This study aimed to assess the influence of composite resin type used for attachment fabrication and of bleaching regimen on the colour and whiteness changes of bovine enamel submitted to bleaching.

Standardized crowns received attachments made with Voco AlignerFlow LC (AF), 3M™ Transbond™ Supreme LV, (LV), or were left without attachment (WA). Specimens were treated with at-home (HO), in-office (OF), or without bleaching (WB). Therefore, nine groups were established ( n = 10/group): AF/HO, AF/OF, AF/WB, LV/HO, LV/OF, LV/WB, WA/HO, WA/OF, and WA/WB. Color (ΔE ₀₀ ), whiteness index (ΔWI _D ), and colour coordinates (ΔL*, Δa*, Δb*) changes were evaluated by means of digital spectrophotometry. Data were analysed using generalized linear models followed by Bonferroni tests (α = 5%).

AF/HO and AF/OF showed similar ΔE ₀₀ and ΔWI _D ( P = 1.000), both being higher than AF/WB ( P < 0.05). For the LV resin, only LV/OF differed from LV/WB for ΔE ₀₀ ( P = 0.044) and ΔWI _D ( P = 0.018), whereas LV/HO and LV/OF showed similar ΔWI _D ( P = 0.998). In the absence of attachments, WA/HO and WA/OF exhibited higher ΔE ₀₀ and ΔWI _D than WA/WB (both P < 0.001). Specimens without attachments showed higher ΔE ₀₀ , ΔWI _D , and Δb* than those with AF or LV attachments (all P < 0.05). All bleached groups exceed the perceptibility and acceptability thresholds for both ΔE ₀₀ and ΔWI _D , whereas WA/WB remained below these thresholds.

The presence of attachments reduced bleaching effectiveness and compromised colour uniformity, although bleaching remained effective compared to non-bleached conditions. No differences were observed between at-home and in-office protocols, and the type of attachment resin composite also did not interfere in the outcomes.