Characterization and Effectiveness of Bleaching Hydrogel With Biosilicate

Objectives: The objective of the study was to characterize an experimental bleaching hydrogel containing 35% hydrogen peroxide (HP) and bioactive biosilicate (BS; Na₂O–CaO–SiO₂–P₂O₅) and determine color change, enamel microhardness, and morphology after its application on sound and early-stage erosive enamel lesions.
Methods: The hydrogel characterization was carried out by pH analysis and H₂O₂ decomposition rate (%HP). Enamel specimens (n=10) were immersed in citric acid (5min) and submitted to (35HP_BS) experimental hydrogels containing 35% hydrogen peroxide (HP) incorporated with 0 - 10 w/v %BS; (35HP) commercial 35%HP gel (positive control) or remained untreated (NT - negative control). Color (△E00), whiteness index changes (△WID), and surface hardness recovery (SHR, %) were determined before and after treatments. Morphology (scanning electron microscopy - SEM) and enamel chemical content (energy dispersive X-Ray-EDS) were determined after treatments. Data (%SHR, △E00, △WID) were analyzed by ANOVA, Tukey, and Dunnett (p=0.05) tests. pH, %HP, and SEM/EDS were qualitatively analyzed.
Results: Bleaching hydrogels incorporated with BS exhibited a basic pH (9.0), while 35HP and 0%BS groups presented a pH of ~7.0. After 40 min, the decomposition rate was ~30% for 35HP, ~25% for 0%BS, and 18 to 20% for BS groups. No differences in △E00 and △WID were noted among groups containing 0, 2.5, 5, and 7.5% BS and 35HP, but 10% BS displayed higher △E00 and △WID than 35HP (p< 0.05). NT exhibited significantly lower △E00 and △WID than all HP-groups (p< 0.05). 10% BS displayed a higher %SHR (p= 0.022) than 35HP, and according to EDS analysis, Ca and P were observed on the enamel surface of all groups. 35HP-treated group exhibited enamel surface morphological alterations in comparison to NT.
Conclusions: Biosilicate incorporated into 35% hydrogen peroxide bleaching hydrogel maintained the basic pH, did not influence the bleaching efficacy, and 10%BS displayed remineralizing potential in eroded enamel.