Effects of systemic fluoride and in vitro fluoride treatment on enamel crystals

Abstract

Systemically administered fluoride at a concentration of 75 ppm increases the surface roughness of developing enamel crystals in rats, which may be significant in advancing our understanding of the biological mechanism of fluorosis. Thus, the aim of this study was to investigate whether the increased surface roughness may be a result of surface restructuring by the direct action of fluoride at the crystal surface. We examined the fluoride dose-dependent roughening of enamel crystal surfaces in vivo, in the rat, and whether this roughening could be mimicked by the in vitro treatment of rat enamel crystals with neutral pH fluoride solutions. Our results showed that enamel crystal surface roughness increased after treatment with increasing fluoride ion concentrations, whether applied in vitro or administered systemically. This suggests a mechanism, alongside others, for the increased surface roughness of crystals in fluorotic enamel.

Figure 1

Tapping mode AFM images of enamel crystals on a mica surface, imaged in air. (a) Control (maturation stage); (b) maturation-stage enamel crystals from rats after systemic administration of 50 ppm fluoride for 21 days; (c) maturation-stage non-fluorotic enamel crystals after in vitro treatment with 50 ppm fluoride, pH 7.4, for 21 days at 37°C; (d) maturation-stage non-fluorotic enamel crystals after in vitro treatment with 1000 ppm fluoride, pH 7.4, for 18 hrs at 37°C. [a-d image sizes, 1 × 1 μm; bar = 100 nm; left, height image, z-range, 100 nm; right, phase image, z-range, 60°.]

Figure 2

Surface roughness measurements (R_a ± SD) of maturation-stage enamel crystals after in vivo or in vitro treatment of fluoride. In vivo treatment (rats received systemically different concentrations of fluoride in their drinking water, added as NaF, for 21 days): A (control), B (25 ppm), C (50 ppm), D (75 ppm). [B and C are not significantly different from each other (P < 0.05).] Maturation-stage enamel crystals treated in vitro with NaF at different concentrations for 21 days at 37°C: E (control), F (25 ppm), G (50 ppm), H (75 ppm) [not significantly different from each other (P < 0.05)]. Maturation-stage enamel crystals treated in vitro with NaF in different concentrations for 18 hrs at 37°C: I (control), J (200 ppm), K (1000 ppm), L (2000 ppm), M (10,000 ppm), N (20,000 ppm) [J, K, L, M, N are significantly different from the control, I; J and K are not significantly different from each other but are significantly different from L, M, N; L, M, N are significantly different from each other (P < 0.05)].