Efficacy of Fluoride Toothpaste Fortified With Micro‐ and Nano‐Hydroxyapatite on Remineralization and Surface Roughness of Synthetic Enamel

Abstract

ABSTRACT Objectives To evaluate the remineralization efficacy and surface effects of 1450 ppm fluoride toothpaste fortified with synthetic hydroxyapatite (Syn‐HAP) of varying particle sizes and concentrations on synthetic enamel. Material and Methods Nano‐sized Syn‐HAP (nanoSyn‐HAP) was synthesized via a mechanochemical process and characterized using X‐ray diffraction (XRD) and transmission electron microscopy (TEM). Sixty disc‐shaped synthetic pellets underwent artificial caries induction and were randomly divided into five groups: Untreated (negative control), commercial 1450 ppm fluoride toothpaste (FT), FT plus 5% micrometer‐sized Syn‐HAP (FT+5mHAP), FT plus 5% nanoSyn‐HAP (FT+5nHAP), and FT plus 10% nanoSyn‐HAP (FT+10nHAP). Specimens then underwent a 15‐day pH cycling regimen with twice‐daily treatments. Knoop microhardness was evaluated at baseline, post‐caries induction, and post‐treatment; surface roughness and scanning electron microscopy (SEM) were assessed at baseline and post‐treatment. Data were analyzed using ANOVA and Bonferroni post‐hoc tests (p < 0.05). Results XRD confirmed a pure hydroxyapatite phase, and TEM indicated that 93% of particles were smaller than 50 nm. All toothpaste‐treated groups exhibited significant microhardness recovery versus the untreated group (p < 0.05), with no significant differences among them. The untreated and FT groups showed significantly increased roughness after 15 days (p < 0.01), whereas all Syn‐HAP groups maintained smoothness comparable to baseline, with significantly lower roughness than FT (p < 0.01). SEM corroborated these findings, revealing smoother surfaces with particle integration in the Syn‐HAP groups. Conclusions Under the conditions of this in vitro study, supplementing 1450 ppm fluoride toothpaste with Syn‐HAP produced surface microhardness recovery that did not differ significantly from that of standard fluoride toothpaste, while significantly improving the preservation of surface smoothness. Syn‐HAP‐fortified formulations therefore offer a promising approach for caries management, combining effective surface hardening with superior surface integrity, although confirmation in in situ and in vivo settings is required.