Connectors in fpd / dental continuing education


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Connectors in fpd / dental continuing education

  1. 1. Connectors in FPD INDIAN DENTAL ACADEMY Leader in continuing dental education
  2. 2. Contents • Introduction • Types of connectors – Rigid&Nonrigid • Types of Rigid connectors • Types of Nonrigid connectors • Connector design • Heat sources for soldering • Step by step procedure-Soldering • Conclusion • Bibliography
  3. 3. Connector is that part of a Fixed Partial Denture (FPD) that joins the individual components(pontics and retainers) together.
  4. 4. This can be accomplished by • Rigid connectors • Non rigid connectors
  5. 5. Rigid connectors can be made by Casting - shaped in wax Soldering - intermediate metal alloy Welding - joining with heat
  6. 6. Non Rigid Connectors Any connector that permits Limited Movement between otherwise independent members of F.P.D
  7. 7.
  9. 9. Cast Connectors • Cast Connectors are shaped in wax as part of a multiunit wax pattern.
  10. 10. Advantages • Cast connectors are convenient and minimize the number of steps involved in the laboratory fabrication.
  11. 11. Disadvantages • The fit of the individual retainers may be adversely affected because distortion occurs more easily when a multiunit wax pattern is removed from the die system.
  12. 12. Restrict cast connectors to • Complete coverage restorations which can be gripped buccolingually.
  13. 13. Soldered Connectors • Soldering is used to describe most metal joining process that involve the flow of a filler metal between two or more metal components
  14. 14. • Here the use of an intermediate metal alloy is used whose melting temperature is lower than that of the parent metal
  15. 15. • Connectors to be soldered are waxed to final shape and sectioned with a thin ribbon saw. • So that when the components are cast, the surfaces to be joined will be flat,parallel, and a controlled distance apart. • This ensures accurate soldering with a minimum of distortion.
  16. 16. Ribbon saw
  17. 17. SOLDERING GAP WIDTH:- • The liquid solder is drawn into the joint through capillary action • Thus an optimum gap is necessary for proper flow and strength of the joint and to avoid distortion of the assembly • Gap width ranging from 0.13 to 0.3 have been suggested as optimum
  18. 18. LOOP CONNECTORS:- Existing diastema
  19. 19. Loop on the lingual aspect of the prosthesis that connects adjacent retainers and /or pontics
  20. 20. Welding Connectors • is another method of rigidly joining metal parts. • The joining of two or more metal pieces by applying heat,pressure or both ,without a filler metal ,to produce a localized union across the interface.
  21. 21. • Can be done by Spot welding by passing of electric current • Laser Welding based on a pulsed high power neodymium laser with a very high power density.
  22. 22. • The units consists of a small type of glove box that contains the laser tip, an argon gas source, and a stereomicroscope with lens crosshairs for precise alignment of the laser beam with the components. • The maximum penetration depth of these laser welding units is 2.5 mm.
  23. 23. • Since only a small amount of heat is generated, the parts can be hand-held during the welding procedure. • Welding can be performed close to ceramic or resin veneers without causing damage to these materials.
  25. 25. Non rigid connectors Indications 1. When it is not possible to prepare two abutments for an FPD with a common path of placement. 2. Segmenting large, complex FPDs into shorter components that are easier to replace or repair individually.
  26. 26. 3. Pier abutment
  27. 27. 4.Mal aligned abutment Difficult to prepare along long axis - might result in devitalisation
  28. 28. 5.Questionable distal abutment- only a portion of the FPD may be remade.
  29. 29. Used to • Relieve stress • Accommodate malaligned FPD abutments • FPD with anterior & posterior segments • Abutments with uncertain prognosis
  30. 30. • During the mandibular opening and closing stroke, the mandible flexes mediolaterally. • Rigid fixed partial dentures have been shown to inhibit mandibular flexure and extensive splints have been shown to flex during forced
  31. 31. • The associated stresses can cause dislodgement of complex FPD’s. • Segmenting complex mandibular FPD's can minimize this risk . • Hence Non rigid connectors are favorable here.
