Partial Denture Alloys
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what are the ideal properties of a partial denture alloy?
• rigid • strong • hard • ductile • precise casting • low density
what are the most common partial denture alloys used ?
• cobalt chromium - type IV gold
for a partial denture alloy base what is the ideal YM and EL?
High YM = to maintain shape in use High EL = to avoid plastic deformation
in a partial denture alloy clasp what is the ideal YM and EL values?
Lower YM = to allow flexure over tooth High EL = maintain elasticity over a wide range of movement
what type of cavities can pure gold be used for?
• Class III - Class IV
what occurs to the melting point of gold alloys if copper is the alloying element?
reduced melting point
how does alloying with copper affect the density of gold?
reduced density
what may occur to gold alloys if too much copper is added?
corrosion
what is an alloy used that is similar to platinum?
palladium (less expensive)
what are some uses for CoCr?
• cast partial dentures • wires • surgical implants
for CoCr partial denture connectors, explain the desirable EL & YM for the palatal/bulky section of connector?
• high EL - high YM
if CoCr is being used in partial denture clasps, explain the desirable EL & YM?
• high EL - low YM
what is the composition of CoCr?
• Co (54%) • Cr (25%) • Ni (15%) • Mo (5%) • C (0.4%)
what is a positive reason to use Cobalt in alloys?
• increased strength, hardness, rigidity - coring is possible
in CoCr, what is the function of the chromium?
• increased strength, hardness, rigidity • coring possible • corrosion resistance
how does chromium in CoCr allow for corrosion resistance?
forms a passive layer on the surface of the alloy
what is the purpose of addition of Nickel to CoCr (used in partial dentures)? what is a negative of using this also?
• improves ductility - slight reduction in strength & people may be sensitive/allergic
what are the different casting techniques used for CoCr?
• investment material • melting • casting
how hard is CoCr?
BHN 370
what are some positive reasons to use titanium in partial dentures?
• good biocompatibility • good corrosion resistance • parts can be joined by laser welding
what is a disadvantage of using gold in partial dentures compared to cobalt chromium?
gold is much denser (less comfortable)
what is an advantage of using gold for RPD clasps over cobalt chromium?
gold is less rigid & can therefor flex into undercuts easier