Abstract
White spots and opaque enamel are characteristics common to dental fluorosis (mottled tooth) and early-stage caries; however, the former shows acid resistance. This study investigated the mechanism of acid resistance in dental fluorosis by comparing the structure and quality of enamel before and after demineralization with 0.1 N HCl, between a mottled tooth and control teeth comprised of an impacted tooth and caries teeth. The teeth were examined macroscopically, by scanning electron microscopy (SEM), and by contact microradiography (CMR). In SEM images of the upper side of demineralized teeth, enamel rods appeared as regularly aligned fish scales in control teeth, while they were observed as irregularly arranged brush-shaped rods in the mottled tooth. The gaps between the rods, formed as a result of demineralization, were wider in the control teeth than in the mottled tooth. In SEM images of the longitudinal sections, the prismless enamel was rough in the control teeth but relatively smooth in the mottled tooth. In CMR of the enamel surface of non-demineralized teeth, a highly calcified layer studded with even more strongly calcified spots was observed in the mottled tooth. These results suggested that acid resistance in the mottled tooth might be attributed to its enamel rod structure, which differed from that of the control teeth. The fluoride level in the drinking water used by the patient with the mottled tooth in this study was 6.1 to 6.7 ppm by absorptiometry and colorimetry, and was high enough to induce dental fluorosis.
