Effect of Hydrogen Peroxide Bleaching on Color Stability and Microhardness of Alkasite Restorative Materials: An In Vitro Study

Abstract

Introduction: High-concentration hydrogen peroxide (HP) bleaching agents are widely used in dental practice but may compromise the optical and mechanical properties of restorative materials. This in vitro study evaluated the impact of 40% HP bleaching on the color stability and microhardness of alkasite restorative material under different curing modes. Methods: Sixty discs of alkasite restoration (Cention N) were prepared and divided into two groups: chemical-cured (n=30) and dual light-cured (n=30). Color coordinates (L, a, b*) were measured using spectrophotometry, and microhardness was assessed using Vickers testing before and after three consecutive 20-minute bleaching sessions with 40% HP. Data were analyzed using paired t-tests and one-way analysis of variance (ANOVA) with post-hoc Tukey tests (P < 0.05). Results: Bleaching significantly altered alkasite color with an overall change of ΔE = 1.77 ± 1.45 (P < 0.001), exceeding the clinically acceptable threshold of ΔE = 1.0. Chemical-cured specimens showed significantly greater color change (ΔE = 2.22 ± 1.81) than light-cured specimens (ΔE = 1.31 ± 0.74, P = 0.015). Microhardness decreased significantly in both groups after bleaching (P < 0.001), with chemical-cured specimens exhibiting greater reduction. Conclusions: High-concentration HP bleaching significantly compromises both color stability and microhardness of alkasite restorations, with chemical-cured specimens being more susceptible to these changes than light-cured specimens. These findings suggest that high-concentration bleaching may adversely affect alkasite restoration longevity and aesthetic outcomes.