Comparative evaluation of different bleaching agents on the color stability, hardness and surface roughness of...

To evaluate the effect of various bleaching agents of on color, surface roughness and microhardness of indirect restorative materials with different manufacturing methods.

A total of 150 disc-shaped specimens (Ø=8 mm, h = 1.5 mm) were fabricated from 3D-printed resin (Saremco print-CROWNTEC, SAREMCO Dental, Switzerland), milled resin (Lava Ultimate; 3 M ESPE, USA), and conventional resin (Enamel Plus HRi; Micerium, Italy) following the manufacturers' instructions (N = 50/group). Color measurements were performed using a spectrophotometer (VITA Easyshade-V; VITA Zahnfabrik, Germany) under standardized lighting conditions. Microhardness was measured using a Micro Vickers Hardness Tester (HMV-G, Shimadzu, Japan) at a load of 300-gf for 15 s. Surface roughness was measured with a contact profilometer (Perthometer M1, Mahr, Germany). After initial color, microhardness, and surface roughness measurements each group was divided into 5 subgroups: control group, 16% carbamide peroxide (Whiteness Perfect), 35% hydrogen peroxide (Whiteness HP Blue), 16% carbamide peroxide (Opalescence PF), and 40% hydrogen peroxide (Opalescence Boost). After bleaching procedure final color, microhardness and surface roughness of specimens were measured. Color change values were analyzed using Kruskal-Wallis tests followed by Mann-Whitney U tests, while microhardness and surface roughness values were analyzed using two-way ANOVA with Tukey-HSD post-hoc tests (p < 0.05).

Significant differences in ΔE₀₀ values were observed among restorative materials within each bleaching agent group, and among bleaching agents within each restorative material group (p < 0.05). For all bleaching agents, conventional resin group showed the highest color change (p < 0.05), and values exceeded the clinical acceptability threshold when treated with Opalescence PF agent. The type of indirect restorative materials had a significant impact on microhardness, while bleaching agents did not (p > 0.05). The milled-resin group showed the highest Vickers hardness, whereas the printed resin group showed the lowest (p < 0.05). Surface roughness was significantly affected by material type and bleaching agent (p < 0.05). Significantly higher surface roughness was observed in the conventional resin group exposed to Whiteness HP Blue agent (p < 0.05).

The type of indirect restorative material and bleaching agent had an impact on color and surface roughness, while bleaching agents did not influence microhardness. This highlights the importance of material selection in clinical practice.