Enamel fluorosis

The primary adverse effects associated with chronic, excess fluoride intake are skeletal, and dental or enamel, fluorosis. Other effects, including hypersensitivity reactions, renal insufficiency, immunological effects, possible association with repetitive strain injury, birth defects and cancer have been observed and discussed [17,41-45]. 

Dental or enamel fluorosis is an irreversible dose-response effect caused by fluoride ingestion during the pre-eruptive development of teeth. The pre-eruptive maturation of crowns of the anterior permanent teeth, which are of most concern aesthetically, is complete and, together with the risk of fluorosis, is over by the age of 7-8 years [46,47]. After the enamel has completed its pre-eruptive maturation, it is no longer susceptible. Therefore, fluoride intake up to the age of 7-8 years is of most interest. Although it is usually the permanent teeth that are affected, occasionally the deciduous teeth may be also involved. 

This chapter describes how individuals with severe enamel fluorosis (mottled tooth enamel) became associated with fluoride in the public water supply and protection from dental caries. A comparison of caries experience with the fluoride content of public water supplies and enamel fluorosis in adolescents indicated that 1 pg fluoride/mL (1 part/million) in the water provides caries protection with minimal enamel fluorosis (sect. 1). One mechanism is the spontaneous isomorphic replacement of apatite s hydroxide anions with fluoride, which reduces enamel solubility. A second is fluoride-mediated inhibition of enolase, which retards bacterial acid production at teeth surfaces. These findings led to the use of fluoride in toothpastes, which provides better protection from caries at tooth surfaces than water fluoridation alone (sect. 2). The chapter concludes with a discussion of potentially harmful effects of fluoride ingestion (sect. 3). 

Mottled Enamel Is Moderate to Severe Enamel Fluorosis... 

Fluoride is both incorporated into enamel crystals and also affects the enzymes involved in enamel formation (Sect. 16.2.2), causing mottled enamel, a severe example of enamel fluorosis. Enamel fluorosis is evident as specks or white flecks on the enamel surface (Fig. 16.2b). In 1941, the public water supply of Aurora (IL) contained 1.2 ppm of fluoride (F), but only 5% of teeth exhibited fluorosis, mostly premolars and second molars. A sensitive index of... 

The fluoride ion can replace the hydroxide ion in a crystal without significantly altering its structure, an isomorphous ion replacement. Fluoride also affects the enzymes involved in enamel formation, causing mottled enamel, a severe example of enamel fluorosis. White opaque patches on the normally translucent enamel indicate mild fluorosis. Fluorosis is measured on a grade of 0-5 where 1 through 3 indicate an increased cover of opaque white patches on the tooth surface, and 4 and 5 indicate an increased mottling. The two worst affected teeth make up an individual s score. The community s index of fluoridation is the mean score for all individuals. As the natural or artificial fluoride concentration of the water supply increases to 1 ppm, the mean number of cavities in 10-12 year-old children decreases from 7 to 3. Above 1 ppm fluoride, caries does not decrease much more, but the index of fluorosis increases markedly. This is the reason why public water supplies are fluoridated to only 1 ppm and not more or less. 

F excess Baltic Sea States, Belarus, Moldova, Central Yakutia, Kazakstan Excessive content of F in natural waters, > 1.0-1.5 ppm. Low content of F in soil and plants Tooth enamel dystrophy. Fluorosis and spotted teeth of human and animals... 

Under neutral conditions, fluoride is also able to induce nucleation and growth of apatite crystals without the involvement of OCP [72]. This requires fluoride concentrations of 0.5 ppm or higher, which are rarely achieved in vivo except in cases where fluorosis may result. It is significant that in severe cases of fluorotic enamel, ultra-structural studies [73] have shown the occurrence of a proliferation of apatite nuclei, suggesting that the presence of fluoride may act to encourage precipitation of crystals of fluorapatite. 

Fluorosis affects the enamel of the tooth, causing it to become hypominera-lised. This is detected as visual changes in the opacity, and it is only in extreme cases that this leads to an adverse appearance as mottling of the tooth surface [86]. The severity of the discolouration depends on the dose of fluoride, its duration and timing of consumption. 

The risk of fluorosis is only of concern for children below about 8 years of age, because enamel can no longer be affected once pre-eruptive maturation has occurred [89]. As far as cosmetic effects are concerned, the critical age is somewhat younger because at this age the central incisors are undergoing development, and hence are at a stage that makes them susceptible to fluorosis. For children at the age likely to be affected, the main sources of fluoride are drinking water, processed food and beverages, toothpaste and other dental products (i.e., tablets or drops). 

In its mildest form, fluorosis appears on the enamel surface as chalky, lace-like marks, and these may not be apparent to the casual observer [90]. As severity... 

In general, moderate and severe fluorosis is rare. However, mild fluorosis has been detected at significant levels, for example, in 26% of subjects in one recent study [93]. However, the mildness of the fluorosis detected is associated with only very slight changes in the appearance of the teeth, which suggests that, even at these levels, it is not a major public health problem. Nonetheless, it is appropriate to ensure that parents or guardians of children continue to receive sound advice on safe levels of fluoride for those in their care to be exposed to and, since the cariostatic effect of fluoride is known to occur well after enamel formation during tooth development, treatment to reduce caries should concentrate on those measures that carry the lowest possible risks of fluorosis [91]. 

T. Yanagisawa, S. Takuma, FI. Tohda, O. Fejerskov, R.W. Fearnhead, Fligh resolution electron microscopy of enamel crystals in cases of human dental fluorosis, J. Electron Microsc. 38 (1989) 441-448. 

Fig. 2. Teeth demonstrating fluorosis. A high level of dietary fluoride has resulted in much of the enamel becoming opaque in patches, giving a mottled appearance. (Reprinted with permission from [48]. Copyright 2002 Mosby International Limited.) (See Colour Plate Section at the end of this book.)...

Ingestion > inhalation. At low levels mottling of tooth enamel. At high levels fluorosis—includes wide variety of health problems such as hyperparathyroidism, calcification of soft tissues, interference with collagen formation, severe skeletal deformity. 

Fluoride poisoning can occur after chronic ingestion of excessive amounts of fluoride, causing osteosclerosis and dental fluorosis (mottled enamel), due to accidental ingestion of fluoride mixtures during dental treatment (7,8), or after ingestion of insecticides or rodenticides containing fluoride salts. 

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