dental ceramics

• kaolin

• it is a clay • hydrated aluminium silicate • opaque

• because they need to be translucent, and kaolin is opaque

• feldspar and silica

• kaolin = 50+% • quartz (silica) = 15-25% • feldspar = 15-25% • metal oxides = <1% • glass = 0

• kaolin = <5% • quartz (silica) = 12-25% • feldspar = 70-80% • metal oxides = 1% • glass = up to 15%

• potassium aluminium silicate

• sodium aluminium silicate

• acts as a reflux • lowers the fusion and softening temperature of the glass • binds the other parts together once you’ve heated them

• chromium = green • cobalt = blue • copper = green • iron = brown • manganese = lavender • nickel = brown

• supplied as powder • powder is made by heating the constituents to a high temperature >1000 degrees • cool rapidly = called fritting • mill the frit to a fine powder • add binder = starch • powder mixed with distilled water and built up into the restorations = something that looks like wet sand • powder then melts together to form the crown

• leucite

• potassium aluminium silicate

• ceramic powder is mixed with water and applied to the die with a brush • crown is built up using different porcelains for dentine and enamel = dentine in pink, enamel purple • not tooth coloured until they have bene fired • crown is heated in a furnace to coalesce the powder into ceramic • heating leads to sintering

• this occurs just above the glass transition temperature • it is when the ceramic particles begin to fuse into a single mass • during sintering the glass phase softens and will coalesce • change from dry powdery mass to a block of ceramic

• about 20% - technician makes it 20% too big to account for this

• best • colour is stable • very smooth surface • retain their surface better than other materials • reflectance • translucency • opacity • transparency • opalescence

• very stable • generally unaffected by the wide pH range found in the mouth • do not take up stain • good biocompatibility

• similar to tooth substance • coefficient of thermal expansion is similar to dentine • thermal diffusivity is low = protects underlying pulp

• once fully fired it is very stable - shrinkage occurs during fabrication which is accounted for by technician

• very strong

• high - can lead to abrasion of the opposing teeth is not glazed

• very low

• very low