前牙全瓷冠饰瓷崩裂断口形貌分析

Fractographic analysis of clinically failed anterior all ceramic crowns

目的通过断口形貌观察分析临床失效的前牙全瓷冠，分析疲劳损伤的起源和发展，以期为优化全瓷冠桥修复体的临床设计及修复工艺提供依据。方法收集临床失效前牙二硅酸锂基瓷冠（IPSEmpress11）3例，玻璃渗透氧化铝瓷冠（In—Ceram）2例，采用体视显微镜和扫描电子显微镜观察断裂面，分析特征形貌。结果5例全瓷冠主要失效模式均为唇侧饰瓷内聚破坏，裂纹起源于切端咬合接触区，并由切端向龈端扩展，裂纹源附近饰瓷内部见较多气孔缺陷。结论饰瓷内聚破坏是全瓷修复失效的重要原因；饰瓷内部易出现制作缺陷，成为双层瓷修复体的薄弱环节；改良饰瓷制作及烧结工艺，设计多点咬合接触将有助于减少饰瓷崩瓷。

Objective To identify the site of crack initiation and propagation path of clinically failed all ceramic crowns by fractographic analysis. Methods Three clinically failed anterior IPS Empress Ⅱ crowns and two anterior In-Ceram alumina crowns were retrieved. Fracture surfaces were examined using both optical stereo and scanning electron microscopy. Fractographic theory and fracture mechanics principles were applied to disclose the damage characteristics and fracture mode. Results All the crowns failed by cohesive failure within the veneer on the labial surface. Critical crack originated at the incisal contact area and propagated gingivally. Porosity was found within the veneer because of slurry preparation and the sintering of veneer powder. Conclusions Cohesive failure within the veneer is the main failure mode of all ceramic crown. Veneer becomes vulnerable when flaws are present. To reduce the chances of chipping, multi-point occlusal contacts are recommended, and layering and sintering technique of veneering layer should also be improved.