A Comparative Spectrophotometric Investigation of Selected Professional Tooth-Whitening Products

Melanoidin 'browning products' (MBPs) generated from Maillard reactions are at least partially responsible for extrinsic tooth discolouration. Objectives: Here, we evaluated and compared the tooth-whitening efficacies (TWEs) of a series of professional peroxide-containing tooth-whitening products using model MBPs as spectrophotometric probes. Methods: Model MBPs were prepared in aqueous solution [phosphate buffer, pH 7.00] by reaction of L-lysine with D-glucose for 20 hr. at 60^oC. 1.00 g of each bleaching product [1-3] and a hydrogen peroxide (HP)-free control [containing 2.00% (w/w) Carbopol^R gel] was then added to 3.50 ml aliquots of the above pre-cooled MBP solution and following centrifugation, the supernatant was heated at 35^oC for 60 min. Following dilution (1/10), the absorbance of these reaction mixtures at 325 nm (A₃₂₅) was determined (Unicam UV-2 spectrophotometer). TWEs (decrease in A₃₂₅ per hr. per 1.00% (w/w) of HP present) were then computed. Each determination was conducted in triplicate. Statistical analysis was performed by ANOVA of log₁₀-transformed data. Results: Mean (SD) values for the TWEs of products [1], [2] and [3] were 0.075 (0.0035), 0.068 (0.0041) and 0.118 (0.0051) respectively. Statistical analysis revealed that product [3] was significantly more effective than both products [1] and [2]. Conclusions: These data demonstrate that product [3] bleached MBPs more rapidly than products [1] and [2]. This greater bleaching capacity is ascribable to the presence of an amino-alcohol bleaching accelerant in product [3], which may serve to (a) facilitate the production of bleaching-active ^.OH radical from its HP precursor via its complexation of trace levels of 'catalytic' redox-active metal ions present, or alternatively, (b) primarily react with MBPs (a process promoting the attack of ^.OH and/or HP on these agents). [1] and [2]: Zoom! and Zoom 2 respectively, Discus Dental Inc., USA. [3]: Wyten Chairside Gel, Smilestudio UK, UK.