Remineralization Characteristics of Superficial and Advanced Enamel Artificial Caries

Objectives: The aim of this in vitro study was to evaluate the role of high-fluoride dentifrice on remineralization characteristics of superficial and advanced enamel artificial caries lesions.
Methods: Bovine enamel specimens with either one lowly [L] or highly [H] pre-demineralized (pH 4.95; 21 days) artificial caries lesions were prepared. Specimens with a mean ΔZ_baseline,L (95% CI) of 5,120 (4,995; 5,245) vol%×µm for L lesions and a mean ΔZ_baseline,H of 8,187 (8,036; 8,339) vol%×µm for H lesions were selected and randomly allocated to twelve groups (n=20). Treatments during pH-cycling (28 days and 6x60 min demineralization/day) were: brushing 2x/day with: fluoride-free (0 ppm F^- [L₀/H₀]); 1,100 ppm F^- [L₁₁₀₀/H₁₁₀₀]; 2,800 ppm F^- [L₂₈₀₀/H₂₈₀₀]; 5,000 ppm F^- [L₅₀₀₀/H₅₀₀₀); 5,000 ppm F^- + glycerin [L_{5000+glycerin}/H_{5000+glycerin}]; and 5,000 ppm F^- + TCP [L_5000+TCP/H_5000+TCP] containing dentifrices. Dentifrice slurries were prepared with deionized water (1:3wt/wt). After cycling specimens presenting lesion surface loss were discarded and for the remaining 202 specimens new transversal microradiography (TMR) analyses (ΔZ_pH-cycle/LD_pH-cycle) were performed. Changes in mineral loss (ΔΔZ=ΔZ_baseline-ΔZ_pH-cycle) and lesion depth (ΔLD=LD_baseline-LD_pH-cycle) were calculated.
Results: Significant differences for ΔΔZ could be found between L₀, L₁₁₀₀ and L₅₀₀₀ as well as H₀, H₁₁₀₀ and H₂₈₀₀/H₅₀₀₀ (p≤0.049; Bonferroni post-hoc test). The correlation between ΔΔZ and F^- was moderate for lowly and strong for highly demineralized specimens (r_L=0.591; p_L<0.001; r_H=0.746; p_H<0.001), indicating a fluoride dose-response for L and H. In general H led to a significant higher ΔΔZ compared with L, except for 0ppm F^- (p≤0.003; two-tailed-t-test). After pH-cycling a second lesion front could only be observed in specimens of H₅₀₀₀ and H_5000+TCP.
Conclusions: For both baseline substrate conditions a dose-response could be revealed. Furthermore, remineralization characteristics of enamel directly depended on baseline mineral loss.