Dental ceramics
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What is Kaolin?
• Decorative ceramics contain Kaolin • It is a clay • Hydrated Aluminium silicate • Opaque • Opacity imp for appearance of final product
Why does Kaolin need to be removed from Dental ceramics?
• Ceramics need to be translucent so Kaolin removed • Feldspar and silica replace it
What are the components of Decorative ceramic?
• Kaolin 50+% • Quartz (silica) 15-25% • Feldspar 15-25% • Metal oxides <1% • Glass 0
What are the components of Dental ceramics?
• Kaolin <5% • Quartz (silica) 12-25% • Feldspar 70-80% • Metal oxides 1% • Glass up to 15%
What are the two types of Feldspar?
• Potash Feldspar (potassium alumina silicate) • Soda Feldspar (sodium alumina silicate)
What does Feldspar do in dental ceramics?
• Acts as a flux • Lowers fusion and softening temp of glass • Has lowest fusing component and flows during firing forming a solid mass around other components
What are dental ceramics considered as ?
• Glasses
What property do metal oxides gives the ceramic?
• Metallic oxide determine colour of ceramic
What colour does Chromium convey to ceramic?
• Green
What colour does Cobalt convey to ceramic?
• Blue
What colour does Copper convey to ceramic?
• Green
What colour does Iron convey to ceramic?
• Brown
What colour does Manganese convey to ceramic?
• Lavender
What colour does Nickel convey to Ceramic?
• Brown
How are conventional dental ceramics used to build up into a restoration?
• Supplied as a powder • Powder made by heating constituents to high temp >1000oC • Cool rapidly (Fritting) in water • This creates cracks and crazing of ceramic mass • Mill the fritt to fine powder • Add binder (usually starch) • Powder is mixed with distilled water and built up into restoration
What do feldspathic ceramics form when heated to 1150oC-1500oC?
• Form leucites around glass phase of ceramic • Gives powder of known physical and thermal properties • No further chemical reaction needed during fabrication of restoration • Powder melts together to form the crown
What is Leucite?
• Potassium aluminium silicate
How are conventional dental ceramics fabricated?
• Ceramic powder mixed with water and applied to die with brush • Crown built up using different porcelains for dentine and enamel • They are not tooth coloured • Crown is heated in furnace to coalesce the powder into ceramic
What is Sintering?
• Heating the crown leads to Sintering • When the ceramic particles begin to fuse into a single mass • Occurs just above glass transition temp
What happens during sintering of dental ceramic?
• The glass softens and will coalesce • Over time controlled diffusion occurs and solid ceramic mass formed • The material contracts by about 20%
What is meant by the term Coalesce?
• Come together to form one mass or whole
What are some important properties required of conventional dental ceramics?
• Aesthetics • Chemical Stability • Biocompatibility • Thermal Properties • Dimensional Stability • Mechanical Properties
Why do ceramics have the best aesthetics properties of any dental restorative material?
• Colour stable • Very smooth surface • Retain their surface better than other materials leads to less staining long term
What are the optical properties of dental ceramics?
• Reflectance • Translucency • Opacity • Transparency • Opalescence