  32. 32. Types of Non Rigid Connectors • Dovetail (Key – Keyway) • Split pontic(connector inside the pontic) • Cross Pin & Wing
  33. 33. Dovetail (Key – Keyway) • Align Path of insertion of the keyway with that of the distal abutment
  34. 34. Pontic Deep wax box- distal surface Of wax pattern Mortise/Female /Keyway
  35. 35. A- the mesial segment ,with the keyway,is cemented first B- the distal segment ,with the key ,is cemented immediately after A B distal aspect of the anterior retainer
  36. 36. Mortise can be prepared by • Incorporation of prefabricated inserts • Wax Patterns • Custom milling • Prefabricated plastic patterns Pulp size and clinical crown height can be limiting factors in the design of non rigid connectors
  37. 37. •Prefabricated plastic patterns
  38. 38. Split Pontic • This is an attachment that is placed entirely within the pontic • Useful in tilted abutment cases where the use of of a conventional dovetail would require the preparation of a very drastic box.
  39. 39. A B A- The mesial segment , has a distal shoe that is the gingival portion of the pontic B- The distal segment covers the mesiogingival part of the pontic
  40. 40. Cross pin and Wing These are the working elements of a two piece pontic system This allows the two segments to be rigidly fixed after the retainers have been cemented
  41. 41. •A-The distal retainer and wing are cemented first •B- The retainer and pontic is seated last A B
  42. 42. •A tapered pin is driven through the pontic ,the wing and back out from pontic
  43. 43. • Used primarily in accommodating abutment teeth with disparate long axis • The path of insertion of each tooth is made parallel
  45. 45. • The size, shape, and position of connectors all influence the success of the prosthesis. • Adequate access ( i.e. Embrasure space) must be available for oral hygiene aids cervical to the connector.
  46. 46. • Connectors must be sufficiently large to prevent distortion or fracture during function • But not too large otherwise, it will interfere with effective plaque control and contribute to periodontal breakdown over time.
  47. 47. • Metal-ceramic fixed partial dentures are usually fabricated as a single unit, sometimes it is necessary to solder the units together.
  48. 48. This may occur if 1.There is distortion in a single- piece fixed partial denture casting 2.One retainer has inadequate margins and must be redone 3. The FPD length is too great for an accurate single-piece casting
  49. 49. PRECERAMIC SOLDERING • Preveneer soldering uses a high-fusing solder that is melted by torch before porcelain is added.
  50. 50. • Once a metal – ceramic framework has been assembled by Pre ceramic soldering, the subsequent procedures are the same as if it had been cast in one piece.
  51. 51. Advantages • Allows the connected prosthesis to be tried in the mouth in the unglazed state & any necessary adjustments can be made to the porcelain.
  52. 52. Disadvantages • Having to apply the porcelain to a longer structure which needs support • It is also difficult to contour the proximal embrasures so that the units look like natural teeth.
  53. 53. Post Ceramic Soldering In post veneer soldering,a low-fusing solder is melted in the oven after porcelain has been baked on the fixed partial denture.
  54. 54. Post ceramic soldering compensates for any tooth movement in the mouth between final impression and restoration and it eliminates the significance of any distortion that might occur during porcelain firing.
  55. 55. • All porcelain adjustment and firing must be completed before soldering. • The proximal areas are shaped before soldering, therefore it looks more natural than a presoldered or cast connector.
  56. 56. SOLDERING ALL- METAL FPD's:- Soldering such retainers permits the retainers to be shaped and adjusted individually with improved access for finishing procedures.
  57. 57. • Advantage-Soldering simplifies that manipulation of wax patterns. • Disadvantage -it requires an additional step, compared to a one- piece casting.
  58. 58. Staffanou et al Strength properties of soldered joints from various ceramic metal combinations JPD1980 • Staffanou et al in found that 20 % of post ceramic soldered joints involving base metal alloys had to be resoldered because they were so weak that they broke with finger pressure.
  59. 59. Anusavice et al :flexure test evaluation of presoldered base metal alloys JPD1985 • Anusavice et al showed great variability in solder joint quality with these alloys , with no consistent relationship of strength to gap width.
  60. 60. • These authors found that most failures occurred through the solder and were attributable to voids caused by gas entrapment or localized shrinkage.
  61. 61. Fehling et al Cast connectors :an alternative to soldering JPD1987 • However, because of the problems of soldering base metal alloys, various alternative procedures have been advocated. • These include making the soldered joint through the center of the pontic to increase the area soldered.
  62. 62. • Another alternative is connecting the parts by a second casting procedure with the molten metal flowing into undercuts in the sectioned pontic.
