Distribution of Enamel Crystallite Orientation through an Entire Tooth Crown studied using Synchrotron X-Ray Diffraction

The biomineralization of human dental enamel has resulted in a highly anisotropic and
heterogeneous distribution of hydroxyapatite crystallites, which in combination with
its high mineral content has resulted in one of the most durable and hardest tissues in
the human body. In this study, we used position-sensitive synchrotron X-ray diffrac-
tion to quantify the spatial variation in the direction and magnitude of the preferred
orientation of enamel crystallites across a whole tooth crown. Two-dimensional syn-
chrotron X-ray diffraction images were collected with 300 lm spatial resolution over a
series of six sequential tooth sections obtained from a single maxillary first premolar
and were analyzed using Rietveld refinement. Both the magnitude and the direction of
the crystallite orientation were found to have a high spatial heterogeneity. Areas of
high crystallite alignment were directed perpendicular to the biting surfaces, which is
thought to meet the functional requirements of mastication. The results may assist in
our understanding of the structure–function relationship and of the evolutionary
development of enamel.