Objectives: To determine the effect of dentifrice fluoride ion concentration on remineralization of eroded enamel in-situ, across the range 0-1426 ppm fluoride.
Methods: This was a single-centre, four-way, randomized, crossover study involving four Experimental sodium fluoride-silica dentifrices, containing 0, 250, 1150 or 1426 ppm fluoride. The study was conducted dental examiner‑, subject- and analyst-blind. Subjects wore a palatal appliance holding 8 polished bovine enamel specimens, with erosive lesions created by 25 minutes exposure to grapefruit juice. They brushed the buccal surfaces of their teeth with 1.5 g test dentifrice for 25 seconds, followed by 1 minute swishing around the mouth to ensure specimen exposure to the slurry. Subjects expectorated, and then rinsed with 10 mL water for 10 seconds.
After a single 4-hour intra-oral remineralization period, specimens were re-challenged in-vitro with grapefruit juice. Enamel surface microhardness, measured at each stage (pre-experimental, post-initial acid-exposure, post-remineralization, and post-second acid-exposure), was used to calculate surface microhardness recovery (SMHR) and relative erosion resistance (RER). Enamel fluoride uptake (EFU) was also measured.
Results:
Dentifrice F concentration (ppm) | SMHR, % | RER, % | EFU, µg F/cm2 |
0 | 21.14 (1.511) | -71.35 (3.429) | 1.47 (0.080) |
250 | 25.29 (1.695) | -50.30 (2.482) | 2.09 (0.080) |
1150 | 28.83 (1.443) | -39.49 (2.522) | 3.07 (0.091) |
1426 | 31.08 (1.497) | -38.88 (2.818) | 3.13 (0.097) |
All values are mean ± standard error. SMHR, RER and EFU showed highly significant linear dose-response relationships with dentifrice fluoride concentration (p<0.0001). Within each measure, values for different fluoride concentrations were resolved from each other (p<0.05), except the 1150 and 1426 ppm concentrations.
Conclusion: This study reports, for the first time across the range 0-1426 ppm fluoride ion, that increasing dentifrice fluoride concentration can progressively increase in-situ remineralization of early enamel erosive lesions after toothbrushing. Furthermore, increasing fluoride concentration across this range can also progressively increase dietary acid-resistance of the newly formed mineral.