Electron microscopic and microradiographic investigation of a morphologic basis for the mineralization pattern in rat incisor enamel

Abstract

Abstract Although it has been established that human enamel mineralization follows the incremental pattern of matrix secretion, microradiographic studies of rodent enamel still support a non‐incremental pattern of mineralization. This study examines the mineralization sequence using microradiography, as well as measurement of crystal size and distribution on electron micrographs of the various regions of rat incisor enamel. The microradiographic density pattern was found to correlate with the major regions of structural variation within the enamel. Measurement of crystals revealed a rather uniform positive gradation in their size from the surface to the dentino‐enamel junction, i.e., crystal size was found to be directly related to crystal age. Crystal distribution analysis demonstrated that an inner region of enamel contains a much larger volume of crystal‐free space than other areas. This is the same region which has been described as being out of step with an incremental pattern of mineralization, in that it is less dense than enamel either superficial or deep to it. It is concluded that mineral accretion follows the same incremental pattern in the rat incisor as in humans and that the misleading microradiographic image merely reflects a non‐homogeneous distribution of crystals.