Whitening Efficacy and Enamel Protection of 35% Hydrogen Peroxide Solution Containing Alkaline-Substituted Bioactive...

This study aimed to investigate the whitening efficacy and enamel surface protective effects of 35% hydrogen peroxide (HP) solutions modified with alkali-substituted bioactive glasses (BAGs). Three alkali BAG formulations (K-, Li-, and LiK-based) were added to 35% HP at concentrations of 0.1, 1.0, and 10.0 wt %. The control group contained HP without BAG or distilled water (DW). The pH of each solution was monitored. Discolored bovine enamel specimens were treated thrice with each solution (20 min/session). Enamel surface color change (ΔE) was assessed by spectrophotometry, while surface gloss, roughness (Ra), and Vickers microhardness were also measured. Morphological alterations were examined by scanning electron microscopy (SEM). Statistical analysis was performed using one-way analysis of variance with Tukey's post hoc test (α = 0.05). All BAG-modified groups showed significantly higher pH values than HP alone (p < 0.05), with K- and LiK-based formulations producing the greatest pH increases. Except for Li 0.1%, the ΔE values of all formulations were statistically comparable to those of HP (p > 0.05), indicating no loss of whitening efficacy. BAG addition significantly improved gloss and microhardness and reduced roughness compared with HP alone (p < 0.05). At concentrations ≥ 1%, enamel surface properties were restored to levels similar to those of DW (p > 0.05). SEM revealed progressively smoother enamel surfaces with increasing BAG concentration. In conclusion, incorporating alkali-substituted BAGs into 35% HP preserved bleaching efficacy while markedly reducing enamel surface damage; concentrations ≥ 1% showed the most consistent protective effects. High-concentration HP bleaching may compromise enamel integrity despite its whitening effectiveness. The addition of alkali-substituted BAGs effectively buffered the bleaching environment and promoted surface protection without impairing whitening efficacy. This approach represents a promising adjunct for safer and more predictable in-office bleaching procedures.