Effect of 32% Hydrogen Peroxide Bleaching on Surface Properties and Staining Susceptibility of CAD/CAM Hybrid and Feldspathic Ceramics Under Simultaneous Thermocycling–Staining Challenge

Resistance to post-bleaching staining and preservation of surface properties are critical to long-term durability of restorations. This study evaluated the effect of 32% hydrogen peroxide (H₂O₂) in-office bleaching gel on surface roughness (Ra), microhardness, and staining susceptibility of three hybrid computer-aided design/computer-aided manufacturing (CAD/CAM) materials compared with a feldspathic ceramic, subjected to a combined thermocycling-staining protocol.Slice specimens (<i>n</i> = 14/material) were prepared from hybrid ceramic materials: Vita Enamic (VE); Lava Ultimate (LU); Shofu Block HC (SB); and from a feldspathic ceramic material, VitaBlocs Mark II (VB), which served as the control. Seven slices per material underwent CIEDE2000 color difference analysis (ΔE₀₀) after simultaneous staining and thermocycling (1,000 cycles, 5-55°C), with or without a prior bleaching procedure using 32% H₂O₂ gel for three 15-minute cycles. The remaining slices were evaluated for surface roughness (Ra) and Vickers microhardness (VH) before and after bleaching with 32% H₂O₂.Data were analyzed using two-way ANOVA and the Tukey test (α = 0.05).The results showed that bleaching produced no significant changes in ΔE₀₀, Ra, or Vickers hardness number (VHN) for VE, LU, or SB (<i>P</i> > 0.05). VB alone showed a significant reduction in hardness (454 → 323 HV; <i>p</i> < 0.001). Post-staining ΔE₀₀ values remained below the 1.8 clinical acceptability threshold for LU and SB but slightly exceeded it for the non-bleached VE group (≤2.2) and were high for VB (>8). Regardless of bleaching, VB exhibited the greatest color change, whereas SB had the lowest hardness. Ra values for SB and VB were above the critical threshold for bacterial adhesion (0.02 µm).Although a single session of 32% H₂O₂ in-office bleaching significantly decreases the hardness of unglazed feldspathic ceramic, it does not compromise the surface integrity or color stability of hybrid CAD/CAM materials. Therefore, the tested hybrid materials can be safely subjected to 32% H₂O₂-based in-office bleaching without requiring surface pretreatment or postoperative replacement due to material degradation. However, restorative materials should be selected based on a comprehensive assessment of esthetic and mechanical performance to ensure long-term clinical success.