Fine Structure of Susceptible Enamel Lamellae against Dentin Caries in the Fissures of Rat Molar Teeth

It has been reported that the fissures of rat molar teeth are apt to cause dental caries. In this study, we observed enamel lamellae in the fissures of caries-free molar teeth of rats, 2 and 4 weeks after birth, by transmitted light microscopy with decalcified sections and by scanning electron microscopy with EDTA-treated samples. Enamel lamellae were always present buccolingually in the fissure enamel. In unerupted teeth, the organic lamellae showing an intermittent structure were composed of the organic matrix, derived from ameloblasts and reduced enamel epithelium, occasionally with these epithelial cells. After eruption, the thin organic membrane of enamel lamellae was probably derived from saliva as well as the organic matrix formed during the enamel formation. The lamellae also contained oral microorganisms and fibrous structures, some of which were formed from microorganisms, under the widely opened fissures containing the deposits of oral microorganisms and diet remnants. Thus, we strongly suggest that such fissure lamellae of rat molar teeth are apt to become the passing point in the way to inducing the dentin caries.