THE EFFECTS OF ENAMEL ANISOTROPY ON THE DISTRIBUTION OF STRESS IN A TOOTH

Enamel is thought to have highly anisotropic stiffness characteristics , because of its prismatic structure. It is probable that the enamel i s stiffer in the prism direction compared with a direction perpendicul ar to it. The prisms are thought to run approximately perpendicular to the enamel-dentin junction. The curvilinear anisotropy that will resu lt can readily be modeled by TOMECH, a finite element program develope d at the University of Sheffield, since curvilinearity of mechanical p roperties is available as an automated feature of this program. The pa tterns of stress due to an external load were investigated in two-dime nsional abstract models, and in a model of a mandibular second premola r, for both anisotropic and isotropic enamel. Results were compared wi th the commercial code ANSYS and good agreement obtained. Enamel with anisotropic properties was found to have a profoundly different stress distribution under load when compared with models with isotropic enam el. For isotropic enamel, the load path is directed through the stiff enamel shell, while for anisotropic enamel, the load path is directed into the dentin, as the load path follows the stiff direction of the e namel prisms. Thus, if enamel is indeed anisotropic, its function diff ers greatly from that suggested in previous hypotheses. Enamel with an isotropic material characteristics would provide a hard-wearing protec tive surface-coating while simultaneously diverting the load away from this brittle, low-tensile-strength phase, thus reducing the potential for tooth fracture.