Histogenetic aspects of the composition and structure of human ectopic enamel, studied by scanning electron microscopy.

This study was made on 12 enamel projections and 12 enamel pearls on human permanent molars to compare their structure and composition, which might elucidate possible histogenetic differences between these two forms of ectopic enamel. The enamel projections contained approx. 2 (weight)% less Ca and P than control occlusal and mid-coronal enamel. Their mineralization was less homogeneous and probably defective. Their enamel structure was markedly irregular in the prismatic as well as the aprismatic layer, but the composition and structure were very similar to those of the control enamel close to cervical border. The enamel of the pearls largely corresponded in composition and structure to the control occlusal and mid-coronal enamel. The enamel of large pearls also resembled coronal enamel in its compositional and structural variability in the occlusal-cervical direction. These findings suggest that amelogenesis in enamel projections is a continuation of amelogenesis in the cervical region. In contrast, amelogenesis in enamel pearls follows the same pattern as that in a dental crown, from the occlusal region to the cervical enamel border. Therefore, the enamel pearl may well be regarded as an attempt at new tooth formation.