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Wax patterns fabrication for fixed partial dentures

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wax patterns in fpd

Text of Wax patterns fabrication for fixed partial dentures

  • 1. CONTENTS Introduction Prerequisites Material sciences Technique Armamentarium Waxing instruments Posterior teeth Anterior teeth Waxing for metal ceramic crowns. Conclusion

2. INTRODUCTION Lost wax technique metal prosthesis.Success in clinical practise depends upon on everystep in the treatment procedure. A large of percentage of time and effort spent infabricating fixed prosthesis is devoted toproducing a very accurate pattern. 3. Most defects can be easily be corrected in waxpattern but cannot be done in a metal casting. Follow:-1. Precise technique,2. Use the correct armamentarium3. Handle the material(wax) carefully in order toobtain 4. Prerequisites for wax patterns1. Correction of defects. Small defects on the die like dimples due to caries orloss of previous restorations Normally blocked out intraoral by GIC Can be blocked on the die as long as the defect doesnot extend to within 1 mm of the cavity margin. Blocked out using zinc phosphate cement Autopolymerizing resin, monomer spray etc 5. 2. Provision of adequate cement space. Adequate cement space is of 20 to 40 um for each wall. So internal diameter of the wall of crown would be 40 to80 um. 1mm of band around the margin shouldnt be given anyluting space. If no luting space is provided the crown wouldnt seatcompletely due to the hydraulic pressure from the viscouscement. 6. Die spacer is most commonly used to create space for the lutingcement. This material (similar to model airplane paint) is applied to thedie to increase the cement space between axial walls of theprepared tooth and the restoration. It is formulated to maintainconstant thickness when painted on the die. Different types of die spacers are:- Red, 7 microns: Yellow, 7 microns Blue, 10 microns New dentin, 10 microns Gold 13 microns Silver, 13 microns 7. 3. Marking the margins The margins should be marked in order to locate it during waxcarving. It should be dileneated with a contrast coloured pencil like redfor green wax. Graphite pencil shouldnt be used as it can abrade the die andalso act as antiflux. If required the marked area can be coated with a thin layer ofcyanoacrylate. 8. Material science GC inlaywaxes Cornings inlay waxes Bego inlay waxes Kemdent inlay waxes Kerr inlay waxes Charminar inlay waxes 9. Material scienceComposition of inlay wax Paraffin-60% (Melting range 40-71o C) Carnauba-25%(Melting range84-91o C) Beeswax-5% Ceresin-10% Natural resins (gum dammer)-less than 1% Organic fillers- added to avoidexcessive shrinkage, expansiondue to temp change Microcrystalline wax- Inminute amount. Candelilla Coloring agents 10. According to ADA no 4 it is of two types:- Type I-a medium wax (generally used with the directtechnique for making patterns in the oral cavity) Type II-a softer wax (generally used for the indirectfabrication of castings) Waxes used with direct techniques must not flowappreciably at mouth temperature. Those used with indirect techniques must resistflow at room temperature to maintain their newlyshaped forms.Source:- Philips textbook of dental materials 11. Points to be followed while using waxes:- Its has ELASTIC MEMORY should be thoroughly liquefiedbefore it is added to die, dipping method is best. STRESS RELEASE as wax sets stresses are released. HIGH THERMAL EXPANSION AND CONTRACTION so itshould be heated only adequately. So because of above properties the wax patterns should beremelted at the margins before it is invested for properadaptation. 12. Different types of waxes used:- Special wax for electrical wax heating unit(vario therm), Dark blue-hard and light blue soft are formodelling, trimming and dippingapplication, Lilac-medium hard , red stress free forcervical margins, Green wax-hard for trimming. Dip application yellow wax caps of uniformstrength Wax Preforms are available - It simplifieswax up and shorten finishing procedure 13. Different techniques in wax pattern fabrication:1. Dipping method.2. Addition method.3. Molten press method.4. Injection method.Source:- Google Web 14. Armamentarium required for wax pattern fabrication1. PKT waxing instruments2. No 7 wax spatula3. Laboratory knife with no 25 blade4. Sharp colored pencil (contrasting to wax)5. Sable brush6. Bunsen burner/electric wax knife7. Inlay wax8. Occlusal indicator powder(zinc-sterate or powderedwax)9. Die spacer10. Die lubricant (separating liquid)11. Soft tooth brush12. Fine nylon hose 15. Waxing instruments:- Waxing instruments can be categorized by the intent of theirdesign:1. Wax addition,2. Carving, or3. Burnishing. Of the popular PKTs (designed by Dr. Peter K. Thomasspecifically for the additive waxing technique), No. 1 and no. 2 are wax addition instruments, No. 3 is a burnisher for refining occlusal anatomy, Nos. 4 and 5 are wax carvers. 