A finite element analysis (FEA) of a mandibular molar restored with Class II amalgam restoration was conducted to determine the stress distribution which results from a superposition of simultaneous mechanical and thermal loading. A fully crossed three-level four-factor experimental design was used to evaluate the relative influence of crown temperature, time of thermal loading, occlusal force, and cavo-surface margin adhesion on the stress distribution. It was found that occlusal force and temperature had significant influence on the stress distribution and particularly on the maximum principal stress. Over the range in oral conditions considered, thermal loading contributed for over 35% of the stress within the restored molar subjected to simultaneous mechanical and thermal loads. Furthermore, thermal loading had significant effects on the magnitude of normal stress that develops parallel to the pulpal floor. Although marginal bonding of amalgam reduces the stress resulting from occlusal forces, thermal loading promotes the development of significant interfacial shear stresses along the bonded margin. Stresses related to the thermal component of loading concentrate near the pulpal floor and lingual surface margin, the site most prominent in cusp fracture. Hence, results from this study clearly indicate that an evaluation of new dental materials and/or restorative designs should consider the effects from a superposition of simultaneous mechanical and thermal loads on fracture resistance.
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