  63. 63. Cast Joining • A process of joining two components of a FPD by means of casting molten metal into interlocking region between the invested components . • This procedure is sometimes preferred for base metal alloys because of technique sensitivity
  64. 64. • This was proposed by Weiss and Munyon (1980) as an alternative method for joining cast components of FPD • Cast joined components are held together purely by mechanical retention
  65. 65. Heat Sources for Soldering
  66. 66. Torch Soldering Portion of flame used for soldering should be neutral or slightly reducing because this produces the most efficient burning process and most heat .
  67. 67.
  68. 68. • The flame should never concentrated in one area but kept in constant motion to prevent uneven heat application ,which could result in fracture.
  69. 69. • Some researchers believe the flow of solder is more controllable during torch soldering because a slight temperature differential can be created and the solder always flows toward the hotter point .
  70. 70. OVEN SOLDERING Furnace or Oven soldering is performed under vacuum or in air. A piece of solder is placed at the joint space and the casting and solder are heated simultaneously.
  71. 71. • The method does not allow the moment of the solder fusion to be observed. • This may be important, because the longer the solder remains molten, the more it will dissolve the parent metal and consequently weaken the joint
  72. 72. • In the porcelain furnace the soldering assembly is heated above the fusion point of the solder, the muffle door is opened , and the solder is fed into the joint space. • Some furnaces have a observation window
  73. 73. INFRARED SOLDERING A specially designed unit that uses an infrared energy from a tungsten iodine lamp that operates at 3400 C
  74. 74. The operator observes the soldering procedure through a dark screen and cuts off the electrical supply when solder flow is observed
  75. 75. • Good accuracy is possible with the system. • It requires more time than conventional soldering . • The joints have similar strength to conventional soldering.
  76. 76.
  77. 77. LASER WELDING • Laser Energy is extensively used for welding in many industries and has been described in described in dentistry since the 1970s
  78. 78. • Laser assembly has reported higher strength and reduced corrosion in comparison to conventional soldering • Although laser welding does seem susceptible to fatigue failure.
  79. 79. • Laser welding may be a practical way to joint cast titanium components (e.g. if these are to be used for implant superstructures).
  81. 81. Sarfati E Harter et al – Comparative accuracy of FPD made as one piece castings or joined by solder IJP 1992 • Harter et al said that Controversy exists as to the relative accuracy of fixed partial dentures that are cast in one piece, preceramic soldered, or post ceramic soldered.
  82. 82. • The determining factor should be the fit of the individual abutment castings. • In some situations it may be impossible to cast a long- span FPD with ideal retainer dimensions and ideal interabutment dimensions
  83. 83. • In such circumstances a soldered connector may provide better accuracy.
  84. 84. • The situation is reversed when fabricating frame works for implant supported prostheses • An accurate, passively fitting implant superstructure is critical to avoid damaging forces.
  85. 85. Wee et al Strategies to achieve fit in implant Prosthodontics .IJP 1999 • However, Wee at al have said that it is not yet clear if accurate implant superstructure are most effectively made with one- piece castings or sectioned and soldered units.
  87. 87. ARMAMENTARIUM. Auto polymerizing acrylic resin. Zinc oxide- eugenol paste. Impression plaster Mixing bowl Spatula Small brush  Waxing instrument Sticky wax
  88. 88. Baseplate wax Sprue wax Soldering investment Glass slab Soldering tripod  Flux  Solder  Tongs .
  89. 89. Soldering Index
  90. 90. • Different methods can be used to record the required relationships of the parts to each other and to the abutment teeth and ridge tissues. • When FPD’s are assembled by soldering the relative position of the components is recorded with a Soldering Index on the
  91. 91. Advantages of an index • After the soldering procedure has been completed, the FPD can be reseated in the index and soldering accuracy can be verified
  92. 92.
  93. 93.
  94. 94. AUTOPOLYMERIZING RESIN SOLDERING INDEX:- • A Plaster Or ZnoE occlusal index is less suitable for the registration of anterior restorations. • The thinness of the incisal edges of these units makes them less stable, and accurate repositioning is more difficult.
