The effect of bleaching methods on the surface roughness of different restorative materials

Aim: The aim of this study was to evaluate the effects of different bleaching agents on the surface roughness of three different restorative materials fabricated using various manufacturing methods. Material and Method: In this study, a total of 99 samples (8×8×2 mm) were prepared using a nanohybrid composite resin (Neo Spectra™ ST, NS), a subtractive-manufactured nanoceramic hybrid CAD/CAM block (Cerasmart™ 270, CS), and an additive-manufactured permanent resin (Saremco print Crowntec, CT). Each material was divided into two treatment subgroups: in-office bleaching (Opalescence Boost – 40% hydrogen peroxide, 3×20 min) and at-home bleaching (Opalescence PF – 16% carbamide peroxide, 6 hours, 14 days). The bleaching procedures were performed according to the manufacturer's instructions and specified application times. A total of 9 samples (3 baseline, 6 after bleaching) were examined under SEM to evaluate surface morphology. The surface roughness (Ra) and roughness depth (Rz) of the remaining 90 samples (n=15 per group) were measured using a contact profilometer before (T₀) and after bleaching (T₁). Measurements were repeated three times for each specimen, and the average values were recorded. Changes in surface roughness (ΔRa, ΔRz) were calculated by subtracting the T₀ values from the T₁ values. Data were analyzed using Two-way ANOVA, One-way ANOVA, and Paired-samples T test in SPSS software (α=0.05). Results: The interaction between material and bleaching type was statistically significant for both Ra and Rz values after bleaching (p<0.05). In all materials, Ra and Rz values increased significantly after bleaching compared to baseline (p<0.05). Following bleaching, the Ra value of the CT group (p=0.019) and the Rz value of the NS group (p=0.032) were significantly higher in the in-office bleaching group compared to the at-home bleaching group. Differences among the materials in terms of ΔRa and ΔRz were not statistically significant (p>0.05). Conclusions: It was concluded that the tested bleaching agents significantly increased the surface roughness and roughness depth of all three restorative materials, with the in-office bleaching showing a more pronounced effect.