DM - ceramics Flashcards
what is incorporated in dental porcelain that makes it more opaque and stronger?
leucite
how is dental porcelain customised to match dental alloys?
expansion/ contraction customised to match range of dental alloys - aims to have slightly higher expansion/ contraction that the underlying alloy to put porcelain in slight tangential compression
what are the 2 ingredients that make porcelain?
kaolin
feldspar
what does koalin do to porcelain?
gives tooth plasticity and allows formation of tooth structure
what does fledspar do to porcelain?
hardness and translucent appearance
what is added to porcelain to promote scattering of light and colouration (opalescence)?
particles of metal oxides
what does compaction do to poreclain when mixing?
brings particles together
patting/ vibration
blotting removes moisture
reduces firing shrinkage
what does firing do when mixing poreclain?
reduces porosity
controlled cooling to avoid cracking
how do you limit crack propagation in poreclain?
have an aluminium core (pure)
add alumina powder
sintered aluminium core
metal core - PFM
what are PFM alloys?
poreclain fused metal
what are the desirable properties of PFM alloys?
not melt when firing
rigid to support thin veneer
bond to poreclain
similar coefficient of thermal expansion to poreclain
what are the types of available PFM alloys?
high gold
low gold
silver palladium
nickel chromium
what technique is used to overcome shrinkage?
lost wax technique
why are filler particles added to feldspathic glasses?
improve mechanical properties
improve opalescence, colour and opacity
what filler are added to feldspathic glasses?
leucite (strengthening)
particles of AlO (etches at greater rate)
how are filler particles added to feldspathic glasses?
mixed in factory
grown in pressed pellet for heat treatments
list properties of polycrystalline ceramics
no glassy components
atoms packed in dense arrays (inhibits crack)
relatively opaque
how many layers are in polycrystalline ceramics?
6
what are the 3 allotropes of zirconia?
cubic
tetragonal
monoclinic
what are allotropic forms of carbon?
diamond and graphite
list properties of ceramic
aesthetic
prone to crack propagation
brittle
list properties of porcelain
hard
resistant to chemical attack
good thermal isulator
how may you modify porcelain to prevent, to an extent, degree of crack propagation?
add glaze surface
how can you maximise clinical durability of ceramics?
use max occlusal thickness
use highest elastic modulus substrate possible for core
bond the restoration
develop broad occlusal contacts
