Non rigid connectors in fixed prosthesis / cosmetic dentistry training


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Non rigid connectors in fixed prosthesis / cosmetic dentistry training

  1. 1.
  4. 4. NON-RIGID CONNECTORS • Precision attachments. KEY AND KEYWAY. Tube and screw attachment. Procedure of fabrication. Custom milling machine. • SPLIT PONTIC • CROSS PIN AND WING • Conclusion • References
  5. 5. Introduction
  6. 6. • Connectors are those parts of a fixed partial denture (FPD) that join the individual retainers and pontics together. In most of the cases stress concentration is found in the connectors of the prosthesis. • They are of two types that is Rigid and Nonrigid connectors.
  7. 7. • Rigid connectors could be made by casting, soldering and welding. • The design and fabrication of multi unit fixed prosthesis may be a complication, where abutment teeth are malaligned. • In such situations to attain a common path of insertion, non rigid connectors can be used. These connectors permit limited movements and can be made by use of prefabricated inserts or prefabricated wax patterns.
  8. 8. Definitions
  9. 9. GPT-8 • Connector- The portion of fixed partial denture that unites the retainer and pontic • Non-rigid connector: - a connector that permits limited movement between otherwise independent members of a fixed partial denture.
  10. 10. FPD with nonrigid connector. A, Mortise pattern (female) positioned on distal of the canine retainer. B, FPD assembled with prefabricated resin tenon (male) on mesial of pontic.
  11. 11. • Internal connector: - a non-rigid connector of varying geometric design’s using a matrix to unite the members of a FDP • Sub-occlusal connectors: - an interproximal non-rigid connector positioned apical to and not in communication with the occlusal plane.
  12. 12. Indications • Malaligned abutments without common path of insertion • Existence of pier abutments • Long span FPD s, which can distort due to shrinkage of porcelain • Distal abutment with questionable prognosis • Presence of numerous mobile teeth which need to be splinted by fixed
  13. 13. Contraindications • Teeth with large pulp chambers • Abutment with reduced clinical crown height
  14. 14. Principles of connector design
  15. 15. • The connector design determines the success of FDP to a certain extent. The factors to be observed while fabricating a connector are: - • Type of connector -Rigid connector -Non-rigid connector. • Size of connector • Shape of connector
  16. 16. 1. Type of connectors 1. Rigid connector- they are the ideal choice of connectors for FDP • They provide maximum rigidity and accurately transfer occlusal forces to abutment teeth.
  17. 17. • 2. Non rigid connector- they are usually used for pier abutments due to differences in physiologic tooth movement and difference in arch position of abutment. • It provides a scope for flexing of mandible during opening and closing movements but it is technically sensitive.
  18. 18.
  19. 19. • Size of connector • The size of connector is important in maintaining the periodontal health of the abutment teeth. • The recommended occlusogingival height of connector is, ideally 3-4 mm. It should be sufficiently large to prevent distortion /fracture during function.
  20. 20. • For anterior teeth connector should be placed lingual and use of large connector /inappropriately shaped connector result in display of metal leading to esthetic failure of FDP
  21. 21. • Shape of connector • Connector’s should have a concave shape mesiodistally (appear as meniscus) and Convex buccolingually. In cross section it appears elliptical • So usually the long axis of ellipse is placed perpendicular to long axis of force. It should be highly polished.
  22. 22.
  23. 23. • Connectors are basically classified as: - • Rigid connectors- • Cast connectors • Soldered connectors • Welded connectors • Loop connectors
  24. 24. • Non rigid connectors • Key & keyway (dovetail) • Split pontic • Cross pin and wing • Screw and tube
  25. 25. • Nonrigid connectors are generated through incorporation of prefabricated inserts in the wax pattern or • Through custom milling procedures after the first casting has been obtained.
  26. 26. • The second part is then custom-fitted to the milled retainer and cast. They are often made with prefabricated plastic patterns. • The retainers are then cemented separately and fitted to each other in metal.
  27. 27.
  28. 28. • The design of nonrigid connectors that are incorporated in the wax pattern stage consists of a mortise (also referred to as the female component) prepared within the contours of the retainer and a • Tenon (male) attached to the pontic.
  29. 29. • The mortise is usually placed on the distal aspect of the anterior retainer. • Accurate alignment of the dovetail or cylindrically shaped mortise is critical; it must parallel the path of withdrawal of the distal retainer.
