Partial Dentures
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What are examples of partial denture alloys?
Type IV Gold Co-Cr Titanium
What YM and EL is wanted for partial denture bases?
Base : high YM - to maintain shape in use high EL - to avoid plastic deformation
What YM and EL is wanted for partial denture clasps?
Clasp : lower YM - to allow flexure over tooth high EL - maintain elasticity over wide range of movement (ie strain)
What type of gold are used for partial denture?
Type 4
How is the heat treatment of gold alloys done?
• Quench after casting to create fine grains • Anneal to homogenise • If cold working has been done, stress relief anneal • Heat harden
What are the properties of gold alloy more suitable for? Clasp or Base?
properties more suitable for clasp need thickness for base (expense) Gold IV alloys have a higher elastic limit and reduced rigidity, meaning they can endure more elastic deformation and easily flex over the tooth.
What is the effect of nickel in CrCo?
replaces some Co improves ductility slight reduction in strength
What is the hardness of CoCr? And what is it better than?
BHN 370 much harder than Gold
Compare gold and CoCr
• Co-Cr has greater shrinkage and is less ductile (Elongation %) compared to Au IV. • Co-Cr is less dense and has a higher YM (rigidity) and Hardness compared to Au IV. • The Compressive strength of Au IV and Co-Cr is similar.
What partial denture alloy has the best ductility?
titanium (CrCo low ductility)
What PDA has the best UTS?
stainless steel
What PDA has the best density?
gold
What PDA has the highest hardness and ridgity (YM)?
cobalt chrome
What PDA shrinks the most?
cobalt chrome
What are advantages of using titanium?
Good biocompatibility Good corrosion resistance (passive oxide layer) Parts joined by laser welding