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首页> 外文期刊>The Journal of Prosthetic Dentistry >Effect of luting composite shrinkage and thermal loads on the stress distribution in porcelain laminate veneers.
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Effect of luting composite shrinkage and thermal loads on the stress distribution in porcelain laminate veneers.

机译：复合材料的收缩率和热负荷对瓷层压板表面应力分布的影响。

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STATEMENT OF PROBLEM: Cyclic thermal fatigue has demonstrated a significant influence of the thicknesses of luting composite and ceramic in crack propensity of porcelain laminates. PURPOSE: This study was conducted to define potentially involved parameters for crack development in porcelain laminates bonded to teeth. Finite element modeling was used to evaluate the respective effects of luting composite shrinkage and significant thermal changes. MATERIAL AND METHODS: A buccolingual cross-section of a maxillary incisor was digitized and used as a template to generate a single 2-dimensional mesh, including all the different restorative designs. Luting composite shrinkage was simulated at a baseline temperature of 20 degrees C. The effect of thermal loads from 20 degrees C to 5 degrees C and from 20 degrees C to 50 degrees C was assessed with and without preexisting composite shrinkage. RESULTS: Shrinkage of the luting composite alone generated important compressive forces on the ceramic, either at the restoration surface or interface. Compression intensity was related to geometry and ratio of thicknesses between the ceramic and luting composite (CER/CPR). Lower ratios produced higher compression forces in the ceramic. When thermal loads were combined to the composite shrinking forces, the stress pattern was significantly changed only for the experimental conditions with the lowest CER/CPR ratio. Temperature increase reduced compressive stresses and exacerbated tensile stresses. Thermal loads were simulated alone (situation of an "ideal nonshrinking" luting composite) and generated mainly tensile stresses in the ceramic, which intensity was again modulated by the CER/CPR ratio and the local geometry of composite and ceramic. Because of ceramic brittleness, these tensile forces were more detrimental than the high compression created by composite shrinkage alone. The stress pattern was not influenced by the incisal length of the veneer but rather by the facial thickness of ceramic. The worst record made with a shrinking luting agent (500 microm of luting composite, lowest CER/CPR ratio, 5 degrees C) was much less harmful than the worst record made with a hypothetical "nonshrinking" luting material. CONCLUSIONS: The ratio of the thickness of cement and luting composite appears to have a relevant influence on the stress distribution in porcelain laminates. Restorations that are too thin, combined with poor internal fit, resulted in higher stresses at both the surface and interface of the restoration. Because of its precompressed state given by composite shrinkage, ceramics performed better with regard to temperature-induced tensile forces.
机译：问题陈述：循环热疲劳表明，胶合复合材料和陶瓷的厚度对瓷层压板的裂纹倾向具有重大影响。目的：进行这项研究的目的是确定粘结在牙齿上的陶瓷层压板中可能产生的裂纹扩展参数。有限元建模被用来评估复合材料收缩和明显的热变化的相应影响。材料和方法：将上颌切牙的颊舌横截面数字化，并用作生成单个二维网格的模板，包括所有不同的修复设计。在基准温度为20摄氏度时模拟了Luting复合材料的收缩。在有和没有预先存在复合材料收缩的情况下，评估了20摄氏度至5摄氏度以及20摄氏度至50摄氏度的热负荷影响。结果：单独的浸润复合材料收缩会在修复表面或界面处对陶瓷产生重要的压缩力。压缩强度与陶瓷和浸润复合材料之间的几何形状和厚度比（CER / CPR）有关。较低的比率在陶瓷中产生较高的压缩力。当热负荷与复合材料的收缩力结合在一起时，应力模式仅在具有最低CER / CPR比的实验条件下才发生显着变化。温度升高降低了压缩应力并加剧了拉伸应力。单独模拟热负荷（“理想的非收缩”浸润复合材料的情况），并在陶瓷中主要产生拉伸应力，该强度再次受到CER / CPR比以及复合材料和陶瓷的局部几何形状的调节。由于陶瓷的脆性，这些拉伸力比仅由复合材料收缩产生的高压缩力更有害。应力模式不受单板切面长度的影响，而受陶瓷表面厚度的影响。用收缩的浸润剂（500微米的浸润复合材料，最低的CER / CPR比，5摄氏度）制成的最差记录的危害性远小于使用假定的“不收缩”浸润材料制成的最差记录。结论：水泥与胶合料的厚度比似乎对瓷层压板中的应力分布有重要影响。修复体太薄，再加上内部适配性差，导致修复体的表面和界面处的应力更高。由于复合收缩带来的预压缩状态，陶瓷在温度引起的拉力方面表现更好。

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