Effect of pH conditioners on tooth bleaching

The purpose of this study was to evaluate the effect of pH conditioners on tooth bleaching using hematoporphirin-stained paper and artificially discolored bovine tooth model. Experimental bleaching gels containing 23% hydrogen peroxide, adjusting pH 7.0 by different pH conditioners (NaOH, NaHCO₃, Na₂CO₃, KOH, KHCO₃, and K₂CO₃), were prepared. Each bleaching gel was applied on a hematoporphirin-stained paper, and the light was exposed for 5 min. Before and after bleaching, color was measured and color difference was calculated. Artificially discolored bovine tooth samples were prepared and bleached by four experimental bleaching gels containing NaOH, NaHCO₃, Na₂CO₃, or KHCO₃. The bleaching time was 10 min with light exposure, and bleaching was repeated 10 times. The color of bleached surface was measured at each bleaching period, and color difference was calculated. In the experiment using hematoporphirin-stained paper, degrees of color difference were KHCO₃ > NaHCO₃ > KOH > NaOH > Na₂CO₃ ≥ K₂CO₃. In the experiment using bovine teeth, degrees of color difference were KHCO₃ > NaHCO₃ > NaOH > Na₂CO₃. It was concluded that the bleaching materials with same pH and different pH conditioners showed different bleaching effects and that both cation and anion in the pH conditioners affected bleaching effect.