Stress Distribution in Teeth Due to Dimensional Changes of the Restorative Material

Abstract

The objective of this paper is to theoretically investigate the stress distribution in a tooth model due to expansion or contraction of the filler material. Finite element calculations were carried out to determine the stresses and deformations in a model of the tooth. The tooth was modelled to consist of two concentric cylinders, an inner cylinder of 7 mm diameter dentine and an outer layer of 1 mm thick enamel. The two cylinders were assumed to be rigidly fixed at the bottom end and the top end was free. Different sizes of occlusal cavities (2, 4 and 7 mm) as well as mesial-occlusal and mesial-occlusal-distal were simulated through removal of dentine from the centre. The fillings were subjected to an internal pressure of 1 MPa and a chewing pressure of 1 MPa. Since the cylinders were rigidly fixed at one end, the inner part of the cavity (dentine) tended to bend outwards, thus compressing the outer (enamel) layer. This behaviour, coupled with a strong mismatch of the elastic moduli of dentine and enamel, leads to widely different distributions of stress in the tooth as the cavity sizes and filling types are varied. The radial deformations were of the order of microns, most of it occurring in the softer dentine. The maximum stresses occur in the stiffer enamel layer when a chewing pressure is applied, without a chewing pressure the stresses are more evenly distributed.