Do resin composite type and bleaching regimen influence tooth color change under attachment presence? An in vitro study

Objective 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. Methods 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%). Results 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. Conclusion 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.