Evaluation of hydrogen peroxide diffusion in the pulp chamber, bleaching efficacy, and physicochemical properties of an experimental in-office bleaching gel containing a hydroxyapatite-capsaicin composite

Abstract

This study assessed the hydrogen peroxide (HP) diffusion into the pulp chamber, bleaching efficacy (BE), surface roughness (Ra), and Knoop microhardness (KHN) of an experimental bleaching gel containing a hydroxyapatite-capsaicin composite (HAp-CAP). Human premolars were randomly assigned to three groups (n = 9) based on the dental bleaching gel used (50 min; one session): only 35% HP, 35% HP + HAp-CAP, and not exposed to bleaching (negative control; NC). HP diffusion (µg/mL) into the pulp chamber was assessed using UV-Vis spectrophotometry, and BE (ΔE_ab, ΔE₀₀, and WI_D) was evaluated using a digital spectrophotometer. Human molars were used to determine Ra and KHN before and 7 days after the bleaching procedure, and for Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) analyses. A paired t-test or t-test was used for statistical analysis (α = 0.05). A higher amount of HP into the pulp chamber and significant BE (ΔE_ab, ΔE₀₀, and WI_D) were observed for 35% HP and 35% HP + HAp-CAP compared to NC (p < 0.001), with no significant difference between them (p > 0.05). SEM and EDS demonstrated material deposition on the enamel surface after bleaching for 35% HP + HAp-CAP, which helped maintain the KHN (p > 0.05). Furthermore, Ra increased for both groups (p < 0.05). The 35% HP + HAp-CAP did not decrease HP diffusion into the pulp chamber, reduced KHN values, and increased Ra. Material deposition on the enamel surface was observed, and BE was effective.

Keywords: Bleaching gels; Dental enamel permeability; Hydrogen peroxide; Tooth bleaching.