Connectors in fixed prosthodontics

Connectors in fixed prosthodontics

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  Noreen Mohammed NaguibMosaad 5212322 G.11 Connectors in fixed prosthodontics
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  To stress-break ornotto stress-break, thatis the question!! Maxillary FPD Anterior : fixed Posterior : fixed-free Mandibular FPD Anterior : Fixed Posterior : Fixed-free i.e. Fixed at the posterior connector and stressbroken atthe anterior connector. Now, it is becoming more common to stress break ALL POSTERIOR BRIDGE The occlusalforcesapplied to a fixed partialdenture (FPD) are transmitted to the supporting structuresthroughthe pontic, the
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  connectors, and theretainers. Variablesthat may influence the longevity of a bridge and its abutmentsinclude the occlusion, span length, bone loss, and the quality of periodontium. The excessive flexing of the long-span FPD, which varieswith the length of the span cubed, can lead to materialfailure of the prosthesis or to an unfavorable tissue/bone response. Biomechanicalfactorssuch as occlusaloverload, leverage, torque, and flexing, induce abnormalstressconcentration in an FPD. This stress concentration isfound in the connectorsof the bridge and in the cervical dentin area near the edentulousridge. This factor playsan importantrole in the potentialfor failure, particularly in long-span bridge. Remember that connectorsare thatportion of the bridge thatunites the retainersand the pontics. They are of two types, rigid connectorsand non-rigid connectors(NRCs). Rigid connector could be made by casting, soldering, and welding. The cast connectorsshould be properly shaped in waxpatterns. The soldered connectorsare made by fusion of an intermediate metal alloy to the previously made castings. These days, the one piece casting goes a long way towardsovercoming rigid connector failure in bridgework. The connector thatpermitslimited movementbetween the otherwise
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  rigid membersof theFPDs, is the Non- Rigid Connector or NCR. The NRC could be made by an incorporation of prefabricated precision inserts, by use of a custom-milling machine or by use of the prefabricated plastic patterns. Ref. Pissiotis AL, MichalakisKX. An esthetic and hygienic approach to the use of intracoronalattachmentsasinterlocksin fixed prosthodontics. J Prosthet Dent Non-rigid conncetors
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  The indicationsfor theuse of the NRC in fixed prosthodonticsare : 1. The existence of a Pier abutment, which promotesa fulcrum-like situation that can cause the weakest of the terminalabutmentsto fail and may also cause intrusion of the pier abutment. But should Pier Abutmentsbe used at all considering their high failure rate ??? (Ziada et al. 1998.) 2. The existence of a malaligned abutment, where parallelling preparationsmightresultin excessive tooth preparation and devitalisation. Such situations can be solved through the use of intracoronalattachmentsasconnectors. 3. The presence of mobile teeth , which need to be splinted together with the fixed prosthesis. In such situations, it is not practicalto cementa splinting type restoration with numerousteeth involved. Through the use of interlocks, smaller segments can be cemented with the splinting effectprovided by the interlocks
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  4. Long spanFPDs: which can distort due to shrinkage and pullof porcelain on thin sections of framework and thusaffectthe fitting of the prosthesison the teeth. Again, should long span bridgesbe favored considering their failure rate and considering the success rate of implants ??? 5. In situations where a questionable distal abutmentexists and fabrication of the fixed partialdenture is considered to be the best interim treatment, the use of the NRC may solve the problem of not having to repeatthe restoration of the remaining abutment(s) after final failure of the questionable abutment. 6. It could also be used with osseointegrated implants. So, the NRCs are mainly used to reduce stress on the abutmentand to accommodate malaligned FPD abutments. The four typesof NRCs are the 1. Dovetail (key-keyway)or (Tenon-Mortise) connectors. 2. Loop connectors. 3. Split connectors. 4. Cross pin and wing connectors. Align the path of the keyway to thatof the mesial abutment. A deep wax boxis carved into the distal of the waxpattern for the incorporation of a keyway, which in turn requiresan intracoronal preparation of adequate depth and a parallelpath of insertion.
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  Ref: Badwalk PV,Pakhan AJ. Non-rigid connectorsin Fixed Prosthodontics: currentconcepts. J Indian DentAssoc. 2005;5:2,99-102 Banjaree S. et al Non-rigid connectors- the wand to reduce stresseson the abutmentteeth. Contemp Clin Dent2011,2:351. Sutherland etal. (1980) suggested thata rigid bridge resolves more of its stress internally before the remaining stress can reach the bone, and it has been found thatthe greatest stress concentrationsin a rigid bridge occur in the connectors.With a non-rigid design, the stress may be directed through the abutmentteeth to the supporting bone rather than being concentrated in the connector itself. _ This meansthat the prosthetic material and the luting cementin a rigid design must withstand much greater stress than in the non-rigid design. Another problem thatexists in the posterior mouth is the inequality of the abutmenttooth size. _ In a bridge replacing a first molar for example, the smaller abutment(second premolar) may develop a thicker pericemental cushion following frequentstress, as a compensating measure for this stress. As a result, weaker abutmentsmay move more than the larger sturdier abutment. Thisresults in large lever strains on the weaker abutmentwhich tendsto shear the luting bond.
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  _ However, whena stress-breaker isused on the smaller abutment, it will tend to dissipate much of the leverage force. _ Stress-breakerscan also be required in long-span bridgesas satisfactory tooth alignmentbecomesmore difficult to achieve. _ Even in short-span bridgeswith divergentabutmentteeth, abutmentpreparationsdo nothave to be parallelto each other. Each preparationscan be designed to MAXIMIZEindividual retention, independentof a common path of insertion. The use of stress-breakersalso tends to break up bridge length to more manageable portionsand makessubsequentrepair/replacementeasier. Fixed-fixed Rigid connectors