Ultrastructure and Composition of Enamel in Human Dental Fluorosis

Abstract

Materials used in this work were 13 permanent molars exhibiting dental fluorosis (between 5 and 9 on the Thylstrup-Fejerskov scale, 1978) obtained from adults (aged 20-40 years) living in regions with 3.5 ppm fluoride in the water supplies. Small but deep occlusal caries lesions necessitated extraction. Light and polarized microscopic, microradiographic, electron microscopic, and electron-probe- and ion-micro-analytical studies were made. Enamel surfaces were generally cloudy to opaque, with several pits or defects of various sizes and degrees of brown-staining. An extensively hypomineralized area extended from the inner enamel to the surface layer, which was mineralized to a high degree. The hypomineralized area contained sparsely arranged, flattened, hexagonal crystals with either perforated centers or defects extending from the perimeter and indicating either no or low fluoride content. The highly mineralized surface layer, however, was composed of many large, flattened, hexagonal crystals and extremely small, irregularly shaped crystals. Both types were free of central perforations and defects. A high fluoride concentration was determined in the highly mineralized surface layer. These findings suggest that the hypomineralized area undergoes caries-like changes in terms of crystal dissolution and that the highly mineralized surface layer contains hydroxyapatite and fluoridated-hydroxyapatite, or fluorapatite, or both.

The Impact of Fluoride on Ameloblasts and the Mechanisms of Enamel Fluorosis

“…However, at the nanoscale level, viewed by atomic force microscopy, fluorotic crystals had a significantly rougher surface than non-fluorotic crystals (Kirkham et al, 2001). The crystal surface roughness-likely the extremely small crystals seen at the surfaces of large crystals (Yanagisawa et al, 1989)-increased with higher fluoride levels in the drinking water (Chen et al, 2006). The first small (though not statistically significant) rise in roughness was noted at a drinking water level of 25 ppm fluoride (Chen et al, 2006), the minimal level that induces obvious fluorotic changes in the rat incisor.…”

Fluoride metabolism and fluorosis

“…46,47 Scanning and electron micrographic studies of fluorotic enamel have revealed alterations in crystallite morphology and crystal defects. 48 Increasing evidence of late has supported the hypothesis that excess fluoride in the extracellular fluids can result in delay of the cleavage and removal of amelogenin matrix proteins during enamel maturation. 49,50 An enzyme involved in hydrolysis of amelogenins may also be inhibited by fluoride.…”

Selective inhibition of collagen synthesis by fluoride in human pulp fibroblastsIn Vitro

“…Its positive effect against tooth decay has been well demonstrated by numerous epidemiological studies, but ingestion of excess fluoride (F) results in fluorosis with clinically observable mottled enamel. Histological features of fluorosed enamel have shown structural changes with hypomineralized zones and the presence of irregularly shaped crystals [1][2][3]. A decrease in the mineral content is accompanied by an increase in the organic content [4].…”