Effects of dental bleaching protocols with violet radiation on the color and chemical composition of stained bovine enamel

•The type of organic pigment in dental structure influences the efficacy of in-office bleaching with violet radiation.•Violet radiation increases the bleaching effectiveness of the high-concentrated carbamide peroxide.•The bleaching protocols did not influence the enamel mineral content. To evaluate the bleaching efficacy of a violet radiation (VR) combined or not with bleaching gels on the color and mineral content of stained teeth. Enamel/dentin blocks were obtained and stained (n = 50) with coffee, red wine, tobacco smoke, or were left non-stained. The stained or not-stained blocks (n = 10) were distributed into five bleaching groups (n = 10): VR, CP (37 % carbamide peroxide), VR/CP, HP (35 % hydrogen peroxide), and VR/HP. Color (ΔE00, ΔL, Δa, and Δb) and whiteness index (ΔWID) changes were evaluated after staining and after bleaching using a spectrophotometer. Calcium (Ca), phosphorous (P), and Ca/P contents (in wt%) were measured after bleaching using energy-dispersive X-ray spectroscopy (EDS). Data was statistically analyzed (α = 0.05) using two-way ANOVA and Tukey tests (ΔE00, ΔWID, ΔL, Δb, wt%) or Kruskal-Wallis and Dunn tests (Δa). VR alone caused higher colorimetric changes on coffee, tobacco and red wine-stained groups compared to non-stained enamel (p < 0.05). VR/CP exhibited higher colorimetric changes compared to CP in coffee and non-stained groups. The VR/CP, HP and VR/HP groups exhibited no change differences (p > 0.05). No differences were observed for the wt% of Ca, P and Ca/P between the groups. The violet radiation was more effective in bleaching stained rather than non-stained teeth. VR combined with 37 % carbamide peroxide was as effective as the HP agent. Besides, no adverse effects could be observed in the enamel mineral content, regardless of the bleaching protocol tested, according to the EDS semi-quantitative analysis.