Importance of Considering the Gradient of Tooth Properties in FEM
Objectives: The aim of this study is to ascertain whether the consideration of the Young’s modulus gradient (in the dentin-enamel junction (DEJ), enamel and dentin) has a substantial impact on the stress distribution experienced by the tooth. The experimental data demonstrate that these tissues exhibit significant property gradients. Methods: Four models of simplified molar were created in a finite element model (Forge NxT 4.0, TRANSVALOR, France): one with no gradient (i.e., the Young’s modulus is constant in each tissue, Edentin = 18.6GPa, Eenamel = 84GPa), another one with a gradient for DEJ (transition between the Young’s moduli of enamel and dentin over a thickness of 100μm), one with the same gradient for DEJ and another one for enamel (70GPa < Eenamel < 100GPa) and a gradient for DEJ, enamel and dentin (15GPa < Edentin < 20GPa). A sensitivity analysis of the mesh element size was conducted. Results: The gradient for DEJ has no significant impact on the results. The gradient in the enamel changes how the stress is distributed in the enamel. The stress levels are significantly higher on the proximal faces (~13MPa to ~15MPa) and in the tooth groove (~30MPa to ~35MPa), but lower and less extended near the DEJ (~26MPa to ~22MPa). The gradient in the dentine causes the zone of maximum stress to spread over the proximal surfaces. Conclusions: Failing to account for the enamel gradient during the simulation process can result in an inaccurate stress distribution. This result supports the idea that using a restorative material with homogeneous mechanical properties to fill a tooth cavity is likely to result in failures at the proximal surfaces or in the tooth groove.