Metals: Directing the laboratory to do the work Flashcards
(15 cards)
What is the dentists responsibility for materials placed in the mouth
-breakage, discolouration, allerg reaction is attributed to dentist!
so prescribe correct metal for its job.
-specify to lab what material
-understand ur lab and their prefferred material
metals general good properties
high strengh
ductile
withstand loading
good bond between metal and tooth
how are dental alloys cast
lost wax technique
advantages of cad/cam over lost wax
no casting shrinkage
-alloy composition and properties defined
-high internal accuracy
what are intermettalic compunds
2 or more metal
form non mixing layer
clear distinct phases - dull different coloured areas
high mp
what is wrought wire used for
-rpd for deep undercuts (they are cast but dentist bending them makes them worught)
-ortho
What are high noble alloys, charecteristics of them, advantage
alloys w high % of noble metals (gold, palladium, platinum)
adv:
-v malleable,
ductile,
low yield strength (stress before perm deform)
soft enough to burnish
What is burnishability
measure of an alloys yield strength (low) and elongation (high) which gives it the characteristics of being able to adapt to tooth with a burnished
define sag and what dies it lead to
deforming/bending in high temp
leads to casing open margins, poor fit
gold, titanium
what is a metal ceramic retainer
the part of a fixed prosthesis that attaches to the tooth, so the metal part of a PFM
noble vs base metal alloys for metal ceramic retainer?
base metal alloys: high elast modulus, high strenght, diff to control oxide layer,
noble: good but v expensive
requirements for metal ceramic retainer?
-high MP bc of porcelain fusion temp,
high strength,
castable in thin sections,
well defined coeff of thermal expansion bc when heated the metal expands so coeff must match the porcelain one,
controlled oxide formation bc oxidation will make it thicker
concerns with titanium alloys
-hard to process
-expensive equip to process
-many labs not equipped
+stronger than pure titanium
properties of titanium and ti alloys
-elastic mod of 100gpa matches surrounding cortical bone
-high yield strength
-low dentisty
-high mp
mechanical properties of base metals for rpd compared to hardened gold alloy
base metals :
high yield strngth, tensile, but reduced ductility - less susceptible to deformation
High hardness and
greater mod elast to less susceptible to scratches and dents WHICH ARE plaque retentive
