Influence of coating dental enamel with a TiF₄-loaded polymeric primer on the adverse effects caused by a bleaching gel with 35% H₂O₂.

Abstract

To evaluate whether coating enamel with a polymeric primer (PPol) containing titanium tetrafluoride (TiF₄) before applying a bleaching gel with 35% H₂O₂ (35% BG) increases esthetic efficacy, prevents changes in morphology and hardness of enamel, as well as reduces the cytotoxicity from conventional in-office bleaching. Standardized enamel/dentin discs were stained and bleached for 45 min (one session) with 35% BG. Groups 2TiF₄, 6TiF₄, and 10TiF₄ received the gel on the enamel previously coated with PPol containing 2 mg/mL, 6 mg/mL, or 10 mg/mL, respectively. No treatment or application of 35% BG directly on enamel were used as negative control (NC), and positive control (PC), respectively. UV-reflectance spectrophotometry (CIE L*a*b* system, ΔE₀₀, and ΔWI, n = 8) determined the bleaching efficacy of treatments. Enamel microhardness (Knoop, n = 8), morphology, and composition (SEM/EDS, n = 4) were also evaluated. Enamel/dentin discs adapted to artificial pulp chambers (n = 8) were used for trans-amelodentinal cytotoxicity tests. Following the treatments, the extracts (culture medium + bleaching gel components diffused through the discs) were collected and applied to odontoblast-like MDPC-23 cells, which were assessed concerning their viability (alamarBlue, n = 8; Live/Dead, n = 4), oxidative stress (n = 8), and morphology (SEM). The amount of H₂O₂ in the extracts was also determined (leuco crystal violet/peroxidase, n = 8). The numerical data underwent one-criterion variance analysis (one-way ANOVA), followed by Tukey's test, at a 5% significance level. Regarding the ΔE₀₀, no difference was observed among groups 2TiF₄, 6TiF₄, and PC (p > 0.05). The ΔWI was similar between groups 2TiF₄ and PC (p > 0.05). The ΔWI of group 6TiF₄ was superior to PC (p < 0.05), and group 10TiF₄ achieved the highest ΔE₀₀ and ΔWI values (p < 0.05). Besides limiting enamel microstructural changes compared to PC, group 10TiF₄ significantly increased the hardness of this mineralized dental tissue. The highest cellular viability occurred in 10TiF₄ compared to the other bleached groups (p < 0.05). Trans-amelodentinal H₂O₂ diffusion decreased in groups 2TiF₄, 6TiF₄, and 10TiF₄ in comparison with PC (p < 0.05). Coating enamel with a PPol containing TiF₄ before applying a 35% BG may increase enamel microhardness and esthetic efficacy and reduce the trans-amelodentinal cytotoxicity of conventional in-office tooth bleaching. The PPol containing 10 mg/mL of TiF₄ promoted the best outcomes.