Bleaching of Components Responsible for Tooth Discoloration by Ozone

Objectives: Brown-coloured melanoidins, products derived from the reaction of reducing sugars or carbonyl compounds with amino functional groups of proteins (Maillard reactions) are, at least in part, responsible for extrinsic tooth discolouration (ETD). Indeed, glycoproteins of the acquired pellicle act as substrates for these processes. In this investigation, we probed the ability of therapeutically-relevant doses of ozone (O3) to bleach model brown-pigmented melanoidins. Methods: Melanoidins were generated via the reaction of L-lysine (1.25-250.0 x 10-3 mol. dm-3) with an equivalent concentration of alpha-D-glucose in phosphate buffer (pH 7.00) at 80oC for a period of 240 hr. After cooling, the brown-coloured reaction mixtures were selectively diluted with further phosphate buffer. Aliquots (15.0 ml) of each of these solutions were divided into five equivalent portions (3.00 ml); the first four portions were treated with 1.00, 4.00, 7.00, 10.00 and 13.00 ml of ozonated water (5 ppm) [produced by the TherOzone unit model 2007 (USA)] and 12.00, 9.00, 6.00, 3.00 and 0.00 ml of untreated water respectively (i.e., final volume 16.00 ml); the fifth sample diluted to a total volume of 16.00 ml with untreated water served as a control. Bleaching of these melanoidin solutions by O3 was monitored spectrophotometrically throughout the 280-500 nm wavelength range (each sample treatment was conducted in triplicate). Results: The results demonstrated a significant level of bleaching of melanoidins following treatment with O3. The extent of the bleaching process observed increased with increasing volume of added ozonated water. Conclusions: Ozonated water exerts bleaching actions towards melanoidins which serve as chemical models for components responsible for ETD. The mechanism of this process may involve the ozonation of (>C=C<) bond systems which contribute to the chromophoric properties of such products.