Mechanism and Timing of Fluoride Effects on Developing Enamel

Abstract

Fluoride appears to specifically interact with mineralizing tissues, causing an alteration of the mineralization process. In enamel, fluorosis results in a subsurface hypomineralization. This hypomineralized enamel appears to be directly related to a delay in the removal of amelogenins at the early-maturation stage of enamel formation. The specific cause for this delay is not known, although existing evidence points to reduced proteolytic activity of proteinases that hydrolyze amelogenin. This delay in hydrolysis of amelogenins could be due to a direct effect of fluoride on proteinase secretion or proteolytic activity, or to a reduced effectiveness of the proteinase due to other changes in the protein or mineral of the fluorosed enamel matrix. The formation of dental fluorosis is highly dependent on the dose, duration, and timing of fluoride exposure. The early-maturation stage of enamel formation appears to be particularly sensitive to the effects of fluoride on enamel formation. Although the risk of enamel fluorosis is minimal with exposure only during the secretory stage, this risk is greatest when exposure occurs in both secretory and maturation stages of enamel formation. The risk of fluorosis appears to be best related to the total cumulative fluoride exposure to the developing dentition.

No Relationship between Subchronic Fluoride Intake and DNA Damage in Wistar Rats

“…Taking into account the fluoride consumed with the food per day per animal, the negative control group ingested 0.17 mg; the group exposed to 7 ppm of NaF in drinking water ingested 0.25 mg; in the group exposed to 100 ppm of NaF, the total amount of fluoride ingested was 1.34 mg. After 6 weeks of NaF intake by rats, the group exposed to 100 ppm of NaF showed symptoms of dental fluorosis [Denbesten and Crenshaw, 1984;Denbesten, 1999], while the negative control and the group exposed to 7 ppm of NaF did not. Thus our experimental design using rat food containing fluoride is feasible for studying dental fluorosis as well as for evaluating the effects of fluoride on the genetic apparatus in low and toxic doses.…”

“…Since rat metabolism is 10 times faster than human metabolism in respect to fluoride [Smith et al, 1993], we administered 7 ppm of NaF in drinking water. On the other hand, the high dose (100 ppm of NaF) was defined as the dose producing signs of toxicity in the form of clinically detectable dental fluorosis, as previously described by other studies using this experimental design for studying dental fluorosis in rats [Denbesten and Crenshaw, 1984;Smith et al, 1993;Denbesten, 1999].…”

Ultrastructural morphometric analysis of ameloblasts exposed to fluoride during tooth development

“…According to some authors, high doses of fluoride may cause dilated mitochondria in ameloblasts of rat incisor (Kruger 1968;Mornstad and Hammarstrom 1978), and the distention and accumulation of secretion material in the rough endoplasmic reticullum (RER) (Kruger 1968). Others have mentioned that excess fluoride may cause accumulation of clear vacuoles (Walton and Eisenmann 1974), reduction of calcium levels in the enamel organ (Eisemann et al 1982), decreased secretion of lysosomal enzymes (Josephen and Fejerskov 1977), fewer bands of modulating ameloblasts, altered rate of ameloblast modulation and slower removal of enamel matrix (Denbesten 1999). As a result, and because of inappropriate in vivo evidence, the aim of this study was to investigative whether fluoride can induce damage in ameloblasts of rat incisor undergoing secretory and maturation phases of amelogenesis using ultrastructural analysis.…”

“…However, it has been postulated that excess fluoride may result in chronic injury to reproductive system cells (Ghosh et al 2002), some cellular components (Matsuo et al 1998), and the nervous system (Chen et al 2002), and may promote disturbances in enamel development known as dental fluorosis, which is clinically characterized as enamel hypomineralization zones (Denbesten et al 2002;Bartlett et al 2005). Fluorosed enamel has a greater organic content than normal enamel, a factor which may be due to delay in the removal of enamel matrix performed by maturation ameloblasts (Denbesten 1999;Robinson et al 2004).…”

Effects of silver nanoparticles on the bonding of three adhesive systems to fluorotic enamel

“…The adverse effect of excessive exposure to fluoride is dental fluorosis, which is a permanent hypo-mineralization in the subsurface of enamel, characterized in its mildest form by small, clearly visible, white flecks found on the cusp tips and on facial surfaces of permanent dentition 2) . Fluorosis is mostly found on permanent teeth surfaces ranging from obvious white opaque areas (moderate form) to darkly stained and pitted enamel (severe form) 3) . The effect of fluoride on forming enamel results in several changes, these changes in the structure of enamel involve increased porosity, higher protein levels, and lower amounts of minerals and, in severe cases, the formation of a pitted surface 4) .…”