STUDY ON LIFETIME PREDICTION FOR DENTAL CERAMICS

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This study has been made to clarify the factors affecting a lifetime and a fatigue failure on dental ceramics on the basis of idea that the dental ceramics should be utilized after revealing the lifetime of materials.(1) Chervon notch method was applied to measure the critical stress intensity factor K_<IC> of porcelain for metal ceramics and sintered apatites with various compositions. K_<IC> of these ceramics showed lower values compared with alumina. The fracture energies of them were calculated using both K_<IC> and elastic constants measured by rectangular parallelepiped resonance method. The values of them were not enough for use, especially, that of sintered apatite was quiet small and was considered not to use in oral.(2) The stress intensity factor at corrosion limit K_<IO> of porcelain for metal ceramics was estimated in wet condition from the precrack length and the stress determined by monitering the acoustic emission when the precrack started again to grow. The value was 64% of K_<IC> and suggested that the crack growth by stress corrosion would take place in oral stress condition.(3) The effect of corrosive materials affecting the crack extension of porcelain for metal ceramics was investigated by measuring the apparent K_<IC> in various solutions using chevron notched specimens. The result suggested that the water was the main factor for promoting the crack extension by stress corrosion.(4) The stable crack extension measurement using chevron notched porcelain specimen for metal ceramics was made by repeating the stop-and-move of crosshead. It was found that the leucite crystals largely contributed to prevent the crack growth.