Evaluation of bleaching efficacy, microhardness, and trans-amelodentinal diffusion of a novel bleaching agent for an in-office technique containing hexametaphosphate and fluoride

Abstract

Objective: This study evaluated in vitro the effects of calcium gluconate (CaGlu), sodium fluoride (NaF), sodium hexametaphosphate (HMP), and NaF/TMP added to a 35% hydrogen peroxide (H₂O₂) bleaching gel on the color change, enamel hardness, and trans-amelodentinal diffusion.

Materials and methods: Enamel discs/bovine dentin (n = 150) were divided according to the bleaching gel: 35% H₂O₂ (H₂O₂); 35% H₂O₂ + 0.1% NaF (H₂O₂/NaF); 35% H₂O₂ + 1% HMP (H₂O₂/HMP); 35% H₂O₂ + 0.1% NaF + 1% HMP (H₂O₂/NaF/HMP), and 35% H₂O₂ + 2% CaGlu (H₂O₂/Caglu). The bleaching gels were applied three times (40 min/session) at 7-day intervals between each application. Then, color alteration (ΔE), whitening index (ΔWI_D), percentage of surface hardness loss (% SH), cross-sectional hardness (ΔKHN), and trans-amelodentinal diffusion were determined. Data were submitted for analysis of variance (ANOVA), followed by the Student-Newman-Keuls test (p < 0.05).

Results: All bleaching gels showed significant color changes after treatment (p < 0.001). ΔE and ΔWI_D were similar among the evaluated gels. Mineral loss (% SH and ΔKHN) and trans-amelodentinal diffusion of hydrogen peroxide were lower for H₂O₂/NaF/HMP; the H₂O₂/CaGlu group presented the highest values about the other groups (p < 0.001).

Conclusion: It is possible to conclude that the addition of NaF/HMP to the in-office bleaching agent did not interfere with the bleaching efficacy and reduced enamel demineralization and H₂O₂ diffusion.

Clinical significance: The association of NaF/HMP to the bleaching gel can be used as a novel approach for minimizing the adverse effects of H₂O₂ by-products and with similar clinical efficacy.

Keywords: Esthetics; Peroxides; Phosphates; Sodium fluoride; Tooth bleaching agents; Tooth demineralization.