Effect of different home-bleaching techniques for a regular or an extended time on enamel properties

Abstract

Context: The side effects of bleaching products are still incompletely known.

Aims: This work aims to evaluate the effects of bleaching regimens on colour variation, microstructure, roughness, composition and nanohardness of human dental enamel until 8 weeks.

Settings and design: : Twenty teeth were cross-sectioned to obtain eighty enamel fragments (50 × 50 mm) divided into four groups: CN (control Negative-artificial saliva), CP10 (10% carbamide peroxide), HP10 (10% hydrogen peroxide), and WS (whitening strips-10% hydrogen peroxide).

Methods and material: Roughness (atomic force microscopy-AFM and 3-D surface scanning), morphology (confocal laser scanning microscopy-CLSM and AFM), hardness and elastic modulus (nanoindentation), and composition (Raman microspectroscopy) were analysed before the therapy and after 4 and 8 weeks. Colour measures were performed weekly.

Statistical analysis used: : Two-way ANOVA with repeated measures (P < 0.05).

Results: Bleaching stabilizes after 3 weeks for HP10 and after 4 weeks for CP10 and WS. Roughness evaluation showed statistical difference for HP10 after 8 weeks for Sa and Sq, for HP10 and WS after 4 weeks and for CP10 after 8 weeks. The same occurred for hardness and elastic modulus. The morphological evaluation demonstrated the most significant effects after 8 weeks of treatment for HP10 and WS. Composition analysis revealed modifications in peaks related to the organic content spectra (protein) with an increase in detection after 4 weeks, followed by a decrease after 8 weeks.

Conclusions: H₂O₂-based products caused morphological and compositional alterations on enamel.

Keywords: Atomic force microscopy; Raman spectroscopy; dental bleaching; human enamel; hydrogen peroxide.