Materials for Crown & Bridge and Cast Partials

1. Materials for Crown & Bridge and Cast Partials DHYG 113 Restorative Dentistry I

2. Objectives • Discuss the factors that affect treatment planning for fixed indirect restorations • Explain the lost wax casting process • Describe the types of alloys used to fabricate all-metal crowns, ceramometal crowns, and partial denture frameworks • Discuss the types of porcelain used to simulate natural tooth color • List the advantages and disadvantages of all-metal, ceramometal, and all-ceramic restorations

3. Indirect Restorations • Constructed outside the mouth • Inlays– intracoronal, do not cover cusps • Onlays– restore cusps and entire occlusal • Crowns – cover entire tooth • Complex restorations– combination of features of inlay, onlay, and crown • Bridge– replaces missing teeth • Retainers (abutments) on each end with pontic(s) replacements

4. Crowns

5. Classification by Material • Metals • Ceramics • Ceramometal – porcelain fused to metal(PFM) • Composites – cured at elevated temperatures, pressures, or both • Fiber reinforced composites are much tougher and stronger than particle reinforced composite materials

6. Gold

7. Constructing Indirect Restorations • Diagnosis • Treatment Plan • Periodontal status • Endodontic status • Caries risk • Adequate tooth structure (buildups)

8. Indirect Restoration • Restoration Design • Esthetic considerations • Attrition • Biocompatibility • Location of margins • Diagnostic waxup

9. Indirect Restoration • Preparation – tooth reduction • Impressions (see Ch. 8) • Fabrication of Temporary Restorations • Preparation – tooth reduction

10. Laboratory Procedures • Lab Prescription • Impressions disinfected and poured (in the office or at the lab) • Lab constructs final restoration per the dentist’s instructions

11. Case Study http://portal.daledental.com/files/proddocs/41/Captek%20Chairside%20by%20Ross%20Nash.pdf

12. Cementation of the Restoration • Temporary is removed and cement cleaned off prepared tooth • Final restoration is assessed • Proximal contacts • Margins • Occlusion • Esthetics • Restoration is cemented

13. Completion of the Treatment Plan • What’s next? • Recall status based on caries risk, perio health, etc.

14. Waxing • Wax is heated and shaped to the form of the restorations

15. Dental Waxes • Inlay wax • Used for casting restorations • Burns away completely • Hard, high melting temp. • Not sticky to touch • Sticky wax • Hard wax w/ high melting point • “sticks” well when cooled • Baseplate wax • Boxing wax and rope wax • http://www.dentalmatic.com/waxpro_B2.htm

16. Investing and Investments • Procedures • Requires a mold space into which molten metal flows • Mold space made by embedding the wax pattern in a mold material • Sprue is attached to the wax pattern • Wax pattern is attached to the sprue base Attaching the sprue

17. Investment Materials • Gypsum-based products • Silica added to improve heat resistance • Increases thermal expansion to compensate for metal shrinkage • Different investment materials have different expansion characteristics

18. Burnout

19. Burnout • Temperature controlled oven used to burn out wax pattern from investment • Casting ring placed in oven and mold heated to 500 - 600ºC • Wax melts leaving clean mold space • Casting left in oven for ~30 minutes to “heat soak” the ring, ensuring burnout

20. Casting • Involves melting the casting alloy & forcing it into the mold space • Gold casting alloys easily melted with “blow torch” using compressed air and natural gas or propane • Metal is melted in ceramic crucible

21. Casting Process • Lost wax casting technique • Restoration is constructed out of wax • Wax is replaced by metal Melting the metal

22. Casting • Centrifugal casting machine most common • Centrifugal force • Spins molten metal • Liquid metal forced to flow into the mold • Metal cools, casting is complete Vacuum air-pressed casting machine

23. Divesting, Finishing, Polishing • Casting is retrieved from the ring • Sprue and button are cut off the restoration • Casting is cleaned in an acidic solution (pickling) • Restoration placed on die and polished using a variety of abrasives • Final polish with Rouge • www.brookestonejewelry.com/links.htm

24. Alloys for All-Metal Restorations • Traditionally gold alloys • Pure gold is too soft • Gold (75% by weight) is combined with copper (~5%), silver (~10%), palladium (~2%), zinc (~1%), and other elements to form high-noble dental alloys • Gold alloys are easily cast with gypsum-bonded investment and simple equipment

25. Properties of Casting Alloys • Performance criteria for: • Strength • Elongation – measure of ability to burnish margins of a restoration toward the tooth • Tarnish • Biocompatibility

26. ADA Classification • Type I – weakest • Type II • Type III • Type IV – strongest, least elongation • Used for high-stress bridges and partial denture frameworks

27. Noble Metals • Gold • Platinum • Palladium • Other inert metals • Precious metals: classified based on cost. • Includes noble metals and silver

28. Classification by Gold Content • Percent is parts per 100 • Carat is parts per 24 • Fineness is parts per 1000 75% = 18 carat = 750 fineness

29. Classification by Composition • High gold or high-noble alloys contain 60% or more gold and other noble elements • They are usually yellow metals • Silver-palladium alloys: ~70% silver and ~25% palladium • They are usually white in color • Low-gold – contain at least 25% noble metals with gold replaced by silver • Usually yellow or white • Base metals -- less than 25% noble elements Nonprecious – no noble elements

30. Alloys for Ceramometal Restorations • Metal casting must withstand porcelain firing temperatures • Bonding porcelain requires temperatures much higher than melting point of alloys for all-metal restorations • Metal substructure (coping) is waxed and cast, then cleaned (pickled) • Metal is oxidized by heating in porcelain oven (tin, indium, gallium added to alloys)

31. Porcelain • Porcelain powder is applied in layers to simulate layers of teeth • First layer hides the metal (opaque) • Second layer – bulk (body) • Enamel layer (translucent) • Each layer may be fired separately or in combination – 850 - 1100ºC • Typically involves 3-5 firings

32. Ceramometal Alloys • Noble alloys: Gold (~88%), platinum (~4%), palladium (~6%) – yellow in color • Gold (~50%), palladium (~40%) – white • Noble alloys of choice today • Palladium (~60%), silver (~30%) – cheaper • Non-precious alloys – Nickel (~80%), chromium (~10%) – white, stronger & harder than noble alloys, cheaper • Chromium (~65%), cobalt (~25%) – white and inexpensive. Highest melting point and most difficult to cast

33. Titanium • Material of choice for dental implants • The most biocompatible metal

34. Partial Denture Frameworks • Nickel-chromium and cobalt-chromium alloys were adapted from similar materials used in aerospace industry • High melting temperatures use slightly different casting techniques • Silicate and Phosphate-bonded investments – withstand higher burnout temperatures compared to gypsum-bonded investments – harder to use

35. All-Ceramic Restorations • Porcelain jacket crowns • Entire crown made of porcelain by applying porcelain powders to a thin layer of platinum foil on the die

36. Strengthening Ceramic Materials • Ceramometal – porcelain bonded to metal (PFM) • Advantages • Precise fit • Tough mechanical properties • Disadvantages • Opaque to light • Not as natural in appearance as all-porcelain crowns