Four things people believe about teeth whitening that are not true

Myth one: whitening strips away your enamel

This is the fear we hear most often, and it is understandable. Whitening gel is a bleaching agent, and bleach sounds harsh. In practice, the peroxide used in professionally supervised whitening works by passing through the enamel and breaking down the stain molecules in the tooth beneath. It does not dissolve, thin or roughen enamel when the concentration is appropriate and the trays fit properly. Decades of use and study support this.

What whitening can do is make teeth temporarily sensitive, because the same openness in the enamel that lets the gel in also lets cold reach the nerve more easily. This settles within days of stopping and can be managed with a desensitising toothpaste or by spacing out the applications. The damage people worry about tends to come from somewhere else entirely: acidic DIY remedies, abrasive charcoal powders, or over-the-counter products used far beyond their instructions.

Myth two: it works on every tooth, including crowns and fillings

Whitening gel changes the colour of natural tooth tissue and nothing else. Porcelain crowns, veneers, bridges and white composite fillings are made of materials that do not respond to peroxide. They will stay exactly the shade they were made in while the natural teeth around them become lighter. If you have a crown on a front tooth, it can end up looking darker simply because its neighbours have changed.

That is not a reason to avoid whitening. It is a reason to plan the sequence. Where a front tooth needs a crown, veneer or filling, whitening usually comes first. We wait a fortnight for the new shade to settle, then make the restoration to match it. Teeth that have darkened after root canal treatment are a different case again, and are often better treated with internal whitening placed inside the tooth itself.

Myth three: a kit from the shop or the internet does the same job

In the UK, whitening with a meaningful concentration of hydrogen peroxide is classed as dentistry and may only be prescribed by a registered dentist, with the first application supervised. Products sold freely over the counter are limited to a tiny fraction of that strength, which is why so many of them disappoint. Those sold online from abroad at higher strengths sit outside UK regulation, and the concentration on the label is not always the concentration in the syringe.

The other difference is the tray. A shop-bought kit comes with a one-size strip or a boil-and-bite mouthpiece, which holds the gel unevenly and lets it leak onto the gums. The trays we provide are made to measure from a scan of your teeth, so each tooth receives the same thin film of gel and the gums are protected. Our Enlighten course, two weeks in made-to-measure trays followed by a finishing visit in the surgery, starts from £895, and we examine the teeth before prescribing it, because whitening over an undiagnosed cavity or gum problem is a bad idea.

Myth four: once your teeth are white, they stay white

Whitening is not permanent, and anyone who tells you otherwise is overselling. Teeth pick up stain from the same sources after treatment as before: tea, coffee, red wine, curry, smoking, and simply growing older. Most people find the result holds well for a year or two, then gradually softens. How quickly depends on habits more than on the treatment itself.

The good news is that maintenance is simple. Because you keep your trays, a top-up of a night or two every few months is usually enough to hold the shade, and top-up gel is available from the practice. A hygienist visit before whitening removes surface stain and gives the gel a clean tooth to work on. If you ever lose or damage the trays, a fresh scan and a new set is a quick appointment rather than a return to the beginning.

How we approach it here

Every whitening case at Sardinia House begins with a check of the teeth and gums, an iTero™ scan and a frank conversation about what shade is realistic. Teeth with grey or banded discolouration lighten less predictably than those that are simply yellowed, and we would rather say so beforehand. We also record the starting shade, so that the change can be measured rather than remembered.

The written plan sets out the fee, the number of nights and what to do if sensitivity appears. A hygienist appointment beforehand is usually worthwhile, since surface stain comes off with a polish and the gel then works on the tooth rather than on what is sitting on it. If you are planning bonding, veneers or a crown on a front tooth, tell us at the outset, so that the whitening is sequenced first and the new work is matched to the finished shade rather than the old one.