The enamel of human teeth is composed of parallel rods (bundles) of long, closely-packed, ribbonlike hydroxyapatite (HAP) Ca10(PO4)6(OH)2 crystallites oriented normal to the tooth surface. Both the unique structure of the crystallites and the higher order arrangement of the crystallites are believed to be a consequence of interactions between proteins secreted by the enamel forming tissues and the growing crystallites. A better understanding of the precise molecular mechanism that controls enamel crystallite formation could potentially lead to both novel enamel repair strategies and crystal growth control systems. It has been previously reported that the unidirectional flow of calcium ions across a membrane can be used to form ribbon-like structures of a related form of calcium phosphate. We have created a similar model system which utilizes the unidirectional flow of calcium ions to generate ribbon-like HAP crystallites. Ultimately, this system will be modified so that enamel proteins can be introduced into the crystallization milieu to better characterize their role in enamel formation.

SEM and TEM samples were prepared using the experimental setup shown in Fig. 1. Several tubes containing a 50mM HAP solution dissolved in 0.1M HC1 were placed upside down into a 50mM MOPS pH buffering solution at pH 7.0.