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

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 (H ₂ O ₂ ) 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% H ₂ O ₂ (H ₂ O ₂ ); 35% H ₂ O ₂  + 0.1% NaF (H ₂ O ₂ /NaF); 35% H ₂ O ₂  + 1% HMP (H ₂ O ₂ /HMP); 35% H ₂ O ₂  + 0.1% NaF + 1% HMP (H ₂ O ₂ /NaF/HMP), and 35% H ₂ O ₂  + 2% CaGlu (H ₂ O ₂ /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 H ₂ O ₂ /NaF/HMP; the H ₂ O ₂ /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 H ₂ O ₂ 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 H ₂ O ₂ by-products and with similar clinical efficacy.
(© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)