STUDY ON LIFETIME PREDICTION FOR DENTAL CERAMICS

为了阐明牙科陶瓷材料寿命的影响因素和疲劳破坏的原因，提出了牙科陶瓷材料应在揭示材料寿命后才能使用的观点。(1)用Chervon缺口法测量了金属陶瓷和不同成分的烧结磷灰石陶瓷的临界应力强度因子K&lt；Ic&gt；与氧化铝相比，这些陶瓷的K&lt；IC&gt；值较低。用K&lt；IC&gt；和矩形六面体共振法测得的弹性常数计算了它们的断裂能。(2)根据预裂纹长和通过监测预裂纹声发射确定的应力，估算了金属陶瓷瓷在湿条件下的腐蚀极限应力强度因子K_&lt；IO&gt；该值为K&lt；IC&gt；的%，表明应力腐蚀裂纹扩展是在口腔应力条件下发生的。(3)采用人字形缺口试件测量不同溶液中金属陶瓷的表观K&lt；IC&gt；，研究了腐蚀材料对金属陶瓷裂纹扩展的影响。结果表明，水是促进应力腐蚀裂纹扩展的主要因素。(4)利用金属陶瓷人字形缺口试件，通过重复十字头的停动，进行了裂纹的稳定扩展测量。结果表明，白榴石晶体在很大程度上阻止了裂纹的扩展。

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.