademy.com
  77. 77. Summary and conclusion • Rests and rest seats deserve special consideration in removable partial denture construction. Proper understanding of the functions, biomechanical design and placement of the rests is necessary in partial denture treatment. • Rests play a crucial role in maintaining health of supporting structures. • The topography of any rest should be such that it restores the www.indiandentalacademy.com topography of the tooth existing before the rest seat is prepared.
  78. 78. References • A.A. Grant, W. Johnson: Removable denture prosthodontics. 2nd edition. • Albert Seidin. Occlusal rests and rest seats. J Prosthet Dent. 1958; 8:431440 • Bert T Cecooni. Effect of rest design on transmission of forces to abutment teeth. • J Prosthet Dent. 1974; 32:141-151 Davenport, Basker and Heath :A color atlas of removable partial dentures, 1st edition, 1980. • Ernest L. Miller, Joseph www.indiandentalacademy.comdenture prosthodontics. 2nd E. Grasso : Removable
  79. 79. Frank J. Kratochvil. Influence of occlusal rest position and clasp design on movement of abutment teeth. J Prosthet Dent. 1961; 13:114-121 Kratochvil Partial removable prosthodontics. Ist edition, 1988, W.B.Saunders. Mc Cracken’s Removable partial denture prosthodontics. 11th edition, 2004. Stewart, Rudd and Kuebker: Clinical Removable denture prosthodontics. 2nd edition, 2001. www.indiandentalacademy.com
  80. 80. - Clinical removable partial prosthodontics, 2nd edition Kenneth L Stewart - Removable partial prosthodontics,2nd edition , Ernest L Miller - McCrackens Removable partial prosthodontics, 8th edition Glen p McGivney - Colour Atlas of Removable Partial dentures, John C Davenport www.indiandentalacademy.com
  81. 81. www.indiandentalacademy.com