RESUMO
<p><b>OBJECTIVE</b>To investigate the ultrastructure of enamel in the mandibular incisor tooth in a rat model of dental fluorosis.</p><p><b>METHODS</b>Thirty 5-week-old male and female rats of SD strain were divided into three groups of ten. The animals in the control group were maintained for 8 weeks on pure deionized water, in the low-fluoride group deionized water with 22.5 mg/L of fluorine (50 mg/L NaF) was used, and in the high-fluoride group deionized water with 45 mg/L of fluorine (100 mg/L NaF) was used. All specimens examined were obtained from the mandibular incisors. Mid-sagittal ground sections were prepared from the direction of incisal point of each incisor for scanning electron microscopy (SEM) and atomic force microscopy (AFM).</p><p><b>RESULTS</b>According to the SEM results, the prisms in the control group had a complete and clear column structure with closely packed enamel rods or enamel prisms. The prisms in the high-fluoride experimental group were collapsed and showed curved and fractured crystallites. The level of prism structural changes in the low-fluoride experimental group was in between that of the control group and the high-fluoride group. AFM for the middle layer enamel showed an average roughness (Ra) of (550.6±32.0) nm in the control group, (415.0±24.2) nm in the low-fluoride group, and (194.3±11.3) nm for the high-fluoride group. There was significant difference between the high-fluoride group and the control group (P<0.05).</p><p><b>CONCLUSIONS</b>Formation of rat enamel in the high fluoride environment presented obvious structural collapse and no clearance between prisms. Such changes appear to indicate a loss of normal prism structure in rat enamels from exposure to high levels of fluorine during the maturation period.</p>