  30. 30. • Paralleling is normally accomplished with a dental surveyor. • When aligning the cast, the path of placement of the retainer that will be contiguous with the tenon is identified.
  31. 31. Keyway position?
  32. 32.
  33. 33.
  34. 34. • The custom milling machine is a device used for working or forming materials into a desired form, to blend materials or to perform other mechanical properties.
  35. 35. Custom milling machine. Non-rigid connectors in fixed prosthodontics :current concepts and case reports.JIPS2005;5:2,99-102
  36. 36. It has following three functions: 1. First, as a surveyor to determine path of insertion. 2. Second, to allign attachments or other assemblies very accurately. 3. In milling, a process of wax or metal in line, angled or parallel shaping to given contours, depending upon the type of work with the added advantage that it can be used for angled or parallel drilling.
  37. 37. • There are different types of non-rigid connectors: - • Key and keyway (Dovetails). • Screw and tube attachment. • Split pontic. • Cross pin and wing.
  38. 38. • Non-rigid connectors are classified into two types based on method of fabrication 1.Precision 2.Non-precision /semi precision Precision attachment is defined as a retainer consisting of a metal receptacle and a closely fitting part.
  39. 39. PRIESKEL in 1979 classification: • Intra coronal attachments • Extra coronal attachments Based on mechanism of retention intra coronal are sub classified as: Group 1-entire frictional Group 2-mechanical lock
  40. 40. • Extra coronal are divided into: 1. Projection units 2. Connecting units 3. Cross-linked attachments Non-rigid connectors used in FPD is either an intra coronal or semi precision type
  41. 41. Extra coronal attachments
  42. 42. • Precision attachments are prefabricated metal units with parallel sided walls • Semi precision are intra coronal attachments with tapered walls prepared in laboratory
  43. 43. • Semi precision (developed by Thompson, Nevrohr and Sherer) • Feature significant taper • May be cast from patterns or entirely lab produced • Precision fit is not as easily attained as with prefabricated attachments but advantage of their adaptability in different restorations make them very valuable
  44. 44. • Consists of 2 parts: • Simple channels closed at one end to provide a stop MATRIX. • Solid slid which fits accurately into channel known as PATRIX.
  45. 45. • This type of attachment fit rigidly together when articulated so they will resist movement except passage along a line/path of insertion or withdrawal.
  46. 46. • Also called as Deep Seat Rests where patrix or matrix is cast to fit its other half. • Retention provided by attachment depends on contact between two components, it is desirable to provide as much surface area as possible, surface area available is product of cross section of male part and its length.
  47. 47. Key and keyway (dovetails) This is a passive attachment that can be constructed in the laboratory or preformed plastic patterns can be used and incorporated in wax patterns. It is used to overcome a slight lack of parellelism of prepared abutment teeth. It is also used as a means of reducing the forces on the retainer.
  48. 48. Milled tapered keyway Mesial surface of pontic Carried a key.
  49. 49. Procedure
  50. 50. • The wax pattern for the retainer on the pier abutment is fabricated on the working cast. • When a plastic pattern is used for the key and keyway, a deep box form is carved into the distal surface of the wax pattern to create space for the placement of the plastic keyway pattern.
  51. 51. • Adequate depth and a parallel path of insertion are essential when preparing the box form in the distal of this abutment.
  52. 52.
  53. 53. • Place the working cast, with the wax pattern seated, on the table of a surveyor. • Assemble the key and keyway portions of the connector, and lock the mandrel that extends from the top of the key portion of the pattern into the vertical spindle of the surveying instrument.
  54. 54. • Manipulate the surveying instrument. Manipulate the surveyor table until the mandrel and attachments are parallel with the path of insertion of the distal preparation
  55. 55. The cast is manipulated until the insertion path of the distal abutment Preparation parallels the mandrel(b) projecting from the key-keyway Assembly. The keyway pattern is luted to the retainer wax pattern on surveyor To maintain the relationship
  56. 56. • Then lower the plastic pattern to the middle retainer wax pattern and lute it in place with sticky wax • Remove the key portion and complete the middle retainer wax pattern by blending the distal surface with the keyway.
  57. 57. • The pattern is then invested, burned out, and cast. After the casting has been cleaned and air abraded, carefully cut off any part of the keyway portion of the attachment that protrudes above the occlusal surface. • Place the casting on the working cast, and place the prefabricated plastic pattern for the key into the keyway. • At this point the pontic wax pattern is attached to the pontic key.
