Evaluation of low fluoride toothpaste using primary enamel and a validated pH-cycling model

Aim To develop and validate pH-cycling model for primary enamel, which was then used to evaluate the anti-caries potential of fluoride toothpastes. Design Human primary enamel slabs were subjected to pH-cycling model for 10 days and maintained for 6 h in demineralizing solution and 18 h in remineralizing solution daily. Twice/day, the slabs were treated. To validate it, the treatments were water or solutions containing 62.5, 125, 250, and 375 μg F/mL. Commercial toothpastes containing no fluoride, 500, 1100, and 1450 μg F/g were evaluated. Demineralization was assessed by percentage of surface hardness loss (%SHL) and cross-sectional hardness (ΔS). Fluoride dose–response effect was analysed by quadratic regression and the effects of toothpastes by Tukey's test. Results Dose–response effect was found between fluoride concentration and %SHL (R2 = 0.7047; P < 0.01) or ΔS (R2 = 0.4465; P < 0.01). %SHL and ΔS (mean ± SD) for the group treated with 500 μg F/g toothpaste was 36.6 ± 8.0 and 6298.5 ± 1221.3, respectively, which were significantly higher than those treated with 1100 (25.2 ± 8.7; 4565.7 ± 1122) and 1450 μg F/g (24.2 ± 5.2; 2339.1 ± 879.7) toothpastes. Conclusion The developed pH-cycling model may be used to evaluate and compare the anti-caries potential of toothpaste formulations with low fluoride concentration because it presents dose–response effects on the reduction of primary enamel demineralization.