Purpose: Evaluation of the effect of simulated brushing with toothpaste standardized by 10 wt. % nano-hydroxyapatite (n-HAp) for one year on the surface composition and nano-mechanical properties (hardness and elastic modulus) of human enamel.
Study design: 20 sliced human enamel/dentin slabs were divided into: control group (brushed with a commercial toothpaste) and test group (brushed with the same toothpaste with 10 wt. % n-HAp ~20 nm). Brushing was performed for one hour/day for 24 days. The nano-hardness and elastic modulus were measured (GPa) by the nano-indenter. SEM and EDXA were performed to study the morphology, thickness and the chemical composition of enamel surface. The Ca/P ratio was calculated (at. %). The data were statistically analyzed.
Results: Insignificant difference (P = 0.070) between the nanohardness values of the 2 groups was obtained. However, the elastic modulus of the control group was significantly lower than that of the test group (P = 0.019). SEM of the test group revealed the precipitation of n-HAp layer (~5 µm thick). The Ca/P ratios and the other minerals of the two groups were not significantly different.
Conclusions: Using dental products containing ≥10 wt. % n-AHp should be restricted to patients susceptible to demineralization; to avoid their detrimental effect on the elastic modulus that could be negatively reflected clinically on the mechanical behavior of the teeth.