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Assessing the Effects of In-office Bleaching Agents on Mechanical Behavior, Surface Morphology, and Color Stability
Abdullah Alshehri1, Rania E Bayoumi1,2, Ali Robaian1
1Department of Conservative Dentistry, College of Dentistry, Prince Sattam Bin Abdulaziz University, Al Kharj, Saudi Arabia.
Objectives:
The increasing demand for aesthetic dental treatments has led to widespread use of resin composites and in-office bleaching procedures. This study evaluated the effect of 35% hydrogen peroxide bleaching on the surface roughness, microhardness, wear, and color stability of three commercially available resin composites representing distinct material categories: short fiber-reinforced (everX Posterior), zirconium silicate-reinforced nanohybrid (Vittra APS), and shade-adaptive nanohybrid (Harvard MultiChrome).
Materials And Methods:
A total of 240 disc-shaped specimens were prepared (n = 80 per material) and divided into bleached and non-bleached groups. The bleaching protocol consisted of three 20-minute applications of 35% hydrogen peroxide gel in a single session. Surface roughness (Ra, μm), Vickers microhardness (VHN), and wear (μm) were assessed using optical and mechanical testing methods. Color changes (ΔE00) were measured using an intraoral spectrophotometer.
Statistical Analysis:
Independent t-tests and ANOVA with Tukey's HSD post-hoc test were used for statistical analysis (α = 0.05).
Results:
Bleaching significantly increased surface roughness only in Vittra APS (0.245 ± 0.01 to 0.266 ± 0.03 μm, +8.6%, p = 0.015), while everX Posterior (+3.1%, p = 0.09) and Harvard MultiChrome (+2.9%, p = 0.38) remained unchanged. Microhardness significantly decreased in everX Posterior (84.3 ± 1.42 to 78.6 ± 2.32 VHN, -6.8%, p = 0.0001) and Vittra APS (81.2 ± 2.22 to 77.0 ± 5.69 VHN, -5.2%, p = 0.003), whereas Harvard MultiChrome showed no significant change (-3.2%, p = 0.18). Wear significantly increased in Vittra APS (+30.0%, p = 0.02) and Harvard MultiChrome (+25.9%, p = 0.03), while everX Posterior remained unaffected (+3.1%, p = 0.47). All materials exceeded the clinical acceptability threshold for color change (ΔE00 > 1.8): Harvard MultiChrome (3.8 ± 1.4), Vittra APS (10.6 ± 1.0), and everX Posterior (10.9 ± 4.6) (p ≤ 0.05).
Conclusions:
Harvard MultiChrome demonstrated relatively less degradation, while everX Posterior showed superior wear resistance. However, none maintained clinically acceptable color stability after bleaching. Mechanical alterations were modest; color changes were clinically unacceptable for all materials. Shade-adaptive composites remain underrepresented, and findings require cautious interpretation pending further studies.
