Waxes Flashcards
describe the lost wax technique
- pt is assessed
- imporession is taken
- master model is created
- wax up is created
- is put into carbon crucible AND INVESTED; IF USING GOLD, WILL USE GYPSUM-BONDED INVESMEN; if using CoCr alloys, phosphate-bonded investment is used
- gold is put into crucible and put in centrifuge–>casting
- new metal model is divested
- crown is prepared
- is veneered
- implanted/attached to crown
what are the desirable properties of waxes?
-easily formed into desirable shape
- carves cleanly (no smearing)
- good dim. stab – low shrinkage and stable during storage
- adequate storage
non toxic, allergenic
what are the types of wax
pattern and inlay wax
- use for direct (softening range = 38-45 degrees c)
-type II use for indirect
softening range = 30-45 C
can also classify waxes based of chemical make up –>hydrocarbonvs esters
ye
can classify waxes based on origin –>
mineral = paraffin anumal = spermacet plant = carnuba insect = beeswax synthetic = acrawax
ye
what is inlay waxes used for?
make patterns for inlays, onlays, and crowns
what are some important properties for inlay waxes?
- must adapt well to dies
- rigid for carving but does not flake or chip
- good thermal stability –> at low temps and when it is being heated for use
- capable of complete and clean pyrolysis (e.g. burns away out of set investment)
- must stay hard at mouth temp
what is the compositionof inlay wax?
- paraffin (60%) = base wax
- carnuba = (25%) modifier wax
- ceresin (10%) = modifer wax
- beeswax (5%) = stickiness to die (also a modifer wax)
- colourant (<1%)
the carnuba and ceresin INCREASE HARDNESS, whereas the beeswax and colourant increase STICKINESS
excessive heating about the liquidus line causes decomposition
ye
what are the requirements on casting investments
- expansion 1.2-2.2% compensation for alloy shrinkage – gold alloy shrinks 1.4-1.7%, and base metal contract 2.0-2.3
- accuracy (resistance to distortion during setting time)
- strength: resistance to casting forces and high temps
