Dental ceramics
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What is the composition of dental ceramic
Kaolin <5% Quartz (silica) 12-25% Feldspar 70-80% Metal oxides 1% Glass up to 15%
Why is feldspar added to ceramic
Acts as a flux - prevents oxidation Lowers the fusion and softening temperature of the glass It is the lowest fusing component and flows during firing forming a solid mass around the other components
What are the conponents of porcelain
Feldspar Borax Silica Metallic oxides
What oxides produce what colours
Chromium - GREEN Cobalt - BLUE Copper - GREEN Iron - BROWN Manganese - LAVENDER Nickel - BROWN
What is ceramic powder mixed with to form a restoration
distilled water
What does heating cermaic do
Causes sintering - ceramic particles begin to fuse to a single mass - solid ceramic mass formed
What temp does sintering occur
Just above glass transition temp
How much cotraction occurs with sintering
20%
How are aesthetics favourable
Colour stable Most aesthetic material Smooth surface Retain surface for longer Reflectance Opacity Transparency
Pros of ceramics
Aesthetic Chemically stable Similar thermal properties to teeth Low thermal diffusivity Dimensionally stable
What are the mechanical properties of ceramic
High compressive strength High hardness Low tensile strength Low flextural strength Low fracture toughness Surface micro-cracks Low-crack growth
What are the limitations of ceramic
Low fracture resistance means use is refined to anterior teeth where least stress is applied
How can the low fracture resistance be overcome
Alumina core
What is the sintering temp of zirconia
1600
Why is yttria added to zirconia
increase translucency -decreases physical properties
What ceramic is used for posteriors
Metal ceramic Zirconia core and feldspar porcelain
What are the problems with zirconia cores
Expensive equipment required Potential for veneering porcelain to debond from core Zirconia core is opaque -Are aesthetics much better than metal ceramic? Inert fitting surface, cannot etch or bond
What are the types of milled core crowns and bridges
Zirconia Lithium Disilicate (E-Max) Precious metal Non-precious metal Titanium Composite
What is ceraming
Heated after devsting and cleaning to improve the crystal structure producing crack inhibiting crystals
What ceramic is used for cast and pressed
Lithium disilicate glass Leucite reinforced glass
What are the stages to ceraming
Stage 1 - crystal formation maximum number of crystal nuclei are formed Stage 2 - crystal growth to maximise the physical properties Crystal phase of the ceramic can approach 100%
LiDiSi vs Zirconia crowns
Zirconia stronger LiDiSi more translucent - better aesthetics
What is the strongest crown
Monolithic block crowns
Sintered vs milled
Milled crown is stronger than a buuilt up of pressed crown of the same material