Efficacy of calcium hypophosphite toothpaste in remineralizing initial caries in vitro

The effectiveness of hydroxyapatite (HAP) toothpastes in remineralizing initial caries and preventing caries development has been well-established. Calcium hypophosphite (CaP) is a calcium compound that readily dissolves in water providing calcium ions, and as such can promote remineralization. The present study investigated the potential of CaP to enhance the caries remineralizing capacity of HAP-containing toothpaste.

120 bovine tooth blocks were randomly assigned to four toothpaste groups (30/group) containing either 20% HAP, 20% HAP + 1% CaP, 1% CaP, or 1450 ppm fluoride (NaF). Blocks were subjected to 4-day demineralization by plaque growth in a mixed-species microbial caries model for development of initial caries lesions. The lesion-bearing blocks were subjected to remineralization by daily pH cycling consisting of three 2-minute toothpaste treatments, a 2-hour acidic challenge, and then storage in artificial saliva for the rest of the time for 14 days. Toothpastes were homogenized with water (1 toothpaste:3 water) and applied as slurry. Remineralization was measured as a change in mineral density (MD) of the lesions before and after treatment, measured using microcomputed tomography (µCT). Percentage change in MD (percentage remineralization [%Rem]) in each group was calculated. Intra-group (paired t-test) and inter-group (ANOVA/Tukey's test) comparisons were conducted (α = 0.05).

Paired t-test indicated significant difference (p<.001) between pre-treatment and post-treatment MD in all groups demonstrating remineralization. Intergroup comparison based on their %Rem using ANOVA/Tukey's test showed that 20% HAP + 1% CaP (95.7 ± 3.26) had significantly (p<.001) higher %Rem than 1450 ppm fluoride (67.3 ± 7.81), 20% HAP (69.4 ± 4.79), and 1% CaP (80.4 ± 5.49). All other compared groups, except 1450 ppm fluoride vs. 20% HAP, differed significantly (p<.001).

The present study shows that the addition of CaP to a HAP-containing toothpaste significantly enhanced the effectiveness of the HAP to remineralize initial caries. It further demonstrates that CaP alone effectively remineralizes caries lesions.