Two kinds of stain, and why the difference matters
- Extrinsic stain
- Stain on the outside of the tooth from coffee, tea, red wine and tobacco. A cleaning at a hygiene appointment removes much of it, so a brown film along the gum line may not need whitening at all.
- Intrinsic stain
- Color inside the dentine, under the enamel. Enamel thins with age and the yellower layer beneath shows through, and old trauma and some medications change color from within. Peroxide reaches this, gradually.
- Tetracycline banding
- Grey, blue or brown bands laid down when the antibiotic was taken during tooth development. It responds poorly. Months of nightly trays lighten some cases a little, and many need veneers instead.
- One dark tooth
- A tooth darkened after injury or root canal therapy is discolored from the inside, so gel on the outside does little. Internal bleaching suits some root treated teeth, and otherwise the answer is a veneer on that tooth.
How professional teeth whitening actually works
Every product that works contains hydrogen peroxide, or carbamide peroxide which breaks down into it. The molecule passes through enamel into dentine, where it breaks large pigmented molecules into smaller ones that reflect more light. Nothing is painted on or stripped off.
How much change you get is concentration multiplied by contact time. In-office gel is strong and used in short timed cycles with the gums protected, while take-home gel is weaker and worn far longer. Custom trays hold it against enamel and off the gum, where it does nothing but sting.
Whitening lightens, it does not standardize. White spots often look more obvious partway through, the translucent biting edge stays translucent, and every tooth has a ceiling nobody can predict. The starting shade is recorded so before and after is measured rather than remembered.
In-office whitening or custom take-home trays
Both use peroxide and both work. They differ in strength, in how long it takes, and in who controls it.
| Consideration | In-office session | Custom take-home trays |
|---|---|---|
| How it is done | Strong gel in the chair with the gums isolated | Weaker gel in trays made from impressions of your teeth, worn daily |
| Time to a result | Visible change on the day | Builds over one to two weeks, longer for stubborn stain |
| Sensitivity | More likely to spike, settling in a day or two | Milder, and controlled by spacing the sessions |
| Touch-ups | Another appointment each time | You keep the trays, so a night or two maintains the shade |
Strips, charcoal and whitening toothpaste
Some of it works, some does nothing, and a little of it does harm.
- Whitening strips contain real peroxide and they genuinely lighten teeth, for less money. One shape has to fit every mouth, so coverage is uneven on crowded teeth, and nobody has looked in your mouth first.
- Whitening toothpaste works by abrasion. It lifts surface stain and does not change the color inside the tooth, and the more abrasive formulations wear exposed root surfaces.
- Charcoal powders, lemon juice and vinegar. Charcoal is abrasive and there is no good evidence it alters color inside a tooth. Acid makes teeth look briefly lighter by frosting the surface, and it dissolves enamel, which does not come back.
- Kiosk and salon whitening. No examination, no medical history, and nobody trained to spot an untreated cavity before gel goes over it.
Sensitivity, safety and keeping the result
Peroxide passes through enamel and dentine and briefly irritates the nerve inside the tooth, felt as sharp cold sensitivity or short twinges with no obvious trigger. For most people it is temporary and stops when treatment stops.
It is manageable. Potassium nitrate gel in the tray calms the nerve, fluoride blocks the microscopic tubules in dentine, and shortening or spacing sessions works without costing you the end result. Pushing through severe pain is not the plan.
An examination first is not a formality. Whitening will not fix a cracked tooth, and gel reaching an untreated cavity is a fast route to real pain. Afterwards the color drifts back gradually, faster for coffee and red wine drinkers, so most tray users top up for a night or two every few months.
Teeth whitening questions we get asked
How white will my teeth actually go?
That cannot be predicted precisely, and anyone quoting a number in advance is guessing. Yellow-toned teeth generally respond better than grey, and evenly colored teeth better than banded ones.
How much does teeth whitening cost?
It depends on the method and whether new trays are made, and you get the figure before anything starts. Whitening is cosmetic, so it is usually not a benefit under a dental plan. See insurance.
Is whitening safe for enamel?
Peroxide whitening has been in routine dental use for decades and, used as directed under supervision, the effect most people notice is temporary sensitivity. Problems usually trace back to overuse, acidic home remedies or abrasive powders.
Will it work on my crown or my white filling?
No, neither lightens. If a front tooth restoration is what no longer matches, the sequence is whitening the natural teeth first, then replacing that restoration to the new shade. See porcelain crowns.