Synthesis, characterization and evaluation of novel bleaching gels containing bioactive glass and nano-hydroxyapatite on hydrogen peroxide diffusion, bleaching efficacy and enamel protection.

objectiveTo evaluate the effect of adding bioactive glass (nBG) and hydroxyapatite (nHAp) nanoparticles to an experimental bleaching gel on 40% hydrogen peroxide (H2O2) diffusion into the pulp chamber, bleaching efficacy (BE), potential of hydrogen (pH) and its effects on enamel’s chemical, mechanical, and physical properties. MATERIALS AND

methodsNanoparticles of nBG and nHAp were synthesized, characterized, and incorporated into a 40% H2O2 bleaching gel. Thirty premolars were divided into three groups (n = 10): (1) Control group = 40% H2O2 bleaching gel; (2) nBG group: 40% H2O2 bleaching gel + bioactive glass (Si: Ca: P); (3) nHAp group: 40% H2O2 bleaching gel + nano-hydroxyapatite. The H2O2 diffusion was measured by UV-Vis spectrophotometry, and BE was assessed by digital spectrophotometry (ΔEab,) before and after 7 days bleaching. The pH was measured at baseline and after 45 min. To evaluate enamel surface alterations, 120 enamel blocks from 30 third molars were analyzed for their chemical (EDS, XRD and Raman), mechanical (microhardness, nanohardness and elastic modulus), and physical (roughness and optical profilometry) properties before bleaching treatment (BT) and after one-week treatment (AT). All data were subjected to statistical analysis (α = 0.05).

resultsThe nBG and nHAp groups showed significantly lower H₂O₂ diffusion than the control group (p = 0.01), with no differences in BE (p < 0.32). The initial pH of the nBG group was significantly different from the others (p = 0.01), but this difference was not maintained at 45 min. The nHAp group presented higher Ca (p = 0.01) and P (p = 0.01) values and a greater hydroxyapatite peak intensity than other groups. A significant time-group interaction was observed for mechanical and physical properties (p = 0.01). While no BT differences were found, the values of these properties significantly increased for the nHAp group at AT.

conclusionIncorporating nBG and nHAp, into a 40% H2O2 bleaching gel significantly reduces H2O2 diffusion into the pulp chamber without compromising BE. Although both materials mitigate deleterious effect of tooth bleaching, nHAp demonstrates a superior performance in preventing demineralization. CLINICAL RELEVANCE: The incorporation of nBG and nHAp into bleaching gels represents a promising approach for a safer in-office bleaching treatment.