Teeth Whitening

How whitening actually works

Professional whitening uses hydrogen peroxide or carbamide peroxide, which breaks down and releases oxygen that passes into the enamel and dentine and breaks apart the pigment molecules causing the discolouration.

It changes the colour of natural tooth structure. It does not remove anything from the tooth and it does not thin the enamel when used at appropriate concentrations under supervision.

What it can and cannot change

Whitening responds well to staining from age, coffee, tea, red wine, tobacco and general dietary pigment — the discolouration most people are actually describing.

It responds less predictably, or not at all, to:

• Tetracycline staining — grey or banded discolouration from antibiotics taken during tooth development. It may lighten, but often needs veneers to be resolved.
• Fluorosis — white or brown mottling. The contrast can sometimes become more noticeable before it becomes less so.
• A single dark tooth — usually a tooth that has had root canal treatment, which needs internal whitening rather than external.
• Existing restorations — see below.

Crowns, veneers and fillings do not whiten

This is the single most important thing to understand before starting. Whitening has no effect on ceramic, composite or any other restorative material. If you have crowns, veneers or visible white fillings on your front teeth, whitening the natural teeth around them will change how well they match.

Where restorations are present, the sequence matters: whiten first, allow the shade to stabilise for about two weeks, then replace the restorations to match the new shade. Doing it the other way round means paying for restorations twice.

In-practice and take-home whitening

Both work. They differ in concentration, supervision and time.

In-practice whitening uses a higher concentration applied in a controlled appointment with the gums isolated. It produces a visible change quickly, which suits a deadline, and sensitivity tends to be more concentrated in the first day or two.

Take-home whitening uses custom trays made from scans of your teeth and a lower concentration worn over a period of days or weeks. It is more gradual, generally more comfortable, easier to top up later, and tends to be the option we recommend where there is no time pressure.

The two are often combined: an in-practice session to establish the change, then trays to refine and maintain it.

Sensitivity

Temporary sensitivity is the most common side effect and is expected rather than a sign that something has gone wrong. It usually presents as short, sharp sensations to cold and settles within one to three days of finishing.

It is managed by using a desensitising toothpaste for a week or two beforehand, spacing sessions further apart, reducing the wear time rather than abandoning the treatment, and avoiding very cold food and drink during the course. Pre-existing sensitivity, exposed root surfaces, cracks or untreated decay should be assessed and dealt with first — whitening over untreated decay is not appropriate.

Why supervision matters

An assessment first establishes the cause of the discolouration, which determines whether whitening is the right treatment at all. It also confirms that the gums and teeth are healthy enough, and produces trays that fit, so the gel stays on the teeth rather than on the gum tissue.

Whitening is a dental procedure. Over-the-counter kits with ill-fitting trays and shop-bought “whitening” treatments from non-dental providers are where gum burns and uneven results come from.

How long it lasts

Typically one to three years, depending on diet and habits. Smoking, coffee, tea and red wine shorten it. It is not permanent, and it is not meant to be — which is why custom trays are useful: a single night of top-up gel once or twice a year maintains the result far more cheaply than repeating the full course.

If whitening is not the answer

Where the discolouration will not respond, or where shape and alignment are also part of the concern, the conversation moves to porcelain veneers or composite bonding. Where the teeth are simply covered in surface staining and plaque, a professional clean sometimes achieves more than patients expect, and costs considerably less.