Remineralization of early caries lesions by calcium hypophosphite in vitro: a surface microhardness study

This in vitro study used a pH cycling model to compare the caries remineralizing efficacy of toothpaste formulations containing calcium hypophosphite (CaP), hydroxyapatite (HAP), or sodium fluoride (NaF).

Bovine enamel blocks with plaque-induced initial caries lesions were randomized (n = 30/group) to toothpaste formulations containing 1% CaP, 20% HAP, 1% CaP+20% HAP, or 1450 ppm fluoride provided as NaF. Lesion-bearing samples were subjected to a 14-day remineralization using a pH-cycling model with daily regimen of three 2-min applications of toothpaste slurry (1:3 toothpaste: water), one 2-h acid exposure, and storage in artificial saliva for the rest of the day. Remineralization was quantified as change in surface microhardness (SMH) of each sample measured before and after toothpaste treatment and expressed as percent remineralization (%Rem). Statistical analyses included paired t tests for within-group changes and one-way ANOVA with Tukey's post hoc tests for between-group comparisons (α = 0.05).

All groups exhibited significant (paired t test, p < 0.001) increase in SMH from baseline, indicating remineralization. Combining CaP and HAP achieved significantly (ANOVA/Tukey's, p < 0.001) greater %Rem (89.7 ± 3.3) when compared with CaP alone (75.4 ± 5.5), HAP alone (62.4 ± 4.8), or NaF alone (60.3 ± 7.8). While %Rem achieved with CaP alone was significantly (p < 0.001) greater than that of HAP and NaF, there was no significant difference in %Rem between HAP and NaF.

This in vitro study demonstrates that CaP alone, and in combination with HAP, increases enamel surface microhardness, confirming that CaP-based formulations are efficient strategies for the remineralization of early caries lesions.