final dental ceramics Flashcards
4 firing temperatures
1) high fusing > 1300C
2) medium fusing =1101 to 1300C
3) low fusing =850 to 1100C
4) ultra low fusing = <850C
what does kaolin do?
hydrated aluminum silicate that acts as a binder to increase the moldability of the unfired porcelain
*small amounts due to opaqueness
denture teeth advantages and disadvantages
- advantages= excellent biocompatibility, natural appearance, high resistance to wear/distortion and dimentionally stable
- disadvantages= brittle, may chip, abrades opposing natural teeth, grinding porcelain is difficult, clicking sound
kaolin is absent in what type of porcelain?
feldspathic porcelain
what is the outstanding feature of metal ceramic porcelain?
resistance to fracture
*low fusing and thermal expansion coefficient is higher than ordinary porcelain
why is it important for expansion and contraction of metal to be slightly greater than porcelain in metal ceramic porcelain?
so that the porcelain remains in constant state of compression
the firing of porcelain is referred to as?
bisque or biscuit bake
what is glaze?
smooth glass formed at surface
importance of glass modifiers in porcelain?
to disrupt integrity of crystalline structure and cross-linking WHICH lowers softening temperature and permits low-fusing porcelain to be produced
adherent oxide verses non-adherent oxide
- adherent= surface oxide of the metal provides transition zone where chemical bond forms
- non adherent= contributes to weak boundary failure
advantages of metal ceramic crown
high strength, used for bridges, excellent fit, less tooth removed when compared to all ceramic crown
disadvantages of metal ceramic crown
appearance of metal margins, discoloration of porcelain (green) by metal, hard to reproduce translucency, bond failure with metals,costly,biocompatibility/thermal
ceramming or partial devitrification
process that causes a portion of amorphous glass to be replaced by crystalline particles
*controlled crystallization
