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The question

I whiten my teeth frequently – those strips and that toothpaste do wonders! My dentist says it's hurting my teeth, but the packaging says it's totally harmless. Where do you stand?

The answer

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Tooth discoloration is very common and can be caused by tooth decay, aging, stains from food and drinks such as coffee and tea, smoking and certain medications. As a result, tooth whitening treatments have become increasingly popular and easier to use, and can make a noticeable difference in appearance. In general, they are considered safe when used correctly, but there are some precautions to take when using them.

Whitening will only work on natural teeth, not caps, crowns, veneers or fillings. Products such as whitening toothpastes and gums contain an abrasive material that removes surface stains but do not actually bleach the teeth. Gels, strips and paint-on kits contain a bleaching agent – peroxide – which changes the actual colour by penetrating deeper into the teeth.

The higher the concentration of peroxide, the stronger the whitening power. The formulas used by dentists have higher concentrations and are more expensive but they tend to work better than over-the-counter products, but due to their potency, if left on too long or used too frequently the high level of peroxide can cause damage to the integrity of the teeth.

Regardless of the type of product you use (professional or over-the-counter), the results are not permanent and usually last about three to six months, depending on your general dental hygiene and what you eat and drink. It is not recommended to use a whitener more than once every six months.

Your dentist may be concerned if you are using the product too frequently or leaving it on beyond the time instructed. If you are using the product as directed, however, it should be safe and not hurt your teeth.

In terms of regulation, tooth whitening treatments are reviewed by Health Canada to check that they have proper safety labelling and instructions, but the ultimate safety of the product is the responsibility of the manufacturer. When searching for a good product, look for a seal of approval from the Canadian Dental Association.

Despite all of this, there can be some side effects. Most are mild but can include tooth sensitivity and irritation of the gums. To minimize side effects, read the instructions and follow them carefully, use the product for no longer than 14 days and stop using it if you develop any sensitivity or pain.

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Tooth whitening is not recommended for children under 16 years of age, pregnant women and people with sensitive teeth or gum disease.

Send family doctor Sheila Wijayasinghe your questions at She will answer select questions, which could appear in The Globe and Mail and/or on The Globe and Mail web site. Your name will not be published if your question is chosen.

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The content provided in The Globe and Mail's Ask a Health Expert centre is for information purposes only and is neither intended to be relied upon nor to be a substitute for professional medical advice, diagnosis or treatment.

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