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.