Ceramics
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Give some properties of conventional ceramics
Good aesthetics - colour stable and smooth Chemically stable - inert Biocompatible - inert Thermal properties are good - similar thermal expansion to dentine Dimensionally stable - very stable but 20% shrinkage during firing Good mechanics - high compressive strength, hardness
What are some poor properties of ceramics? What does this mean?
Static fatigue Surface micro-cracks Slow crack growth Ceramics only used in low stress areas
What is sintering?
Fusing of ceramic particles above a threshold temperature
What zirconia is used in dentistry? Why? What des yttria do?
Yttria stabilised zirconia, As pure zirconia can crack on cooling Yttria increased translucency If a crack forms, yttria goes from tetragonal structure back to monoclinic structure (that of normal zirconia) and covers the gap
Some drawbacks of the zirconia production procedure?
CAD/CAM is expensive, cheaper crowns once these bought though Inert fitting surface so no etch or bond
Which crown to use where?
Posterior teeth - monolithic zirconia Anterior teeth single crowns - LiDiSi as very translucent so good aesthetics Anterior bridge - LiDiSi Longer spanning bridges with heavier occlusion - zirconia cored with zirconia where occlusal contacts meet
Difference between decorative and dental ceramic
Decorative ceramic has higher percentage of Kaolin Dental ceramics have more Feldspar and glass particles
What are the optical properties of dental ceramics
Reflectance Translucency Opacity Transparency Opalescence Opacity
How can ceramic be modified to make it more retentive using silane?
Etch with hydrofluorid acid