Hydrogen Peroxide Versus Sodium Hypochlorite: All a Matter of pH?

Hydrogen peroxide (H₂O₂) and sodium hypochlorite (NaOCl) solutions are similar in that they contain oxidizing agents with a bleaching effect. NaOCl solutions are stable at a high pH, at which they also exert increased cleansing/proteolysis. On the other hand, H₂O₂ solutions are natively acidic, yet gain bleaching power on organic stains when alkalized. It was investigated whether alkalizing a H₂O₂ solution would also let it dissolve soft tissue or increase its bleaching power on blood-stained dentin.

The stability of alkalized H₂O₂ solutions was assessed by iodometric titration. Soft tissue dissolution was investigated on porcine palatal mucosa. The bleaching effect (ΔL∗) after 60 minutes of exposure was monitored in blood-stained human dentin using a calibrated spectrophotometer. To compare similar molarities, 2.5% H₂O₂ solutions were used here, and 5.0% NaOCl was used as the positive control, whereas nonbuffered saline solution served as the negative control.

Adding alkali (NaOH) to the H₂O₂ solutions rendered them unstable in a dose-dependent manner. A H₂O₂ solution of pH 11.1 was chosen for the main experiments (tissue dissolution and bleaching effect) and compared with a native counterpart (pH = 4.7). Alkalizing the H₂O₂ solution had no discernible effect on its soft tissue dissolution or bleaching power (P = .75 compared with the native H₂O₂ solution). The NaOCl solution of similar molar concentration had a considerably (P < .001) higher tissue dissolving and bleaching effect under current conditions.

The proteolytic/bleaching effects of NaOCl solutions are unique and cannot be achieved by altering the pH of peroxide solutions.