STUDY ON LIFETIME PREDICTION FOR DENTAL CERAMICS

本研究旨在阐明影响牙科陶瓷材料寿命和疲劳破坏的因素，并提出在揭示材料寿命后再利用牙科陶瓷材料的观点。(1)本文用切尔冯缺口法测定了<IC>不同成分的金属陶瓷和烧结磷灰石的瓷的临界应力强度因子K。与<IC>氧化铝相比，这些陶瓷的K值较低。用<IC>矩形平行四边形共振法测得的K_2和弹性常数计算了它们的断裂能。尤其是烧结型磷灰石，其值很小，不宜用于口腔。(2)根据<IO>预裂纹长度和预裂纹重新开始生长时的声发射测量应力，估算了金属陶瓷瓷在潮湿条件下的腐蚀极限应力强度因子K_。该值为K_（1/2）的64%<IC>，表明应力腐蚀裂纹扩展发生在口腔应力条件下。(3)本文用V形缺口试样在不同溶液中的表观K值，研究了腐蚀性材料对金属陶瓷瓷裂纹扩展的影响<IC>。结果表明，水是应力腐蚀促进裂纹扩展的主要因素。(4)采用人字形缺口陶瓷试件，通过十字头的反复停移，实现了金属陶瓷裂纹扩展的稳定测量。结果表明，白榴石晶体在很大程度上有助于防止裂纹扩展。

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.