effect of extension and type of composite-restored class ii cavities on biomechanical properties of teeth: a three dimensional finite element analysis.

controversy exists regarding cavity preparation for restoration of interproximal caries in posterior teeth in terms of preserving the tooth structure and suitable stress distribution. this study aimed to assess the effect of extension and type of class ii cavities and the remaining tooth structure in maxillary premolars restored with composite resin on the biomechanical properties of teeth using finite element method (fem).using fem, eight three-dimensional (3d) models of class ii cavities in maxillary premolars with variable mesiodistal (md) dimensions, variable thickness of the residual wall in-between the mesial and distal cavities and different locations of the wall were designed. other dimensions were the same in all models. cavities were restored with composite resin. a load equal to the masticatory force (200n) was applied to the teeth. finite element analysis (fea) was used to calculate the von mises stress.stress in the enamel margin increased by increasing the md dimensions of the cavities. deviation of the residual wall between the mesial and distal cavities from the tooth center was found to be an important factor in increasing stress concentration in the enamel. increasing the md dimensions of the cavity did not cause any increase in stress concentration in dentin.increasing the md dimensions of the cavities, decreasing the thickness of the residual wall between the mesial and distal cavities and its deviation from the tooth center can increase stress concentration in the enamel but not in dentin.