The prevalence of enamel mottling in optimal and low fluoride areas of the West Midlands was studied in March 1989 using the Al-Alousi index and the TF index. A total of 600 children aged 8-10 years, in three groups of 200 each, formed the study group. Significantly more mottling was found in the optimal fluoride area, according to both indices, although the TF index demonstrated the difference more clearly. Social class had no effect upon the prevalence of mottling in the optimal fluoride area.
Hamdan M, Rock WP., Community Dent Health. 1991 Jul;8(2):111-9. The prevalence of enamel mottling on incisor teeth in optimal fluoride and low fluoride communities in England.