Dental Ceramics Flashcards
is all ceramic porcelain
all porcelain is ceramic but not all ceramic is porcelain
what is the difference between dental ceramics and decorative ceramics
decorative contain kaolin which is an opaque material, dental materials should be translucent so have kaolin removed
what is kaolin replaced with in dental porcelains
feldspar and silica
what are dental ceramics made up of
feldspar, borax, silica and metallic oxides
(metallic oxides convey their colour to the ceramic e.g copper gives green tinge)
sintering
process in which particles fuse to form a solid mass
how much shrinkage is experienced by conventional dental ceramics during sintering
20% - requires a highly skilled technician to accomodate for this
discuss the properties of conventional dental ceramics
excellent aesthetics
good thermal properties (similar to tooth)
chemically and dimensionally stable
low fracture toughness
low flexural strength
prone to microcracks
shrinkage during fabrication requires skilled technician
where might conventional feldspathic dental ceramics be used
only in low stress areas sue to poor strength properties
e.g anteriors in suitable patient
what makes porcelains have such good aesthetics
colour stable
very smooth surface
less prone to staining
good optical properties - reflectance, translucency, opacity, transparency etc
discuss the pros and cons of alumina porcelain as a dental material
pros: alumina particles act as crack stoppers preventing cracks propagating and causing fracture
cons: alumina porcelain is opaque so requires feldspathic layer above so more tooth reduction may be required also inadequate flexural strength. Can only be used anteriorly
what is added to dental zirconia and what effect does this have on the material
dental zirconia is yttria stabilised (3-5%)
more yttria means more translucency however reduced physical properties
why is the structure of dental zirconia compared with normal zirconia significant
normal zirconia is a monoclinic crystal structure at room temperature
yttria has a tetragonal crystal structure
in dental zirconia , if crack begins to form, pressure reaches a level that turns the tetragonal structure to monoclinic. This involves a slight expansion which closes up the crack
discuss the pros and cons of dental zirconia
pros: crack/ fracture resistant, hard, strong, tough, excellent fit
cons: expensive equipment - CAD-CAM required, core is opaque so requires veneering with feldspathic porcelain, veneering porcelain may debond from core.
what piece of equipment is required to fabricate a milled crown
CAD-CAM
what are the strongest type of crowns
monolithic block crowns
(crowns milled from a single block of material)
