The influence of simultaneous mechanical and thermal loads on the stress distribution in molars with amalgam restorations

A finite element analysis (FEA) of a mandibular molar restored with Class I I amalgam restoration was conducted to determine the stress distribution wh ich results from a superposition of simultaneous mechanical and thermal loa ding. A fully crossed three-level four-factor experimental design was used to evaluate the relative influence of crown temperature, time of thermal lo ading, occlusal force, and cavo-surface margin adhesion on the stress distr ibution. It was found that occlusal force and temperature had significant i nfluence on the stress distribution and particularly on the maximum princip al stress. Over the range in oral conditions considered, thermal loading co ntributed for over 35% of the stress within the restored molar subjected to simultaneous mechanical and thermal loads. Furthermore, thermal loading ha d significant effects on the magnitude of normal stress that develops paral lel to the pulpal floor. Although marginal bonding of amalgam reduces the s tress resulting from occlusal forces, thermal loading promotes the developm ent of significant interfacial shear stresses along the bonded margin. Stre sses related to the thermal component of loading concentrate near the pulpa l floor and lingual surface margin, the site most prominent in cusp fractur e. Hence, results from this study clearly indicate that an evaluation of ne w dental materials and/or restorative designs should consider the effects f rom a superposition of simultaneous mechanical and thermal loads on fractur e resistance (C) 2000 Kluwer Academic Publishers.