Dental Fluorosis: Chemistry and Biology

Abstract

ABSTRACT:This review aims at discussing the pathogenesis of enamel fluorosis in relation to a putative linkage among ameloblastic activities, secreted enamel matrix proteins and multiple proteases, growing enamel crystals, and fluid composition, including calcium and fluoride ions. Fluoride is the most important caries-preventive agent in dentistry. In the last two decades, increasing fluoride exposure in various forms and vehicles is most likely the explanation for an increase in the prevalence of mild-to-moderate forms of dental fluorosis in many communities, not the least in those in which controlled water fluoridation has been established. The effects of fluoride on enamel formation causing dental fluorosis in man are cumulative, rather than requiring a specific threshold dose, depending on the total fluoride intake from all sources and the duration of fluoride exposure. Enamel mineralization is highly sensitive to free fluoride ions, which uniquely promote the hydrolysis of acidic precursors such as octacalcium phosphate and precipitation of fluoridated apatite crystals. Once fluoride is incorporated into enamel crystals, the ion likely affects the subsequent mineralization process by reducing the solubility of the mineral and thereby modulating the ionic composition in the fluid surrounding the mineral. In the light of evidence obtained in human and animal studies, it is now most likely that enamel hypomineralization in fluorotic teeth is due predominantly to the aberrant effects of excess fluoride on the rates at which matrix proteins break down and/or the rates at which the by-products from this degradation are withdrawn from the maturing enamel. Any interference with enamel matrix removal could yield retarding effects on the accompanying crystal growth through the maturation stages, resulting in different magnitudes of enamel porosity at the time of tooth eruption. Currently, there is no direct proof that fluoride at micromolar levels affects proliferation and differentiation of enamel organ cells. Fluoride does not seem to affect the production and secretion of enamel matrix proteins and proteases within the dose range causing dental fluorosis in man. Most likely, the fluoride uptake interferes, indirectly, with the protease activities by decreasing free Ca 2+ concentration in the mineralizing milieu. The Ca 2+ -mediated regulation of protease activities is consistent with the in situobservations that (a) enzymatic cleavages of the amelogenins take place only at slow rates through the secretory phase with the limited calcium transport and that, (b) under normal amelogenesis, the amelogenin degradation appears to be accelerated during the transitional and early maturation stages with the increased calcium transport. Since the predominant cariostatic effect of fluoride is not due to its uptake by the enamel during tooth development, it is possible to obtain extensive caries reduction without a concomitant risk of dental fluorosis. Further efforts and research are needed to settle the currently uncertain ...

The effect of non-fluoride factors on risk of dental fluorosis: Evidence from rural populations of the Main Ethiopian Rift

“…About half of the absorbed F − is quickly incorporated into developing bone and teeth, where nearly all of the body's F − is found, and the remainder is excreted in the urine (Cerklewski, 1997). Exposure to F − during enamel development causes a dose-related disruption of enamel mineralization resulting in anomalously large gaps in its crystalline structure, excessive retention of enamel proteins, and increased porosity of the teeth (Aoba and Fejerskov, 2002). The high prevalence of DF found in the study population is understandable: 89.9% of them live in communities having groundwater with F − concentration exceeding the WHO standard (N1.5 mg/l), and approximately 2/3 of these residents source water for drinking and cooking from the boreholes and dug wells which have the highest levels of naturally occurring chemical contaminants.…”

Fluoride concentrations in the water of Maringá, Brazil, considering the benefit/risk balance of caries and fluorosis

“…However, when fluoride is ingested during enamel mineralization, dental fluorosis can develop. 15 Thus, an adequate concentration of F in drinking water is necessary for water fluoridation to reach its maximum anticaries benefit with a minimum risk of fluorosis. 11 Data from this study showed that 83.7% of all of the water samples analyzed were within the range of best benefit and least risk, considering the new classification proposed by CECOL/USP.…”

Effects of fluoride and Aloe vera tooh gel in artificial white spot lesions in vitro

“…Dental fluorosis is a result of excessive fluoride ingestion during enamel development, which for the permanent teeth occurs in childhood between 2 to 8 years old 27 . The use of fluoride in preventive dentistry has been the most effective in carious lesions, but it also associated with the increasing prevalence of dental fluorosis in many countries.…”