A 3-DIMENSIONAL FINITE-ELEMENT MODEL OF PRISMATIC ENAMEL - A REAPPRAISAL OF THE DATA ON THE YOUNG MODULUS OF ENAMEL

The inconsistencies of published data on the Young's modulus of dental enamel, the parameter used to quantify stiffness, have, for a long ti me, restricted our understanding of the biomechanical behavior of teet h. With the use of modeling techniques, the aim of this paper is to in vestigate which of the data may be more reliable. Ln this way, the pos sible causes of the discrepancies in data will be addressed. Two diffe rent structural levels are considered within the model. At an ultrastr uctural (i.e., crystalline) level, the model considers enamel to behav e as a simple composite, being made up of long, parallel crystals held together by an organic matrix. At this level, the stiffness of enamel is predicted by simple composite theory, and the model indicates that stiffness is dependent on chemical composition and crystal orientatio n. At a microstructural (i.e., prismatic) level, the model considers e namel to behave as a hierarchical composite, being made up of prisms, in which the crystal orientation is heterogeneous. At this level, the stiffness of enamel is predicted by finite element stress analysis, an d values of predicted stiffness are found to be dependent on both chem ical composition and prism orientation. Within a realistic composition al range, predicted values of Young's modulus along the direction of p risms are comparable with the corresponding experimental values of 77. 9 +/- 4.8 GPa obtained by Craig et al. (1961) and 73 GPa obtained by G ilmore et al. (1970), but not with those low values of 9.65 +/- 3.45 o btained by Stanford et al. (1960). Predictions of Young's modulus valu es across the direction of prisms are also made, and the model is less stiff in this direction. These findings indicate that human prismatic enamel is almost certainly anisotropic with respect to stiffness.