dental ceramics Flashcards
what is the difference between decorative ceramics and dental ceramics
decorative - contain high kaolin and low feldspar
dental -high feldspar and glass - low kaolin
what property does kaolin give to ceramic
opacity
what is the function of feldspar in dental ceramics
lowers fusion and softening temperature of glass
what component of ceramic conveys colour
metallic oxides
how are conventional dental ceramics made
constituents heated to high temperature then cooled rapidly - fritting
frit is milled into a fine power and binder added
powder mixed with distilled water to restore
what is the product when feldspathic ceramics are heated 1150-1500 degrees
leucite (potassium aluminium silicate)
what is the process called when powder is coalesced into ceramic
sintering
3 properties of conventional dental ceramics
aesthetics - optical properties, smooth
biocompatible
chemically stable
normal shrinkage during firing of a conventional feldspathic crown
20%
2 positive mechanical properties of dental ceramics
high compressive strength
high hardness
3 negative mechanical properties of dental ceramic
low flexural strength
low fracture toughness
surface microcracks
where can you use feldspathic conventional ceramics in the mouth and why
only anterior crowns
poor mechanical properties mean can only be used in low stress areas
how can you make a conventional ceramic crown stronger
produce a strong metal coping and cover with the porcelain
alumina core - reinforce with alumina particles
zirconia core - most popular
how do alumina cores strengthen feldspathic porcelain
alumina particles act as crack stoppers and stop cracks propagating through material
opaque so only used in cores
heat required to sinter zirconia
1600 degrees Celsius
what type of zirconia is used in dentistry
yttria stabilised zirconia
what property does yttria have on zirconia
gives translucency - but more yttria reduces physical properties
what structure is zirconia before and after adding yttria
zirconia - monoclinic crystal
yttria - tetragonal crystal
materials used for milled core crowns - 3
zirconia
precious metal - gold
non-precious metal
once divested and cleaned, a cast and pressed ceramic crown is heated to improve its crystal structure - what is this process s called and what are produced in this process
ceraming
produces crack inhibiting crystals
what are the two stages of ceraming
1
crystal formation - max number of crystal npc;ei formed
2
crystal growth to maximise physical properties
what ceramics are used for cast and pressed ceramic processes
glass ceramics e.g. lithium disilicate glass
why is crack propagation difficult in lithium disilicate
needle like crystals
for the same material, what will be stronger a milled or built up or pressed crown
milled
what material might you use for a crown of 36 and why
monolithic zirconia
monolithic block crowns are strongest and woill withstand masticatory forces
zirconia is stronger than LiDiSi
what crown material would you use for a 11 crown and why
LiDiSi
anterior tooth so aesthetics are important factor
LiDiSi has better aesthetics as more translucent
a pt requires an anterior bridge and has parafunction causing heavy occlusion of anterior teeth - what material would you consider
zirconia core with zirconia where occlusal contacts meet
how can you make a silica containing ceramic more retentive
etch with hydrofluoric acid
what do you use to bond ceramic to resin
silane coupling agent
how can you make a zirconia cored crown more retentive
air abrasion
note non silica so unaffected by acid etch
