Aluminum uptake and inhibition of enamel dissolution by sequential treatments with aluminum solutions

The effects of sequentially applied solutions containing aluminum (Al) on enamel uptake and inhibition of acid dissolution were investigated. Following 10 consecutive 5-min treatments with seven Al solutions varying in concentration from 0.15 to 2.0 mmol/l, the subsequent acid dissolution of enamel was progressively reduced from 0 to over 70%. Teeth treated with 1.5 mmol/l Al from 1 to 30 consecutive 5-min periods demonstrated a stepwise increase in the reduction of enamel acid dissolution ranging from about 10 to 90%. Following the same treatment regimen, the amount of Al deposited in the enamel varied from 2,500 ppm after a single 5-min application to approximately 9,000 ppm after 20 or 30 consecutive treatments. These experiments showed that teeth repeatedly exposed to low concentrations of Al solutions (i.e. < 2 mmol/l) progressively accumulated significant amounts of Al in the surface enamel, which was associated with a concomitant decrease in the acid dissolution rate of enamel.