Remineralization efficacy of nano-hydroxyapatite and potassium nitrate formulations on demineralized enamel and dentin: An <i>in vitro</i> surface hardness and EDX-SEM study

The present in vitro study aims to evaluate both the remineralizing and desensitizing potential of experimental dentifrices combining 2.5% and 5% nano-hydroxyapatite (nHAp) with 5% potassium nitrate. Twenty-four caries-free human teeth were prepared, and surface microhardness was measured before and after 96 h of demineralization. The gels were applied twice daily for 7 days, followed by post-treatment hardness assessment. Elemental composition (Ca, P, K, Ca/P ratio) was analyzed using energy-dispersive X-ray spectroscopy (EDX), and surface morphology was examined via scanning electron microscopy (SEM). Demineralization significantly reduced hardness and mineral ratios (p<0.05). Both formulations improved hardness and partially restored mineral levels. Including tests conducted within this study, dentin exhibited complete recovery, while enamel showed partial recovery. No statistically significant difference was found between the 2.5% and 5% nHAp concentrations. These findings suggest that both concentrations are effective, and increasing nHAp beyond 2.5% does not yield additional benefit, supporting their use as dual-action agents for remineralization and hypersensitivity relief.