Effects of hydroxyapatite-containing oral care products on phosphoric-acid-etched enamel micro-morphology: Findings from erosion-relevant in vitro and in situ environments.

OBJECTIVES

To investigate whether hydroxyapatite (HAP)-containing oral care products induce micro-morphological changes on phosphoric-acid-etched enamel surfaces indicative of mineral precipitation, and to determine how such changes depend on the surrounding environment.

DESIGN

Human enamel slabs from previously unerupted teeth were flattened, polished, split into reference and test halves, and phosphoric-acid etched. HAP-containing toothpastes and mouth rinse, active-agent-free toothpaste, and fluoride/stannous (F/Sn) controls were applied in three environments: a mineral-free in vitro environment, a mineral-containing in vitro environment, and an in situ environment. Samples were examined by scanning electron microscopy, and representative structures were analysed by energy-dispersive X-ray spectroscopy. Micro-morphologies were classified as covered/rounded prism heads, reticular structures, or mucous structures.

RESULTS

In the mineral-free environment, only limited changes were observed, mainly covered/rounded prism heads, with no indication of mineral precipitation. In the mineral-containing environment, reticular structures consistent with precipitate-like deposits were found after some, but not all, formulations. Their occurrence was not related specifically to HAP, as they were also observed after the negative-control toothpaste. In the in situ environment, no reticular structures were detected; instead, covered/rounded prism heads and mucous structures predominated, with pronounced inter-individual variation.

CONCLUSION

HAP-containing oral care products did not show micro-morphological effects indicative of specific mineral deposition in any environment. The findings suggest that formulation-environmental interactions, potentially involving excipient-related effects, may influence the formation or persistence of precipitate-like surface structures.