A common worry is that whitening gel lifts colour by stripping off a thin layer of enamel. It does not. Peroxide gel used as directed lightens the tooth from within and leaves its surface and thickness in place, and the research over more than three decades has not shown meaningful enamel loss from standard whitening.
Enamel can still be harmed by things marketed for whiter teeth, though, and those are worth knowing about.
Whitening works through the enamel, not on it
Most of a tooth's colour comes from dentine, the yellowish layer that sits under the fairly translucent enamel. Over the years, pigments from coffee, tea, wine, tobacco and ageing collect in both layers.
Whitening gels contain hydrogen peroxide, or carbamide peroxide, which releases hydrogen peroxide as it breaks down. The molecule is small enough to diffuse through enamel and into the dentine, where it oxidises the large coloured molecules into smaller, paler ones. A literature review by Joiner (Journal of Dentistry, 2006) described this diffusion and oxidation, particularly within the dentine, as the way peroxide whitening works. Nothing is polished or dissolved away.
Teeth also lose a little moisture during treatment, which is part of why they look brightest straight after a session and settle slightly over the next few days. The difference between the two types of gel is covered in our article on carbamide peroxide and hydrogen peroxide.
Studies that found softer enamel mostly left out saliva
If you read about whitening research, you may come across studies reporting that enamel became slightly softer. Two reviews help put that in context.
Joiner (Journal of Dentistry, 2007) looked at the research on peroxide and the properties of enamel and dentine. Most studies found no significant harmful effect on surface structure, chemistry or hardness. Those that did often used lab methods that did not reflect conditions in the mouth, or solutions acidic enough for erosion to explain the change.
Attin and colleagues (Dental Materials, 2009) then examined 55 studies that measured enamel hardness. Softening was reported more often when samples were stored in artificial rather than human saliva between treatments, and when no fluoride was used. Studies that came closer to real conditions showed less risk of softening, though the authors called for more research done in the mouth. Saliva and fluoride toothpaste both help enamel restore its surface minerals.
Sore teeth after whitening are not a sign of erosion
Sensitivity is a well-known side effect of whitening. It happens because peroxide reaches the dentine and briefly irritates the pulp, the nerve tissue inside the tooth. In a six-week trial of tray whitening, Haywood and colleagues (Journal of the American Dental Association, 1994) reported side effects in about two thirds of patients, and these settled within 24 to 48 hours.
Using less gel, a desensitising toothpaste and the odd night off usually keeps things comfortable. We cover this further in does teeth whitening hurt and how long sensitivity lasts after whitening. Pain in a single tooth, or pain that does not ease, is different and should be looked at, as it can point to a crack or decay.
The products that do wear teeth down
When someone says whitening ruined their teeth, the cause is often a product or habit that works quite differently from peroxide gel.
Charcoal powders and some very abrasive whitening pastes remove surface stain by scrubbing. Used every day, they can wear enamel and the softer root surfaces near the gumline. Our article on charcoal whitening looks at the evidence. Lemon juice, apple cider vinegar and strawberry pastes are acidic, and rubbing them on teeth can soften enamel; we go through these in natural whitening remedies.
Peroxide itself can cause problems when it is overused. Leaving gel on much longer than instructed, combining products, or repeating courses back to back to chase a lighter shade tends to bring sore teeth and gums rather than a better result. Our guide to how often you can whiten safely explains sensible spacing.
Strength matters too. Under Schedule 10 of the Poisons Standard, whitening products containing more than 6% hydrogen peroxide or 18% carbamide peroxide may only be sold, supplied and used by registered dental practitioners. Kits bought online with unclear or missing labels make it hard to know what you are applying, as explained in are at-home whitening kits safe.
Check for erosion before you start
Whitening does not cause erosion, but erosion that is already there affects whitening. Where enamel has thinned, more dentine shows through, so teeth can look more yellow to begin with and are often more sensitive during treatment.
Acidic drinks, reflux, frequent vomiting and grinding are common causes. Signs a dentist looks for include cupped or rounded biting surfaces, glassy see-through edges and yellow patches near the gums. Whitening may still be possible with a gentler gel and a slower schedule, or it may be better to deal with the cause first. More detail is in whitening teeth with enamel erosion and enamel erosion causes and prevention, and people who clench or grind can read teeth whitening if you grind your teeth.
Habits that keep a whitening course gentle
- Have a check-up first so decay, cracks, gum problems and worn areas are found before whitening.
- Use a gel of known strength in trays made to fit, and stick to the wear time you are given.
- Keep brushing with fluoride toothpaste during the course and after it.
- Go easy on acidic drinks around whitening sessions.
- Space full courses months apart and use short top-ups to maintain the colour.
A dentist or oral health therapist can check your teeth and gums as part of a visit to our general dentistry clinic. Our teeth whitening page describes Lumi Home, Lumi Refresh and Lumi Radiance, which all include dentist-supplied take-home gel, and current offers are on the current deals page. Results vary from person to person, and no particular shade can be promised.
Common questions
Will whitening make my enamel thinner?
No. Peroxide lightens the colour of the tooth through a chemical reaction and does not remove tooth structure when used as directed.
Are stronger dentist gels harder on enamel?
Higher-strength gels act faster, so they are used for shorter times and, in the chair, with the gums protected. The main trade-off is a greater chance of temporary sensitivity, not enamel loss.
If you would like to whiten and are unsure about the state of your enamel, book a check-up with us in Melrose Park and we can assess it first.
