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.

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.