Three-dimensional biomechanical study of functional stresses in composite restorations of masticatory teeth

The aim of the present work was to study and evaluate the intensity of stresses in the adhesive bond in composite restorations of masticatory teeth after light-curing, under temperature changes and masticatory loads.

Data for the 3D model generation of a maxillary premolar were obtained during a routine CT head scan. Thirty-three cross-sections of tooth 25 were selected and used to create a 3D geometric model enmeshed using the finite element method (FEM) (made up of 106556 elements and 608724 nodes). The pulp cavity and the periodontal ligament were constructed in the same way and integrated into the premolar model. Eight cavity configurations with converging walls were designed, resistant to masticatory forces (enamel/dentin = 1/1). A comparative computer simulation was carried out of the polymerization shrinkage forces of the composite material (CM), temperature changes in the oral cavity and functional masticatory loads. The distribution of the generated stress on the adhesive bond was evaluated in eight different class I and II cavity configurations. The location of crack formation was assessed in the cases of rupture of the adhesive bond.

In all cavity configurations, stress concentration in the adhesive layer is higher at the interface with the dental tissues. Low temperatures (5 degrees C) generate forces that are greater than the strength of the adhesive bond in all studied cavity configurations. The distribution of the generated stresses under the effect of axial and tangent forces of 300 N is similar to that under the effect of temperature factors. The axial masticatory forces have a pronounced adverse effect on the adhesive bond in all cavity configurations.

Low temperatures and axial masticatory forces play an important role for the marginal integrity. They exacerbate the adverse effects of polymerization shrinkage in composite restorations of masticatory teeth.