Influence of Enzymatic Catalysis and Reduced Application Time on Enamel Chemical and Structural Changes Induced by In-Office Bleaching

Objectives: This study evaluated a bleaching strategy combining horseradish peroxidase (HRP) and a polymeric scaffold with 35% hydrogen peroxide, compared with a conventional in-office bleaching protocol. Methods: The study was conducted in two experimental phases. In Phase I, enamel from five sound human premolars was pooled, homogenized, and divided into technical aliquots for ATR-FTIR analysis and quantification of reactive oxygen species (ROS). In Phase II, 24 human premolars were allocated to four experimental groups (n = 6 per group) to evaluate surface microhardness, post-treatment surface roughness, and elemental composition. Four protocols were investigated: NC (negative control), G45 (35% H2O2 for 45 min), G15 (35% H2O2 for 15 min), and G15SP (polymeric scaffold + HRP for 15 min). Results: G15SP exhibited lower post-treatment surface roughness and greater preservation of enamel microhardness compared with the conventional G45 protocol. Exploratory ATR-FTIR analysis showed relatively stable PO43−/CO32− ratios in NC, minor variations in G15SP, and the greatest treatment-associated variations in G45. Descriptive ROS analysis showed the highest initial ROS generation in G15SP. EDS analysis showed a lower Ca/P weight ratio in G45, whereas G15SP maintained values closer to those observed in the untreated control. Conclusions: Enzymatic catalysis combined with a polymeric scaffold was associated with greater preservation of enamel elemental composition, surface characteristics, and mechanical properties compared with the conventional 45-min bleaching protocol. Clinical significance: Modulation of hydrogen peroxide reactivity through enzymatic catalysis and a polymeric scaffold may represent a promising strategy to reduce the structural impact of in-office bleaching while shortening peroxide exposure time. Its clinical bleaching efficacy should be confirmed in studies specifically designed to evaluate color change.