Professional Teeth Whitening Explained

The chemistry, briefly

Whitening gels contain hydrogen peroxide or carbamide peroxide, which releases hydrogen peroxide. The peroxide diffuses through enamel into dentine and breaks apart the large pigmented molecules that have accumulated there, into smaller, less visibly coloured ones.

This is different from abrasive whitening toothpastes, which remove surface staining but do not alter the underlying colour of the tooth.

In-office versus supervised home whitening

In-office whitening uses higher concentrations under controlled conditions with the gums isolated, and produces visible change quickly. Dentist-supervised home whitening uses custom-fitted trays and lower concentrations worn over a period of days or weeks.

Both are widely used, and many patients combine them. The custom tray is the important detail in home whitening: it holds gel against the teeth and limits contact with the gums, which is the main difference between supervised whitening and over-the-counter kits.

Sensitivity

Temporary tooth sensitivity is the most common side effect and usually settles within days of finishing. It can often be reduced by shortening wear time, spacing sessions further apart, or using a desensitising gel or high-fluoride paste alongside treatment.

Sensitivity that persists, or gum irritation from ill-fitting trays, is worth reporting rather than pushing through.

What whitening cannot do

Peroxide does not change the colour of dental materials. Crowns, veneers, bonded composite and fillings stay the shade they were made, which means visible restorations may need replacing after whitening to match.

Whitening is also less predictable for grey-toned discolouration, tetracycline staining, and single dark teeth that have had root canal treatment — those cases often need a different approach entirely.

Sensible expectations

Results vary between individuals and are not permanent. Colour gradually returns depending on diet, smoking and habits, and periodic top-up sessions are common. An examination before whitening matters: peroxide applied over untreated decay, a cracked tooth or inflamed gums is a source of avoidable discomfort.