  58. 58. • The pontic pattern is completed, removed from the working cast, invested, burned out and cast. • After the casting is recovered from the investment, the mandrel and any excess on the top portion of the key are carefully reduced so the key and keyway are flush.
  59. 59. Mesial segment of keyway Cemented first Distal segment cemented After that
  60. 60. • Moulding m b (1992) : - “An alternate orientation of non-rigid connector in FPD”. • Conventional orientation: - Keyway within distal surface of anterior retainer of mesial segment. • Keyway opening on occlusal surface with taper diverging occlusally. The mesial segment is delivered 1st and then distal segment is seated with the key sliding in the keyway of the anterior retainer. “An alternative orientation of non-rigid connectors in F.P.D” J.Prosthet. Dent68, 236-8,1992
  61. 61. • The main disadvantage of this system is need of increased tooth reduction on distal surface of anterior abutment/ leads to over contouring of distal surface of mesial retainer.
  62. 62. An alternative orientation of non-rigid connectors in F.P.D” J.Prosthet. Dent68, 236-8,1992 Traditional orientation of non rigid connector
  63. 63. • The author described an alternative orientation by reversing key and keyway. • Key is attached to distal surface of anterior retainer and is inverted so that it taper converges occlusaly.
  64. 64. • The keyway is also inverted and incorporated in the mesial surface of the pontic. • The mesial segment is seated first at delivery followed by distal segment, with the keyway sliding over the key of the anterior retainer.
  65. 65. Conventional orientation with tilted molar And overtapered distal surface of premolar abutment
  66. 66. Inverted orientation with tilted molar, Illustrating the normal abutment preparation And improved contours of the retainers. Key on anterior retainer and keyway on pontic
  67. 67. Advantages: - • Conservative tooth preparation: - as key is place extracoronally, improves retention, stability and maintain pulpal integrity. • Physiologic axial contour: - prevents over contouring of distoaxial surface of anterior retainer • A flat emergence profile and physiologic contour of gingival 1/3rd can be developed.
  68. 68. An alternative orientation of non-rigid connectors in F.P.D J.Prosthet. Dent68, 236-8,1992 • This inverted orientation allows more flexibility in positioning the angled connector while maintaining the desired embrasure facially, lingually and gingivally. • The principles of biologic contours are then realized with physiologic emergence angles.
  69. 69. • Esthetic potential- inverted orientation of non-rigid connection can be more esthetically pleasing in PFM FPD’S. • Since the keyway opening is open the tissue surface of pontic the only visual evidence do the connector is the interface between the metal guiding planes of the two segments.
  70. 70. Disadvantage- • The opening of key and key-way, the porcelain metal junction are positioned on tissue surface of pontic with tissue- contacting pontics the space between the key and the keyway is an area for plaque retention and resultant tissue irritation. • This can be avoided by use non tissue- contacting pontic.
  71. 71. Screw and tube attachment Precision attachments: A link to successive restorative treatment Gareth jenkins
  72. 72. Screw and tube attachment • It consists of two or three parts. • A screw with a tapered head and threaded tube. • length varying from 5 to 8.1mm and diameter varying from 1.6 to 2 mm.
  73. 73. • The tubes can be cast into or soldered to the substructure or incorporated into extensions off a conventional retainer. • The collar is cast into the superstructure and the screw with its tapered head unites the two parts.
  74. 74. • Useful for 1.Overcoming alignment problems 2.Connecting one restoration or fixed partial denture to another.
  75. 75. An acrylic temporary Restoration was made in two parts to overcome Allignment problems between Molar and premolar Acrylic copings were used to Record the occlusion
  76. 76. Acrylic copings used To articulate the model Fpd was waxed up
  77. 77. Attachment inserted Slight distally Wax pattern was cut back And angled to same path of Insertion as mesial abutment
  78. 78. Cut back of wax pattern And a stainless steel wire Which was at same angulation To mesial abutment Completed cating and grooves Were milled in buccal and Lingual surfaces of block
  79. 79. Tube was placed in casting And soldered from undersurface Of pontic
  80. 80. A plastic pin was inserted Into the hole left by the Removal of stainless steel wire The screw was placed in the Tube and the wax up of the Mesial abutment and Superstructure was completed.
  81. 81. Srew was removed and Wax pattern was ready for casting Second casting was placed in model And checked for accuracy of fit And localisation of screw in tube.
