Bleaching efficacy and reduction of cytotoxicity of 6% H₂O₂ in-office bleaching gels formulated with hyaluronic acid, NF_TiO₂ nanoparticles, and violet LED irradiation: in vitro study

The objective is to evaluate the bleaching efficacy and cytotoxicity of innovative low-concentration in-office gels containing 6% hydrogen peroxide (H₂O₂), hyaluronic acid (HA), or carbomer 940 (CAR) as thickeners, titanium dioxide nanoparticles co-doped with nitrogen and fluorine (NF_TiO₂) and irradiated with violet LED. Bovine enamel/dentin disks adapted to artificial pulp chambers were randomly assigned to seven groups (n = 8): NC (negative control), HP35 (commercial control), HA, HA-HP6 + LED, HA-HP6-NP + LED, CAR-HP6 + LED, and CAR-HP6-NP + LED. The bleaching protocol consisted of three 30-min sessions conducted at 7-day intervals, each session involving 20 violet LED cycles (1-min activation / 30-s pause). Bleaching efficacy was assessed by measuring color change (ΔE₀₀) and whiteness index (ΔWI_D). Additionally, hydrogen peroxide diffusion, cell viability, oxidative stress, and cell morphology were evaluated. One-way ANOVA was used for statistical analysis, followed by Games-Howell post-hoc test (ΔE₀₀ and ΔWI_D) and Tukey's test (cytotoxicity) (α = 0.05). Experimental gels showed ΔE₀₀ and ΔWI_D values comparable to those of HP35, with no significant differences observed. The incorporation of NF_TiO₂ (HA-HP6-NP + LED and CAR-HP6-NP + LED) significantly reduced H₂O₂ diffusion and oxidative stress while increasing cell viability (p < 0.05); therefore, preserving cell morphology. The HA-containing group exhibited greater cell proliferation. HP35 demonstrated higher cytotoxicity and cell deformations. Experimental gels containing NF_TiO₂ and 6% H₂O₂, formulated with either HA or CAR as thickeners, exhibited bleaching efficacy comparable to HP35, along with a significant reduction in H₂O₂ diffusion and oxidative stress. The incorporation of nanoparticles significantly enhanced cell viability. The experimental gels may reduce pulpal cytotoxicity and H₂O₂ diffusion, potentially lowering pulp damage and tooth sensitivity. Further studies are required to assess their effects on enamel integrity.