  95. 95. • For this reason, auto polymerizing resin is recommended • The resin burns offs during the procedure. • A small brush dipped in resin monomer is touched to the polymer powder.This forms a bead . • The resin should extend onto the incisal edges of the
  96. 96. Step by Step Procedure
  97. 97. •Tongue depressor is soaked before using it to hold the index
  98. 98. •Plaster is troweled onto the tongue depressor to create a ridge that extends from one end of the index to another
  99. 99. •The seated index is stabilized over the FPD until the plaster sets
  100. 100. •Plaster index with components trapped in it
  101. 101. •Excess plaster around the FPD imprint is trimmed off with a sharp blade
  102. 102. •The trimmed index exhibits shallow imprints of the FPD components
  103. 103. •The gap width is measured by passing a business card
  104. 104. •When the two surfaces to be soldered are parallel ,there is less chances of distortion
  105. 105. •Wells are cut along the edges of the crown and pontic imprints to provide space for sticky wax
  106. 106. •The periphery of the plaster index is trimmed on the cast trimmer so that there will be a 3mm apron around imprint of the FPD
  107. 107. •Sticky wax is used in the wells to attach the FPD
  108. 108. •A triangular shaped piece of utility wax is extended facially and lingually .
  109. 109. •A strip of boxing wax 2.5 cm wide is wrapped around the index
  110. 110. Investment is brushed into the retainers
  111. 111. •After the investment has set ,the strip of boxing wax is removed from the index
  112. 112. •The index is pried loose from the block of investment
  113. 113. •The index is separated from the block of investment and inspected
  114. 114. •The Cast trimmer is used to remove excess height from the block of investment
  115. 115. •Buccal and lingual notches are carved in the investment
  116. 116. •Pencil marks are used as an antiflux on the occlusal surface of the castings
  117. 117. •Flux is placed in the solder joint area
  118. 118. •The invested casting is preheated over a Fisher burner for 10 to 15 mins
  119. 119. •The flame is directed against the investment from all sides
  120. 120. •Solder is placed into the lingual notch later into buccal notch
  121. 121. •When the solder in the joint appears to roll ,the flame is taken away
  122. 122. •The investment is removed after placing it in water
  123. 123. •Any remaining investment is removed with a sharp instrument
  124. 124. The finished solder joint
  125. 125. Evaluation • No solder should run onto the occlusal surface or cover the margins.
  126. 126. • The joints must be tested for strength any connector that can be broken by force of hand will not serve adequately in the mouth.
  127. 127. • Because broken connectors cannot be easily repaired interiorly once the prosthesis has been cemented. • The entire restoration usually must be remade.
  128. 128. Radiographic analysis of solder joint quality • When a FPD is delivered to the dental office its processing history is unknown • Of particular importance is the need to identify whether the FPD was cast in one piece or whether it was soldered or cast joined.
  129. 129. • For either soldered or cast joined structures, a radiographic examination of the joined area can be preformed • The simplest method is to lay the structure on a piece of Intraoral film and expose the film with a an X ray beam within accelerating voltage of 90 kV and a current of 10 mA for 1
  130. 130. • Another film should be exposed after rotating the FPD at a 90 0 angle to the initial orientation . • The flaws appear as radiolucent areas in presoldered connectors ,whereas the cast metal appears as a whole piece
  131. 131. SUMMARY and CONCLUSION
  132. 132. • Connectors join individual retainers and pontics. • Rigid or nonrigid connectors can be used. • Connector size,shape, and position influence the success of an FPD.
  133. 133. • The use of soldered connectors can simplify the fabrication of large fixed prostheses, which may be cast separately in groups of one or two units and assembled after their individual fit has been verified.
  134. 134. • All debris must be removed from the connector area because it interferes with surface wetting. • Heat sources used for soldering procedures include gas – air torches gas- oxygen torches, furnaces, infrared,
  135. 135. If the basic principles are understood and the technique has been mastered these procedures are entirely reliable.
  136. 136. References • Fundamentals of tooth preparation- 3rd edition Herbert Shillingburg • Tylman s Theory and Practice of Fixed Prosthodontics • Contemporary Fixed Prosthodontics- Rosenstiel 3rd edition • Fixed Prosthodontics- Keith Thayer • Johnston’s Modern Practice In Fixed Prosthodontics - Roland W Dykema • Science of dental materials - Anusavice
  137. 137. • Staffanou et al Strength properties of soldered joints from various ceramic metal combinations JPD 1980 • Anusavice et al :flexure test evaluation of presoldered base metal alloys JPD 1985 • Fehling et al Cast connectors :an alternative to soldering JPD 1987 • Sarfati E Harter et al – Comparative accuracy of FPD made as one piece castings or joined by solder IJP 1992 • Wee et al Strategies to achieve fit in implant Prosthodontics .IJP 1999
  138. 138. Thank you For more details please visit