Influence of bioactive glass particle size in resin-based fissure sealants on the remineralization of adjacent enamel: an in vitro study

Abstract Background Bioactive glass (BAG)-modified fissure sealants may promote enamel remineralization, but the influence of BAG particle size remains unclear. This study aimed to compare the effects of micro-sized, nano-sized, and hybrid BAG particles incorporated into a resin-based fissure sealant on the remineralization of adjacent enamel using nanoindentation and SEM–EDS. Methods Forty-five sound human enamel specimens were randomly assigned to five groups (n = 9): unsealed negative control, conventional sealant, micro-BAG (15 wt%), nano-BAG (15 wt%), and hybrid BAG (7.5 wt% micro + 7.5 wt% nano). All specimens underwent artificial demineralization before the sealants were applied. Enamel adjacent to the sealant was assessed by nanoindentation (nanohardness, elastic modulus) before and after a 7-day pH-cycling regimen, and surface hardness recovery (%SHR) was calculated. Scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM–EDS) was performed descriptively on one specimen per group. Data were analyzed using paired t tests (within groups) and one-way ANOVA with Duncan's post hoc test (between groups) (α = 0.05). Results Mean nanohardness increased in all groups after pH cycling, but the increase was statistically significant only in the nano-BAG group ( P = 0.036). Nanohardness differed among groups after demineralization ( P = 0.044) and after pH cycling ( P = 0.031), with the unsealed negative control showing the highest values at both stages. No significant differences were found among groups in elastic modulus ( P = 0.106 and 0.056) or %SHR ( P = 0.820). SEM–EDS showed higher calcium content and Ca/P ratios in BAG-containing groups, with the highest values in the nano-BAG group; no statistical comparison was performed. Conclusions Within the limitations of this in vitro study, only the nano-BAG group showed a significant increase in enamel nanohardness after pH cycling, with no significant differences among the sealant groups. These preliminary findings support further investigation of nano-BAG–modified sealants, including larger samples, characterized fillers, and mechanical and ion-release testing.