Toothpaste Fluoride Concentration Effect on Enamel and Dentine De-remineralization

Objectives: There is evidence that the effect of fluoride toothpaste on enamel caries is concentration dependent and that for root caries a high fluoride toothpaste (5,000 ppm F) should be recommended instead of the conventional ones (1,000-1500 ppm F). However, the relative effect of fluoride concentration on inhibition of demineralization of sound enamel and root dentine, and on enhancement of remineralization of these demineralized substrates has not been explored.
Methods: A double-blind, crossover, in situ study of four phases of 14 days each was conducted. Volunteers (n=18) wore a palatal appliance containing slabs of enamel and root-dentine, either sound or presenting incipient caries lesions, whose surface hardness (SH) was previously determined. Dental biofilm was allowed to accumulate on slabs surfaces and, while the sounds labs were exposed to 20% sucrose 8x/day, the carious ones were subjected 3x/day, simulating respectively conditions of caries progression (demineralization) or regression (remineralization). Twice a day, the volunteers used and subjected the slabs to silica-based toothpastes containing 0, 1,100 ppm F or 5,000 ppm F, as NaF. At the end of each phase SH was again assessed and the percentage of hardness of loss (%SHL) in the initially sound slabs, and of hardness recovery (%SHR), in the initially carious ones, was calculated, as indicator of de- and remineralization, respectively. Data were analyzed by linear regression.
Results: %SHL decreased linearly (p<0.001) with the increasing fluoride concentration in toothpaste (from 0 to 5000 ppm F), either for enamel (55.2±22.9; 35.4±17.7; 25.4±16.3) or dentine (50.2±11.4; 34.6±11.2; 21.3±17.7), respectively. %SHR increased linearly (p<0.001) only for enamel (13.6±9.1; 21.2±12.8; 30.2±17.7, respectively).
Conclusions: The findings suggest that high fluoride toothpaste may contribute to inhibit the demineralization of either enamel or root dentine but its effect on the enhancement remineralization may be relevant only for enamel.