Review of the current status of tooth whitening with the walking bleach technique

 Table 1. Old and new formulae (as cyclic peroxoborate) of sodiumperborate.

The chemical reaction mentioned above emphasizes that release of H2O2 by mixing sodium perborate and water is achieved without supplementary addition of H2O2. Several studies have reported bleaching effectiveness by comparing mixtures of sodium perborate with distilled water or H2O2 in different concentrations. Rotstein et al. (1991d, 1993) and Weiger et al. (1994a) did not report any significant difference in the effectiveness between sodiumperborate mixed with 3-30%H2O2 and the sodiumperborate-distilled water mixture. However, the whitening effect of the second mixture can take longer, so that more frequent changes of the bleaching agent may be necessary. The shade stability of teeth treated by a mixture of perborate and water is as high as the shade stability of teeth in which a mixture of sodium perborate with 3 or 30% H2O2 was used (Rotstein et al. 1993, Ari & Ungor 2002). Other surveys found that mixing sodiumperborate with 30%H2O2wasmore effective than mixing with water (Ho & Goerig1989,Warren et al. 1990). Freccia et al. (1982) showed that the walking bleach technique with a mixture of 30% H2O2 and sodiumperborate was as effective as the thermocatalytic technique. 
Complications of the walking bleach technique are contributed to an acidic pH of the bleaching reagent; 30% H2O2 has a pH value between 2 and 3.When 30% H2O2 is mixed with sodium perborate in a ratio of 2 :1 (g mL_1), the pH of this mixture is alkaline. If further 30% H2O2 is added, it becomes acidic (Kehoe 1987, Rotstein & Friedman 1991). Weiger et al. (1993) tested the pH value of mixtures consisting of 2 g sodiumperborate and 1mL of 10-30% H2O2 or distilled water. Initially, a neutral or weak alkaline pH for all compositions was apparent, e.g. the mixture of 30% H2O2 and perborate showed an initial pH value of 7.0-8.7 depending on the perborate used (mono-, tri- or tetrahydrate). It was also shown that the pH significantly in creased with decreasing concentration of H2O2. The highest initial pH was observed when sodiumperborate was mixed with water. Within a day, a distinct increase of the pH value of 9- 11was achieved. This is true for a sodiumperborate suspension mixed with water or H2O2. This increase in pH is desirable because the whitening effectiveness of buffered alkalineH2O2 is significantly higher than the effect of unbuffered H2O2 (Frysh et al.1995). 
Other H2O2-separating agents such as sodium percarbonate (2Na2CO3_H2O2) can be used to bleach discoloured teeth. Suspensions consisting of sodium percarbonate and water or 30%H2O2 had a good bleaching effect on teeth which were artificially stained in vitro by iron sulphide (Kaneko et al. 2000). However, clinical studies using sodium percarbonate have not been reported. 
Aldecoa & Mayordomo (1992) described good clinical success rates when using a mixture consisting of sodium perborate and10%carbamide peroxide gel. This suspension was used as a temporary intracoronal filling after application of a regular walking bleach paste with sodium perborate and H2O2. The authors claimed that this procedure led to long-term stability of the tooth whitening therapy.