Effect of a New Formulation Bleaching Gel Containing Nanosized β-Calcium Glycerophosphate on Mechanical Properties, Color, and Cytotoxicity Response: In Vitro Study.

Aim: This study aimed to evaluate, in vitro, the effects of fluoride (F) and nano-sized β-calcium glycerophosphate (β-CaGPnano) added to a 35% H₂O₂ bleaching gel (HP) on the enamel hardness, morphological properties, the color change, trans-amelodentinal diffusion of H₂O₂, and cytotoxicity.

Methods: Bovine enamel/dentin samples (n = 126) were divided according to the bleaching gel: a) 35% Hydrogen Peroxide (HP); b) HP Blue 35%-FGM-Produtos Odontológicos (HP Blue); c) HP + 0.1% NaF (HP/F); d) HP + 0.25%β-CaGPnano (HP/0.25%β-CaGPnano); e) HP + 0.1% NaF + 0.25%β-CaGPnano (HP/F/0.25%β-CaGPnano); f) HP + 0.5%β-CaGPnano (HP/0.5%β-CaGPnano); g) HP + 0.1% NaF + 0.5%β-CaGPnano (HP/F/0.5%β-CaGPnano). The bleaching gels were applied thrice (40 min/session) at 7-day intervals between each application. Zeta potential (Zp), polydispersity index (PdI), percentage of loss of surface Vickers hardness (%VHN), surface roughness (Ra), color change, enamel surface morphology, trans-amelodentinal penetration of H₂O₂, and cell viability (MDPC-23 odontoblast-like cells) were determined.

Results: Similar ZP and PdI values were observed for all bleaching gels (p > 0.05). The treatment with HP/F/0.25%β-CaGPnano resulted in a decrease in %VHN by 86.0%, 81.0%, and 66.0% compared to the HP, HP/F, and HP Blue gels (p < 0.05). For Ra, HP and HP Blue were similar (p > 0.05). All groups receiving F or β-CaGPnano showed a significant increase in color change (p < 0.05). The F/0.5%β-CaGPnano resulted in the lowest H₂O₂ diffusion/oxidative stress (p < 0.05). A significant reduction in cell viability was observed in all bleached groups compared to the NC (p < 0.05). The F and/or β-CaGPnano gels resulted in the highest level of cell viability (p < 0.05).

Conclusion: Within the limitations of the present study, it was concluded that the incorporation of fluoride and nano-sized β-calcium glycerophosphate (F/β-CaGPnano) into the 35% hydrogen peroxide (H₂O₂) bleaching gel significantly enhanced its whitening efficacy. The modified formulation also reduced enamel mineral loss when compared to the conventional gel. In addition, the presence of F/β-CaGPnano promoted better morphological preservation of dental tissues and resulted in smoother enamel surfaces. Furthermore, the F/0.5%β-CaGPnano formulation effectively reduced the trans-amelodentinal diffusion of H₂O₂, leading to the lowest peroxide penetration and oxidative stress levels among the tested groups. Finally, the addition of fluoride and/or β-CaGPnano reduced the cytotoxic effects and increased cell viability, demonstrating improved biocompatibility of the bleaching gel.