How Teeth Whitening Works
All effective teeth whitening uses peroxide chemistry. Either hydrogen peroxide or carbamide peroxide (which breaks down to release hydrogen peroxide) penetrates the enamel and dentine, oxidising the chromogen molecules responsible for staining. This produces a visible lightening of the tooth colour.
The result depends on three factors: the peroxide concentration, the contact time and the initial cause of the staining. Extrinsic stains (from coffee, tea, red wine, tobacco) respond well to peroxide whitening. Intrinsic stains (from tetracycline antibiotics taken during tooth development, fluorosis, trauma) respond poorly or not at all.
Professional In-Chair Whitening
What it involves: A dental professional applies a high-concentration hydrogen peroxide gel (up to 25% to 40% depending on the country's regulations) to the tooth surfaces with a protective barrier on the gums. Some protocols use a light (LED or UV) to activate the peroxide.
Results: 4 to 8 shade improvements measurable on a whitening scale in a single session. The most dramatic and fastest results of any whitening method.
Duration: 1 to 2 hours in the dental chair.
Cost: £300 to £1,000 in the UK, $300 to $1,500 in the USA, highly variable globally.
Side effects: Temporary tooth sensitivity during and immediately after the procedure. Some patients experience gum irritation at the contact point. Both effects resolve within 24 to 48 hours in most cases.
Who it suits: Anyone with healthy enamel and no significant restorations in the front teeth (crowns, veneers and white fillings do not whiten; you would be left with non-matching restorations after whitening natural teeth).
At-Home Whitening With Professional Trays
What it involves: A dentist takes impressions of your teeth and provides custom-fitted plastic trays. You apply a lower-concentration peroxide gel (10% to 22% carbamide peroxide) to the trays and wear them for 2 to 8 hours per day.
Results: Comparable final results to in-chair whitening achieved over 2 to 4 weeks.
Cost: £200 to £500, significantly less than in-chair for comparable final results.
The advantage over in-chair: The slower application produces less sensitivity in most patients. Custom trays also allow touch-up treatments using the same trays with additional gel purchased later.
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Whitening Strips
Products: Crest Whitestrips (USA), Oral-B 3D Whitestrips (UK/EU)
Peroxide concentration: Regulated at 0.1% hydrogen peroxide maximum in the EU. USA OTC products use up to 10% hydrogen peroxide.
Results: Noticeable improvement in 2 to 4 shades over a 2-week course at USA concentrations. EU-regulated products show more modest results due to lower peroxide limits.
Application: Apply strips to the front teeth for 30 to 45 minutes per application. Most courses run 14 to 21 days with one or two applications per day.
The EU regulation limit: The 0.1% limit in EU countries means EU whitening strips and whitening toothpastes produce limited whitening through peroxide alone. EU products rely more heavily on optical whitening agents (which make teeth appear whiter in the moment without actual whitening) and abrasive polishing agents.
Whitening Toothpastes
How they work: Primarily through abrasive polishing (removes surface stains) and, in some products, low-concentration peroxide. They do not penetrate enamel for intrinsic whitening.
Realistic results: Effective at removing surface staining from coffee, tea and food. Do not produce shade changes on intrinsically darker teeth. Useful for maintenance after professional whitening.
The abrasive concern: Whitening toothpastes use Relative Dentin Abrasivity (RDA) values that measure how aggressively they polish. High-RDA whitening toothpastes (above 150) remove stains effectively but also remove a small amount of enamel with each use. Daily use of high-RDA products over years contributes to enamel thinning.
Look for whitening toothpastes with an RDA below 100 for daily use. Products from Sensodyne, Colgate Max White One and Oral-B contain hydroxyapatite or low-abrasive formulas that clean without aggressive enamel removal.
Products That Do Not Whiten
Charcoal toothpaste and powder: No evidence for intrinsic whitening. The abrasive particles remove surface staining but studies show no improvement over standard low-abrasive toothpaste for shade change. The high abrasivity of many charcoal products (RDA above 150) poses enamel thinning risk.
Oil pulling: No clinical evidence for teeth whitening. The mechanical action of swishing oil may reduce some surface bacteria but produces no peroxide-related whitening effect.
Lemon juice and baking soda: Highly acidic (lemon juice, pH 2.2) applied directly to enamel causes demineralisation. Baking soda alone is mildly abrasive but not bleaching. This combination is not recommended.
Sensitivity Management During Whitening
Tooth sensitivity is the primary side effect of all peroxide whitening. The hydrogen peroxide enters the dentine tubules and stimulates nerve endings, producing a sharp, cold sensitivity.
Management strategies:
- Use a potassium nitrate or stannous fluoride toothpaste (Sensodyne) for 2 to 4 weeks before starting whitening
- Apply desensitising gel (included with most professional whitening kits) after each whitening session
- Reduce whitening frequency if sensitivity is significant; results at reduced frequency are slower but still achieve the same endpoint
- Avoid cold drinks and foods for 48 hours after an in-chair session