Effects of different bleaching methods on the color stability, microhardness, and surface roughness of single-shade composites

BACKGROUND: This in vitro study aimed to evaluate the effects of different bleaching methods on the color stability, microhardness, and surface roughness of single-shade resin composites. METHODS: Four single-shade resin composites (Charisma Diamond One, Vittra APS Unique, Omnichroma, Zenchroma) and one universal-shade resin composite (Essentia Universal) were tested. Two hundred disc-shaped specimens were fabricated and stained in a coffee solution for 12 days After staining, specimens were assigned to four groups: at-home bleaching (10% carbamide peroxide), in-office bleaching (40% hydrogen peroxide), laser-assisted bleaching (Er: YAG), and a non-bleached control. Color (ΔE₀₀), surface roughness (Ra), and Vickers microhardness (VHN) were measured at baseline, after staining, immediately post-bleaching, and at 1-week and 1-month follow-ups. RESULTS: All bleaching protocols significantly affected surface properties and color stability (p < 0.05). Laser-assisted bleaching induced the greatest surface roughness increase and microhardness reduction (p < 0.05), while at-home bleaching had the least effect. Essentia Universal showed the highest resistance, whereas Charisma Diamond One and Omnichroma were more prone to discoloration and mechanical changes. Microhardness partially recovered over time (p < 0.05), but color and roughness changes persisted. CONCLUSIONS: Both bleaching protocol and composite type influence the performance of single-shade resin composites. These results may guide clinicians in material selection and treatment planning. Essentia Universal showed superior resistance to bleaching-related changes, while laser-assisted bleaching, although effective for whitening, compromised mechanical and esthetic properties.