  82. 82. Completed fixed partial denture
  83. 83. Commercially available attachments which can be used to overcome allignment problems Rod and tube attachment. Stern Tube lock. APM-Sterngold
  84. 84. Preat-Contur. Slide attachment tapering From occlusal to cervical area. Matrix and patrix are plastic Burn out patterns
  85. 85. Dovetail slide attachment By prof.Beyler Posterior fixed partial Dentures with minor Allignment problems of Abutment and as connector
  86. 86. Split pontic • This is an attachment that is placed entirely within the pontic. • It is particularly useful in tilted abutment cases, where the use of a conventional dovetail would necessitate the preparation of a very drastic box in the distal aspect of the pier abutment.
  87. 87. • The wax pattern of the anterior three-unit segment (mesial retainer-pontic –pier retainer) is fabricated first, with a distal arm attached to the tissue-contacting area of a pontic.
  88. 88. • A surveyor is used to position either the key or the keyway segment of fpd pattern, pointing occlusally. • This segment must align with the distal abutment preparation.
  89. 89. • Invest, burnout and cast the mesial three- and –a-half –unit segment. After preliminary finishing, seat the cast segment on the working cast.
  90. 90. • Wax the distal retainer and the disto- occlusal two-thirds of the pontic pattern.
  91. 91. • Try it on the prepared teeth in the mouth, making adjustments as necessary. Cement the mesial segment first, followed immediately by the distal segment. • No cement should be placed between the two segments of the pontic.
  92. 92. Mesial segment which is Cemented first had the distal shoe that is gingival Portion of pontic Distal segment covers the Mesiogingival part of pontic When the distal retainer Is cemented.
  93. 93. Cross-pin and wing • The cross pin and wing are the working elements of a two-piece pontic system that allows two segments to be rigidly fixed after the retainers nave been cemented on their respective abutment preparations.
  94. 94. • The design will find use primarily in accommodating abutment teeth with disparate long axes. • The path of insertion of each tooth preparation is made to parallel the long axis of that tooth.
  95. 95. • Attach a vertical wing, cut out of a piece of base plate wax, to the mesial surface of the distal retainer wax pattern. • The wing should parallel the path of insertion of the mesial abutment preparation
  96. 96. • It should extend out 3.0mm mesially from the distal retainer, • Have a 1.0mm thickness faciolingually, be 1.0mm short of the occlusal surface, • Have an undersurface that follows the intended contour of the underside of the pontic.
  97. 97. • Invest, burnout, and cast the distal retainer, with wing. Seat the retainer on the cast, and drill a 0.7mm hole through the wing with a twist drill in a hand piece. • Place a 0.7mm diameter pencil lead through the hole and build the wax pattern around the lead and the wing.
  98. 98. • Remove the lead, with draw the retainer- pontic wax pattern, and replace the 0.7mm lead in the pontic pattern to maintain the patency of the hole during investing and casting.
  99. 99. • Assemble the two parts of the fixed partial denture on the working cast. • Use a tapered 8/0 machinist reamer to ream a smooth, tapered hole through pontic and wing, following he pilot hole produced by the 0.7mm pencil lead.
  100. 100. • Fabricate a pin of the same alloy used for the fixed partial denture casting. • A mold can be made by drilling a hole in a piece of aluminum with the machinist reamer and filling the hole with auto polymerizing resin
  101. 101. The distal retainer and Wing are cemented first The retainer pontic segment Are seated last
  102. 102. A tapered pin is driven Through the pontic, the wing And back out through the pontic Completed cross wing and pin Fixed partial denture.
  103. 103. Tapered cross pin attachments for fixed bridges. Operative dentistry,1994,19,7-10. F.C. Eichmiller The wax pattern of the attachment wing on one of the Abutments. Wing should extend 3mm into pontic space and have Gingival contour matching the Contour of final pontic. Wing should Be oriented parallel with pontic segment
  104. 104. Casting with hole in wing to Receive 0.7mm lead pattern
  105. 105. Pontic segment pattern formed Over the wing and lead The castings are fit to the Model and pin hole is reamed To a taper with an tapered Pin reamer.
  106. 106. Acrylic pattern used to make The tapered pin Pin is fitted to tapered hole. Excess is trimmed off.
