DeHoff P H, Anusavice K J
Department of Mechanical Engineering and Engineering Science, University of North Carolina, Charlotte 28223.
J Dent Res. 1992 May;71(5):1139-44. doi: 10.1177/00220345920710050201.
Previous studies of opaque-porcelain/body-porcelain discs have shown that compressive stresses which develop in the porcelain surface by being tempered in air can inhibit the sizes of cracks induced within the surface. The objective of this study was to develop a theoretical model for analysis of transient and residual stresses in opaque-porcelain/body-porcelain discs which were produced under variable cooling conditions. The model incorporates the effects of stress and structural relaxation. Transient and residual stresses were calculated for bilayered porcelain discs 16 mm in diameter and 2 mm in thickness for three opaque-porcelain/body-porcelain combinations. Transient temperature distributions in the discs for simulated convective cooling were calculated by finite-element analysis. Data from microhardness indentations reported by Anusavice et al. (1989) indicate that crack lengths measured for bilayered porcelain discs subjected to slow cooling conditions, for which the model predicted residual tensile stresses, were greater than those combinations for which residual compressive stresses were calculated. Calculated values of residual compressive stress for tempered specimens were considerably higher than those for specimens that were slowly cooled and those that were cooled by free convection. In general, residual stress levels calculated by use of the analytical model were in fairly good agreement with the trends observed for crack lengths and bi-axial flexural strengths reported by Anusavice and Hojjatie (1991). The results of the present study indicate that a visco-elastic model is a viable approach for determination of transient and residual stresses in opaque-porcelain/body-porcelain discs.
以往对不透明瓷/体瓷圆盘的研究表明，在空气中回火时瓷表面产生的压应力可抑制表面诱导裂纹的尺寸。本研究的目的是建立一个理论模型，用于分析在可变冷却条件下生产的不透明瓷/体瓷圆盘的瞬态应力和残余应力。该模型考虑了应力和结构松弛的影响。针对三种不透明瓷/体瓷组合，计算了直径16mm、厚度2mm的双层瓷圆盘的瞬态应力和残余应力。通过有限元分析计算了模拟对流冷却时圆盘中的瞬态温度分布。阿努萨维斯等人（1989年）报告的微硬度压痕数据表明，对于模型预测存在残余拉应力的双层瓷圆盘，在缓慢冷却条件下测量的裂纹长度大于计算出存在残余压应力的那些组合。回火试样的残余压应力计算值明显高于缓慢冷却试样和自由对流冷却试样。一般来说，使用分析模型计算的残余应力水平与阿努萨维斯和霍贾蒂（1991年）报告的裂纹长度和双轴弯曲强度的观察趋势相当吻合。本研究结果表明，粘弹性模型是确定不透明瓷/体瓷圆盘瞬态应力和残余应力的一种可行方法。
