Comparative effects of integrated and post-applied nano-hydroxyapatite on enamel properties following high-concentration hydrogen peroxide bleaching.

Purpose

This study investigated whether nano-hydroxyapatite (nHAp) can reduce the adverse effects of high-concentration hydrogen peroxide (HP) bleaching - such as mineral loss and surface softening - while maintaining whitening efficacy. Incorporation of nHAp into the bleaching gel was also compared with its application after bleaching.

Methods

Sixty bovine enamel specimens were randomly assigned to six groups and treated with different HP-based protocols with or without nHAp. Color change (ΔE) was measured using spectrophotometry, microhardness with the Vickers test, and surface morphology and elemental composition using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS).

Results

All HP-treated groups showed significant color improvement (ΔE > 3.3, P < 0.05). Post-bleaching nHAp application produced higher ΔE values than bleaching alone, though not to a significant degree. The highest ΔE was observed in the group receiving HP followed by nHAp. Post-bleaching nHAp significantly improved microhardness and calcium content in the Opalescence group, while effects in the BioWhiten group were limited and not significant. SEM analysis revealed superficial granular deposits and partial surface coverage in nHAp-treated specimens, particularly after post-bleaching application.

Conclusion

Incorporation of nHAp during or after HP bleaching can reduce enamel alterations while preserving whitening efficacy, particularly when applied after bleaching in systems lacking intrinsic remineralizing components.