The pathway of enamel rods at the base of cusps of human teeth.

Enamel increases in volume and surface area with distance from the dentin-enamel junction, particularly at cusps, while the number of rods remains constant. Our results indicate that the increase in volume may be due to the increased rod diameter near the tooth surface, a circumferential winding of rods in the parazone orientation of Hunter-Schreger bands, and the migration of rods from a mid-coronal origin at the dentin surface to a cuspal terminaton at the tooth surface. Increased surface area can be explained by the increased rod diameter and the oblique approach of rods to the tooth surface.