Dental Ceramics
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what is kaolin
clay
why is kaolin removed from dental ceramics
it is opaque but dental ceramics need to be translucent
what replaces kaolin
feldspar and silica
what is the process of conventional dental ceramics
powder is heated then rapidly cooled milled to fine powder binder added mixed with distilled water and built up into restoration
what do feldspathic ceramics form when heated
leucite
what does leucite give the powder
physical and thermal properties
how is a crown fabricated
ceramic powder mixed with water and applied to die with brush crown built up using different porcelains for dentine and enamel crown heated in furnace
what is sintering
ceramic particles begin to fuse into a single mass
what happens to the material during sintering
contracts
what are the properties of conventional dental ceramics
aesthetics - good chemical stability - good biocompatibility - good thermal properties - similar to tooth dimensional stability - good mechanical properties
what are the mechanical properties of dental ceramics
high compressive strength high hardness low tensile strength low flexural strength low fracture toughness
what is static fatigue
time dependent decrease in strength even in absence of any applied load
where can conventional feldspathic ceramic crowns be used
low stress areas anterior crowns
how do you overcome problems with conventional ceramics
produce a strong coping
what are the 2 types of core used in a crown
alumina or zirconia
what does alumina act as
crack stoppers preventing cracks propagating through material and causing fracture
what are the problems of alumina cores
lack of flexural strength only successful anteriorly
what zirconia is used in dentistry
Yttria stabilised
what does yttria make the material
hard strong tough
how is a zirconia core made
impression taken and model cast digitally scanned software creates bridge milling heat treated and stained veneered with feldspathic porcelain
what are the problem with zirconia cored crowns
expensive equipment needed could debond from core cannot etch or bond
what is used for posterior teeth
monolithic zirconia
what is used for anterior teeth
lithium disilicate
what is used for anterior bridgework
lithium disilicate