16. No1 & 2No 3 No 4No 5No 7 17. Wax carvers. No. 2 Ward and nos./, and 3Hollenback.DPT no. 6 wax burnisher.Electric waxing instrument 18. Sequence in wax pattern fabrication1. Coping fabrication.2. Wax pattern removal and evaluation.3. Proximal surfaces.4. Axial surfaces.5. Occlusal surfaces.6. Margin finishing. 19. 1. Coping fabricationa) Before coping is fabricated dielubricant is applied.b) The wax is added PKT no1 or no 2.c) Initial layer should be completelymolten Memory effect!!!!!d) Whenever subsequent layers of waxare added the previous layer whichwas applied should be remelted or elsecreases or folds would form on fittingsurface.e) A large waxing instrument can be usedlike PKT no 7 is adequate for thispurpose. 20. f) Adequate bulk should be providedat proximal and axial surface inorder to prevent distortion whileremoval.g) Excess wax at the margins shouldbe scrapped of carefully.h) Thin layers scrapping----carefully-----damage to the die---use burnisher instead of sharpcarvers.i) Dipping the die in molten wax potis easiest and better way tofabricate a coping. 21. 2. Wax pattern removal andevaluation The wax pattern sufficiently cooled Removed using the thumb and forefingerwith light grip pressure. A small rubber dam piece. If the pattern is not coming out theexcess wax at the margin should betrimmed of. After it remove the patterns is evaluated 22. 3. Proximal surfaces The proximal surfaces of natural teeth tend to be flat orslightly concave from the contact area to the cementoenameljunction, and any restoration must reproduce this feature. Over contouring maintaining periodontal health difficult Excessively concave or under contoured proximal surfaces flossing ineffective.Proximal area gingivaltoThe contact area areNormally flat or concave 23. Contact areas:- Abnormally large proximal contact make plaquecontrol more difficult can lead to periodontal disease Very small (point) contacts may be unstable and causedrifting Deficient contacts can also lead to food impactionOn maxillary teeth moreOcclusal and buccal whenProgressing anteriorlyOn mandibularposterior teethCentrally located 24. Procedure:- The wax coping is seated back on to the die Wax is added coping at the contact area dieis seated back with wax is in molten state. After the wax is hardened the die is removed andthe wax gingival to the contact area is shapedaccordingly. The proximal surface is evaluated and the surfaceshould be either flat or slightly concave. They should adequate space for the lingual andbuccal embrasure. The wax should continue to the unprepared toothsurface. 25. Axialsurfaces:- The buccal and lingual surfaces are shaped to followthe contours of adjacent teeth. The height contour should be adequately placedusually at the gingival third of all the teeth except inmandibular molars it is present in the middle third. The natural teeth are rarely more than 1mm wider attheir height of contour than at CEJ 26. The tooth surface gingival to its height of contourimmediately adjacent to the gingival soft tissues iscalled emergence profile, it is usually flat orconcave. Straight profile treatment objective Creation of convexity or a shelf or ledgebacterial plaque removal difficult to causeinflammation of marginal gingiva. Special care should be taken when waxing teethwith recession or exposure of furcation, providingadequate space for hygiene procedures 27. Procedure:- Adjacent and contralateral teeth are used as guide A flat profile is created gingivally . No change of direction from unprepared toothstructure to axial restoration contour Add wax to join axial and proximal surfaces andsmooth them, the line angles should correspond tothose on contralateral teeth if present 28. Evaluation:- Evaluate at greatest convexity Compare with contralateral tooth Each part of the outline is scrutinizedproperly. Buccal and lingual contours and theembrasures should all be assessed. Each contact area has fourembrasures: gingival, buccal, lingualand occlusal, except occlusal all willbe complete by now All the embrasure should besymmetrical. 29. Occlusal surfaces:- The cusps and ridges of the occlusal surfacesshould be shaped to allow even contact with theopposing teeth while stabilizing the teeth anddirecting forces along their long axes. Non-functional cusps should provide adequatehorizontal and vertical overlap. 30. Why put all those grooves on the occlusalsurface???? Why not simple inclined planes on a flattable???? 31. Numerous occlusal contacts Small centric contacts allow fordisclusion in excursionOcclusal morphology with inclined planeproduceLarge contacts in centric occlusion A and inExcursions B 32. Importance of OcclusalMorphology Point contacts between opposing teeth are preferredto broad, flat occlusal contacts because1. Wear of the restorations will be minimized and2. Mastication of tough or fibrous foods improved. 33. Effect of anterior guidance The contact of anterior teeth in excursions affects the movements ofthe mandible Change in morphologic features of anterior restoration can changethe anterior guidanceIncrease in v

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