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.

Whether in the form of one-hour bleaching sessions at your dentist’s office, or home-use bleaching kits purchased at your local drugstore, teeth whitening solutions abound. Yet only 15 percent of the population has tried the cosmetic procedure, and misinformation on the subject is rife.

The long and the short of it is that teeth whitening works. Virtually everyone who opts for this cosmetic treatment will see moderate to substantial improvement in the brightness and whiteness of their smile. However, teeth whitening is not a permanent solution and requires maintenance or "touch-ups" for a prolonged effect.

Bleaching vs. Whitening

According to the FDA, the term "bleaching" is permitted to be used only when the teeth can be whitened beyond their natural color. This applies strictly to products that contain bleach – typically hydrogen peroxide or carbamide peroxide.

The term "whitening," on the other hand, refers to restoring a tooth’s surface color by removing dirt and debris. So any product that cleans (like a toothpaste) is considered a whitener. Of course, the term whitening sounds better than bleaching, so it is more frequently used – even when describing products that contain bleach.

Why Teeth Whitening? Examining Enamel

Most of us start out with sparkling white teeth, thanks to their porcelain-like enamel surface. Composed of microscopic crystalline rods, tooth enamel is designed to protect the teeth from the effects of chewing, gnashing, trauma and acid attacks caused by sugar. But over the years enamel is worn down, becoming more transparent and permitting the yellow color of dentin – the tooth’s core material – to show through.

During routine chewing, dentin remains intact while millions of micro-cracks occur in the enamel. It is these cracks, as well as the spaces between the crystalline enamel rods, that gradually fill up with stains and debris. As a result, the teeth eventually develop a dull, lackluster appearance.

Teeth whitening removes the stains and debris, leaving the enamel cracks open and exposed. Some of the cracks are quickly re-mineralized by saliva, while others are filled up again with organic debris.

Tooth Discoloration: The Two Types of Tooth Stains

There are two categories of staining as it relates to the teeth: extrinsic staining and intrinsic staining.

Extrinsic stains are those that appear on the surface of the teeth as a result of exposure to dark-colored beverages, foods and tobacco, and routine wear and tear. Superficial extrinsic stains are minor and can be removed with brushing and prophylactic dental cleaning. Stubborn extrinsic stains can be removed with more involved efforts, like teeth bleaching. Persistent extrinsic stains can penetrate into the dentin and become ingrained if they are not dealt with early.

Intrinsic stains are those that form on the interior of teeth. Intrinsic stains result from trauma, aging, exposure to minerals (like tetracycline) during tooth formation and/or excessive ingestion of fluoride. In the past, it was thought that intrinsic stains were too resistant to be corrected by bleaching. Today, cosmetic dentistry experts believe that even deep-set intrinsic stains can be removed with supervised take-home teeth whitening that is maintained over a matter of months or even a year.

Now three trends are converging to make whitening a single discolored tooth increasingly worth while, said John D. West, DDS, MSD, a Tacoma, Washington endodontist today at the American Dental Association’s 148th Annual Session.

New techniques have become available.
Interdisciplinary teams are finding new ways to bring their skills to bear on the problem.
People are living longer, so a bright smile is becoming a more worthwhile investment.
"We’re going to live into our hundreds, and we’re going to be socially and sexually active and we’re going to have our teeth," said Dr. West.

From the standpoint of treatment, single discolored teeth fall into two broad categories: those with living pulp and those with dead pulp.

For the teeth with dead pulp, Dr. West described techniques of internal bleaching with "walking bleach." External bleaching with brushes works well also, he said, but it’s time-consuming. So "who wants to do it?"

After cutting access for internal bleaching, the dentist fills the tooth with bleach. One of the chief problems with this approach, he said is reabsorption which occurs in about 6.9 percent of these teeth.

He attributed this problem to an anatomical characteristic found in about 8 percent of teeth: the enamel doesn’t reach the cementum. "I call this the Bermuda Triangle of endodontics," he said.

As a solution, he recommended creating a barrier inside the crown, which should be molded by carefully measuring the shape of the epithelial attachment.

Afterwards, he advised, dentists should make a careful seal over the bleach. Dr. West recommended leaving the walking bleach in place for about six weeks.

Teeth with living pulps offer different options, he said. One common cause of discoloration in such teeth is calcification. In such teeth there are four possible solutions:

A full crown or veneer
Internal bleaching with endodontics
Internal bleaching without endodontics
External bleaching
Veneers are expensive and last only about 10 years, Dr. West said. Restoration, on the other hand, begins the restorative, periodontal cascade.

Endodontics can prevent further internal deterioration. On the other hand, cutting access for internal bleach may kill the pulp.

External bleaching is time-consuming and won’t address the problems inside the tooth.

All these alternatives must be weighed carefully, Dr. West said.

Single-tooth treatments, he concluded, "may seem like a nickel-and-dime thing," but they can potentially bring great benefits to the patient