  107. 107. Schematic representation of final prosthesis
  108. 108. Connectors for all ceramic fpd’s “Stress concentration in all-ceramic posterior F.P.D” Qint .int 27(10),701-706 Material Diameter of connector Maximum stress Gold 3mm 20.5 4mm 12.7 Dicor 3mm 19.4 4mm 12.5 Inceram 3mm 12.5 4mm 7.0
  109. 109. • It was found that stress concentration was found more in region of force applied and at connector region. • stress levels were higher in 3.0mm than in 4.00 mm at connector.
  110. 110. • Higher stress was found in the apical region of connector & least in middle part of connector. So they advised to increase the height of connector to increase the bulk and have good stress distribution, and have smooth geometry as compared to angulated geometry in short connectors. • It was recommended to use 4mm connector size for ceramic and 3mm for metal.
  111. 111. Photoelastic stress analysis of load transfers to implants and natural teeth comparing rigid and semirigid connectors.J.Prosthet Dent 1999;81:696-703 • Use of soldered or rigid connector between implants and simulated tooth abutments promote favourable stress distribution within simulated bone support.
  112. 112. • Although rigid and non-rigid connectors may allow favourable stress distribution, non rigid connector may not be indicated because of unpredictable mobility and intrusion. • Hence rigid connectors should be used.
  113. 113. • Connecting teeth to osseointegrated implants presents a biomechanical challenge. This is due to the implant being rigidly fixed to the bone and the tooth being attached to the bone with a periodontal ligament. BRITISH DENTAL JOURNAL VOLUME 201 NO. 10 NOV 25 2006
  114. 114. • Diagram of the suggested method of connecting implants to teeth with connection using a deep removable partial denture- type rest with the rest seat on the implant supported restoration.
  115. 115. Intra coronal precision attachments • Herman Chayes – 1906 first designed • It consists of two parts A slot and a flange The flange is joined to one section of the prosthesis and slot unit embedded in a restoration forms part of another section
  116. 116. • The retention of attachment mainly depends on surface area of contact between two parts • Surface area is a product of cross section of male part and its length • The H-shaped flange of modern attachment provides greater surface area without increase in size of female part over earlier T-shaped flange
  117. 117. • Materials used in attachment fabrication: a. Platinum b. Iridioplatinum c. Au and Pt d. Au and Pd e. All gold Choice of material depends upon type of case
  118. 118. • When ceramometal alloys are employed , it is necessary to solder female portion into crown if any of the above materials are used except gold • Other materials will cause contraction and distortion of the attachment during porcelain firing • Gold can be used for insertion into cast gold crown only
  119. 119. • Precious metal attachments should never be cast to non precious alloys , it may result in recrystallisation of the attachment and produces an incomplete casting • Intra coronal attachments are discussed as 1.Frictional fit with adjustment potential 2. Frictional fit without adjustment potential
  120. 120. • Without adjustment potential: 1. Interlock attachments 2. Stern JMS attachments 3. Beyeler attachments 4. Chayes attachments • With adjustment potential: 1. Mc Collum attachment 2. Stern G/A attachment
  121. 121. 3. Chrismani attachment 4. Stern gingival latch attachment
  122. 122. Chayes attachmentBeyeler attachment
  123. 123. T-Geschiebe 123 attachment Stern gingival attachment
  124. 124. Conclusion
  125. 125. • The prognosis of an fixed partial denture will depend on occlusion, span length, bone loss and quality of periodontium. Since majority of stress are concentrated at the connector area of the fixed partial denture, they have to be precisely made. Connector should be large enough so that it can resist the forces and at a same time it should be aesthetically pleasing and should be in harmony with embrassure space.
  126. 126. References
  127. 127. • Fundamentals of fixed prosthodontics- Shillingburg • Contemporary fixed prosthodontics- Rosenstiel • Ceramo-Metal technology.Vol.1 Masahiro Kuwata • IJP 1993;6;468-74 • DCNA , vol24,no.1,jan 1980 • Precision attachments: Harold Prieskel vol.1
  128. 128. • BRITISH DENTAL JOURNAL VOLUME 201 NO. 10 NOV 25 2006 • J.Prosthet Dent 1999;81:696-703 • IJP2000, 13,340-346 • j.prosthet dent 76(4) 424 1996 • Operative dentistry,1994,19,7-10 • Precision attachments: A link to successive restorative treatment-Gareth jenkins
  129. 129. • Non-rigid connectors in fixed prosthodontics:current concepts and case reports.JIPS2005;5:2,99-102
  130. 130. For more details please visit