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| pH @ 25° C | 7.0 | 5.3 | 4.9 | 4.7 | 4.6 | 4.5 | 4.5 | 4.5 | 4.6 | 4.9 | 6.2 |
Because H2O2 solutions are generally more stable at low pH, some producers may add mineral acids (e.g., phosphoric or nitric acids) to further lower the pH - either in the production process or afterwards. The water used to prepare commercial solutions of H2O2 is generally of very high quality (i.e., de-ionized, with low acidity), and so does not significantly affect the true pH of the product.
Most commercial solutions of H2O2 contain stabilizers (chelating and sequestering agents) which have been added to minimize decomposition of the product through transport and storage. While some stabilizers are alkaline, most are acidic and exhibit buffering properties which add acidity to the product. The amount and type of stabilizers varies between producers, product grades, and H2O2 concentration. Electronic and Reagent grades are more pure (less stabilizers, less acidity) while Dilution and Cosmetic grades have among the highest levels of stabilizers.
Consequently, it is not possible to state with any certainty the pH of commercial H2O2 solutions. However, it is likely that the apparent pH will be pH 4-5 for the more dilute products (3-10% H2O2) and pH 1-4 for the more concentrated products (35-70% H2O2).
How does SpaWhite bleach effectively and not cause burning or sensitivity? The chemistry in SpaWhite stabilizes the hydrogen peroxide, raises solution pH to between 7.0 and 8.0, and forms an aqueous barrier that effectively diminishes the penetration of hydrogen peroxide into the gingival tissues, while selectively allowing the hydroxyl radicals to penetrate the enamel for rapid tooth whitening. It’s only natural that dentists will want to know how this barrier allows bleaching to take place so effectively without causing tissue burning. Because they are trade secrets, the details of the chemistry involved in this process must necessarily be held confidential.
But, superficially, this is what happens:
SpaWhite uses a two-part mix. The ingredients in each part are isolated from each other during storage, as, once the contents of the two are combined, the solution is activated and active life drops to a matter of hours. In the case of the VHP (Variant Hydrogen Peroxide) In-Office formulation, the contents of the two parts are mixed by the dental practitioner, then the mixture applied by way of a single-barrel, non-invasive syringe. In the Take-Home Whitener the components are mixed dynamically from a dual-barreled syringe fitted with an auto-mix nozzle, in which is embedded a helical implement which effectively combines the contents of the tubes to an approximate 50/50 mix.
In each case, one part of the mix contains a high concentration of H2O2 with a pH ranging between 3.9 and 4.8. The other part contains a number of ingredients, one of which is a formulation that extracts moisture form the gingival to form its own soft-tissue barrier. Other ingredients include an active pH balancer, flavorings, and humectants that replace some of the water that is extracted from the gingival.
Gingival cells are predominantly water, whereas teeth contain very little water. SpaWhite uses a proprietary technology called Extracted Aqueous Barrier (EAB), which creates its own barrier which is chemically repellent to H2O2. With bleaches that do not have EAB, paint-on barriers are used with some success to prevent gingival burning. However, this process adds to both cost and patient discomfort in the time required to apply the barrier. What’s more, imperfect application can still result in burning.
A far more impressive aspect of EAB is its ability to prevent tooth sensitivity. Dentine, the layer of the tooth just under the enamel, is composed of dentinal tubules which form fluid paths between the enamel and the nerves. If H2O2 penetrates the enamel and contacts the dentinal tubules, it follows the fluid path to the nerve and tooth sensitivity occurs. However, since water is always present in these tubules, EAB forms its barrier preventing H2O2 from flowing between the inside of the enamel and the tubules. No paint-on dam or other prophylaxis can do this. So why doesn’t this prevent the teeth from being bleached? Because teeth contain relatively little water, virtually no barrier forms on the teeth, allowing H2O2 to penetrate the tooth structure and form the radicals that bleach the enamel. Essentially, SpaWhite takes advantage of the very condition that causes sensitivity to prevent it. This is the innovation that makes SpaWhite truly different from other H2O2 bleaching formulations.
Certain information in this report was supplied by U.S. Peroxide Corp.
