A guide to fluoride

Fluoride can be taken into the crystalline structure of enamel, to form fluorapatite crystals replacing the normal hydroxyapatite crystal structure. Fluorapatite can resist acid attack to a greater degree and thereby reduces the solubility of enamel in acid. Fluoride also has an inhibitory effect on the feeding rate of oral bacteria, which produce fewer, weaker acids and polysaccharides to initiate carious attack.

Enamel, formed in the presence of fluoride, tends to have more rounded cusps and fissure pattern, but the effect is small. Discontinuation of systemic fluoride results in an increase in caries therefore pre-eruptive effects must be limited. It is, therefore, incorrect to suggest that fluoride is only beneficial to children, or that it must be incorporated into developing enamel in order to have an effect. Excessive fluoride intake during the period of tooth formation will result in the eruption of teeth with fluorosed or mottled enamel. This may range from white lines in enamel to chalky opaque enamel, which turns brown or black after eruption. The enamel may even break apart. This most severe form is unusual in the UK. The severity depends on the amount of fluoride ingested, its timing and individual susceptibility factors, such as body weight. For upper central incisors, the risk is considered to be greatest for children between the ages of 15-30 months. Ingestion of fluoride after the eruption of the 6s will have little input on tooth development, because the coronal development of the anterior teeth is complete. Efforts to minimise the ingestion of fluoride needs to be focused at the under sevens. The underlying histological feature of fluorosed enamel is an increase in enamel porosity. Opacities in enamel could also be due to childhood infections, genetic causes or trauma.