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Teeth Whitening

Brighter, lighter, whiter...

By Dr. Bill Dorfman

This article is endorsed by the
American Academy of Cosmetic Dentistry.


For the Technical

Hydrogen peroxide is a colorless liquid with a bitter taste and is highly soluble in water and gives an acid solution. Hydrogen peroxide is unstable giving rise to reactive oxygen and acts as a strong oxidizing agent which attacks the organic molecules responsible for tooth discoloration. The bleaching process continues until all of the original pigment is rendered colorless. The chemistry of carbamide peroxide, used for whitening by external bleaching, is slightly different from hydrogen peroxide as it also contains urea, which permits the peroxide to remain in contact with the teeth for longer.

A detailed study into the makeup of a tooth's structure will reveal that its enamel covering is over 95% highly mineralized enamel. At a microscopic level interspersed between the crystals of enamel is a framework (a matrix) that is composed of organic matter. It is assumed that the cause of a tooth's staining is related to the presence of various organic compounds in this matrix which is susceptible to bleaching, without materially affecting the mineral structure.

Risking sensitivity? Higher concentrations of peroxide provide a more rapid bleaching effect; however they may increase the risk of tooth sensitivity, a good reason for a dental professional to carry out the procedure in-office. In addition to concentration, the degree of whitening is also related to the amount of time that the bleaching agent is in contact with the tooth surface; the longer the time, the greater the lightening effect and the greater the likelihood of sensitivity. Tooth sensitivity, generally to hot and cold, normally persists for no more than four days after the cessation of bleaching.

Prevention of sensitivity: Recently the effect of the addition of amorphous calcium phosphate (ACP) to a 16% carbamide peroxide gel has been reported to significantly reduce sensitivity. Another approach to reducing sensitivity is by the addition of desensitizing agents such as potassium nitrate or fluoride, in the form of stannous fluoride, to produce “sensitive-formula” gels. However it can take some time to see results with these two agents.

Home Whitening Systems

“Take home” whitening is the more commonly used technique because it is easy to perform and is less expensive. It generally involves the use of a 6-16% solution of carbamide peroxide in a gel form (approximately equal to 3.4-7% hydrogen peroxide) delivered to the tooth surface by a custom made, vacuum formed, plastic bleaching tray which can be made in your dentists office.

Manufacturers have offered carbamide peroxide in a variety of different concentrations, ranging from 10% to over 20%, but the best combination of safety, limited side effects and speed of action is obtained with a 10% solution of carbamide peroxide approved by the ADA (American Dental Association).

It is generally agreed that most teeth are susceptible to bleaching. The process of home bleaching requires longer contact time compared to power bleaching, but it is safe and the results are generally excellent. General recommendations are for 30 minute applications twice a day. The first subjective change in tooth color is generally observed after two to four sessions of bleaching. In a clinical study of custom tray vital bleaching with 10% carbamide peroxide, 92% of subjects experienced some lightening of teeth after a six-week period. Another clinical trial examined the amount of change in shades of lightness using 10% carbamide peroxide nightly for two weeks and reported that lightness increased by, on average, eight shade units. The dentists or manufacturers guidelines should be followed exactly and not exceeded to avoid damage to the teeth and oral (skin) membranes.

Whitening strips are easier to use than some other products. They generally contain 10% carbamide peroxide gel or less. They come in the form of strips and look like clear band aids that are applied to the tooth surfaces. They should be worn twice a day for 30 minutes each time, for seven days. On average, they claim to lighten more than three shades. Results claim to last about 12 months. Whitening strips containing 6% carbamide peroxide gels take about two weeks to work at 30 minutes per day.

“Paint on” or “Brush on” whitening formulas are also available. These consist of gels that are painted onto the teeth before bed for two weeks. Some claim that this can whiten teeth two to five shades. However these gels can increase salivation and may make your mouth feel goopy, but are relatively inexpensive.

If you are willing to pay more for convenience, some systems consist of individual tubes of 6% gel that each come with a small brush. The gel is squeezed onto the brush and then scrubbed onto the teeth. It does not have to be removed.

When it comes to over-the-counter whitening products, teeth-whitening strips and paint-on whiteners are preferred to over-the-counter “mouth-tray” whiteners, however best results are always attained through a qualified dentist. Since the mouth trays are one-size-fits-all, they can be ill fitting. The trays are filled with gel and worn 45 minutes a day for one week. On average, teeth become two shades whiter. Some find the trays to be messy or uncomfortable. Many tray systems are available.

Whitening Gum is another novelty to hit the market. It doesn't contain peroxide, but it does have a “patented technology” that supposedly breaks up surface stains. To see an effect, you need to chew two pieces for at least 20 minutes, four times a day — not a problem if you are a habitual gum chewer, otherwise it could become a bit tiring.