Assessment of bleaching procedures on the optical properties, surface roughness and microhardness of single-shade...

To evaluate the effects of bleaching on the optical properties, surface roughness, and microhardness of various single-shade resin composites.

A total of 210 disc-shaped specimens (6 mm × 2 mm) were fabricated using seven single-shade resin composites (Clearfil Majesty ES-2 Universal, Essentia Universal, Vittra Unique, Charisma Topaz One, OneShade, Omnichroma, and Zenchroma) (n = 30 / group). After 24 h of storage in distilled water at 37 (±) 1 °C, all specimens were immersed in a coffee solution for 144 h. Color change (ΔE₀₀), whiteness index (ΔWI_D), translucency parameter (TP), and gloss (GU) were measured using a spectrophotometer and a glossmeter. Surface roughness (Ra) and Vickers microhardness (VHN) were evaluated at baseline (T0), following staining (T1), and following bleaching (T2) using Opalescence Boost (HP) or Opalescence Quick (CP). Data were analyzed using the Shapiro-Wilk test for normality, followed by Robust ANOVA and Bonferroni post-hoc tests (α = 0.05).

All restorative materials exhibited color changes exceeding both the perceptibility (PT > 0.8) and the acceptability (AT > 1.8) thresholds. The highest discoloration was observed in the VU*CP subgroup (9.05 ± 1.05), while the lowest was observed in the ZC*HP subgroup (1.85 ± 0.43). Both mean Ra and VHN values differed significantly among the restorative materials, regardless of bleaching agent and time-period (p < 0.001).

All tested single-shade resin composites exhibited perceptible and clinically unacceptable color changes. The HP bleaching agent demonstrated the greatest negative effects on surface roughness and microhardness, while among the single-shade resin composites, CME and EU showed the highest degree of susceptibility to these effects. The interactions between restorative materials and bleaching agents should be taken into account when planning the bleaching of restored teeth.