STUDY ON LIFETIME PREDICTION FOR DENTAL CERAMICS

本文从揭示材料寿命后再使用牙陶瓷的观点出发，对影响牙陶瓷寿命和疲劳失效的因素进行了研究。(1)采用Chervon缺口法测定了不同成分的金属陶瓷和烧结磷灰石的临界应力强度因子K_<IC>。与氧化铝相比，这些陶瓷的K_<IC>值较低。利用K_<IC>和矩形平行六面体共振法测量的弹性常数计算了它们的断裂能。其中烧结磷灰石的值很小，不宜用于口腔。(2)根据预裂纹长度和预裂纹再次扩展时的声发射监测得到的应力，估算了湿态条件下金属陶瓷在腐蚀极限K_<IO>处的应力强度因子。该值为K_<IC>的64%，表明裂纹在口应力条件下发生应力腐蚀扩展。(3)采用v形缺口试样测量了不同溶液中表观K_<IC>，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)通过重复十字头的停移，对金属陶瓷的v形缺口瓷试样进行了稳定裂纹扩展测量。研究发现，白晶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.