Influence of bleaching gels formulated with nano-sized sodium trimetaphosphate and fluoride on the physicochemical, mechanical, and morphological properties of dental enamel

Abstract

Objectives: To evaluate in vitro the effects of sodium fluoride (F) and nano-sized sodium trimetaphosphate (TMPnano) added to a 35% hydrogen peroxide (H₂O₂) bleaching gel on the color alteration, enamel mechanical and morphological properties, and H₂O₂ transamelodentinal diffusion.

Materials and methods: Bovine enamel/dentin discs (n = 180) were divided according to the bleaching gel: 35% H₂O₂ (HP); 35% H₂O₂ + 0.1% F (HP/F); 35% H₂O₂ + 1% TMPnano (HP/TMPnano); 35% H₂O₂ + 0.1% F + 1% TMPnano (HP/F/TMPnano) and 35% H₂O₂ + 2% calcium gluconate (HP/Ca). The gels were applied 3 times by 40 min; once each 7-day. The Commission Internationale de l'Eclairage (CIE) L*a*b* total color alteration (ΔE), color alteration by CIEDE2000 (ΔE₀₀), whitening index (ΔWI_D), surface (SH) and cross-sectional hardness (ΔKHN), surface roughness (Ra), and transamelodentinal diffusion were determined. Enamel surfaces were evaluated by Scanning Electron Microscopy (SEM) and X-ray Dispersive Energy (EDX). Data were submitted to ANOVA, followed by the Student-Newman-Keuls test (p <0.05).

Results: ΔE, ΔE₀₀, and ΔWID were similar among the gels that promoted a bleaching effect after treatment (p <0.001). Mineral loss (SH and ΔKHN), Ra, and H₂O₂ diffusion were lower for HP/F/TMPnano; the HP and HP/Ca groups presented the highest values (p <0.001). For SEM/EDX, surface changes were observed in all bleached groups, but less intense with TMPnano.

Conclusions: Gels containing F/TMPnano do not interfere with the bleaching effect and reduce enamel demineralization, roughness, H₂O₂ diffusion, and morphological changes.

Clinical relevance: Whitening gels containing F/TMPnano can be used as a new strategy to increase safety and maintain clinical performance.

Keywords: Esthetics; Hydrogen peroxide; Nanoparticles; Phosphates; Sodium fluoride; Tooth bleaching agents.