Activator-Enhanced Bleaching of Tooth Discolouration Components by Hydrogen Peroxide

Extrinsic tooth discolouration (ETD) is partially ascribable to melanoidin 'browning products' (MBPs) produced from Maillard reactions. These reactions are triggered by the condensation of acquired pellicle glycoprotein side-chain amino groups with reducing sugars, and chemical models of MBPs can be employed for spectrophotometric monitoring of the activities of tooth-whitening products. Objectives: Here, we have explored the influence of a co-applied amino-alcohol bleaching activator (ABA), a component of an 'in-office' H₂O₂-containing tooth-whitening formulation [1], on the rate of bleaching of a model MBP system by H₂O₂. Methods: MBPs were generated from the reaction of 50.0 mM D-glucose with an equivalent concentration of L-lysine in phosphate buffer (PB, pH 7.00) at 60^oC. Following cooling and appropriate dilution with further PB, a MIRA-100 spectrophotometric auto-analyser was employed to simultaneously monitor the rate of decrease in the MBP absorbance (340 nm) of a series of 60 reaction mixtures at 35^oC. These reaction mixtures contained either 0, 10.0, 20.0, 40.0, 50.0 or 100.0 mM added H₂O₂, and 10 selected ABA:H₂O₂ molar ratios (0.00-2.00) for each H₂O₂ concentration examined. Statistical analysis was conducted by analysis-of-variance (ANOVA) of log_e-transformed absorbance data in this split-plot experimental design. Results: ANOVA of kinetic data acquired revealed highly significant differences in the rate of bleaching of MBPs between (1) added H₂O₂ levels, (2) time-points and (3) ABA:H₂O₂ molar ratios (p < 0.001 in each case); the bleaching rate increased with increasing ABA:H₂O₂ mole ratio. Conclusions: Results acquired demonstrate that ABA accelerates the rate of bleaching of MBPs by H₂O₂. This activity may arise from its ability to (1) promote the generation of bleaching-active ^.OH radical from its H₂O₂ precursor and/or (2) react with MBPs in a manner which facilitates attack of ^.OH and/or H₂O₂ on these targets. [1]: Wyten Chairside Gel, Smilestudio UK, UK.