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 fluorosis requires children aged 12–13 in whom the premolars and second molars have erupted. The mottled enamel first drawn to McKay’s attention in Colorado is moderate and severe fluorosis (Fig. 16.4).

The level of fluorosis in an individual is determined by observing the buccal surface of each tooth and classifying it as one of the following: Normal (score 0) Enamel presents the usual translucent, appearance. The surface is smooth, glossy, and usually of a pale creamy white color; Questionable (score 1) The enamel has slight aberrations from normal translucency, ranging from a few white flecks to occasional white spots; Very mild (score 2) Small, opaque, paper-white areas scattered over less than 25% of the tooth surface or a premolar or molar tooth showing no more than 2 mm of white opacity at the tip of the cusps; Mild (score 3) White opaque areas are discontinuous or a continuous white opacity affects less than 50% of the tooth surface (Central incisors in Fig. 16.1b); Moderate (score 4) More than 50% but not all of the enamel surface is affected with a continuous white opacity and little or no brown is present (Fig. 16.4); Severe (score 5); All of the enamel surface displays a continuous white opacity or more than half of the tooth surface is stained brown and surfaces are subject to mild attrition (Figs. 16.1a and 16.4). An individual is assigned a number (0 through 5) which represents two or more teeth with the greatest severity score. The index of fluorosis is the mean of these individual scores within a community.

The greater the fluoride content of the public water supply, the greater is the index of fluorosis. At less than 1 ppm fluoride in the drinking water, the index of fluorosis in the community is essentially zero (no fluorosis) and increases to severe at 8–10 ppm fluoride in the drinking water. Fig. 16.5 illustrates how the severity of fluorosis changes with amount of fluoride in the community water supply and also the average number of decayed, missing, and filled teeth (DMFT, Sect. 15.1.1). The subjects were children aged 12–14 years in various US cities and communities and their DMFT is compared in Fig. 16.5 with the ppm fluoride in their water supply.

If the water supply had no fluoride, the population displayed 6–8 DMFT. As the fluoride concentration increased to 1 ppm, the mean DMFT of the population decreased by about 50%, but the index of fluorosis remained well below 1. Increasing the fluoride above 1 ppm slightly decreased the DMFT further, but markedly increased the prevalence of fluorosis. The line of decreasing fluorosis intersects with the line of decreasing caries at just over 1 ppm fluoride as seen in the center of Fig. 16.5.