Fluoride distribution in the enamel of the mesio-lingual cusps of pairs of erupted and unerupted third molars of man with a low fluoride background.

The enamel fluoride concentrations at different depths were determined at 5 different sites on the mesio-lingual cusps of 16 pairs of erupted and unerupted third molars. Six successive acid etchings were done on each of the 5 sites. The 16 subjects (18 to 33 years) were living continuously since birth in a low fluoride area (F less than 0.10 ppm). They did not take any systemic fluoride since birth nor did they practise any other anti-caries fluoride program than brushing their teeth once or twice a day with fluoride-containing dentrifrices with about 1,000 ppm fluoride. The fluoride level in the etch solution was measured with the use of an adapted fluoride selective electrode. Statistically significant differences (p less than 0.05) were found in the mean etch depth between the erupted and unerupted molars, to a depth of approximately 5 micron. The mean enamel fluoride concentrations of the erupted and unerupted molars also differed significantly to a depth of approximately 5 micron. There was no influence of fluoride from the oral environment on enamel levels of approximately 10 micron and deeper. Over an exposure period of 1 to 16 years, sixty percent more enamel fluoride (at a depth of approximately 2 micron) was found in the erupted enamel relative to the unerupted enamel (with a low background fluoride) as a result of tooth brushing with fluoride-containing dentifrices. More enamel fluoride was found near the incisal edge than near the cervical margin of 14 of the 16 subjects independently of the age of the subjects.