Teeth whitening is one of the most asked-about procedures in dentistry, and one of the most surrounded by misinformation. It is worth separating what works from what harms the tooth.
Why do teeth go yellow?
Discolouration falls into two groups. External stains come from tea, coffee, smoking, red wine and some mouthwashes; they cling to the tooth surface and mostly come off with professional cleaning. Internal discolouration is within the tooth: the enamel thinning with age so the yellow dentine beneath shows more, certain antibiotics taken in childhood, excessive fluoride, or the tooth losing its vitality after a blow.
Whitening gels act on both external and internal discolouration, but not all of it responds equally. Yellow tones usually lighten well; grey and brown tones are more resistant.
How does whitening work?
The active ingredient in whitening gels is hydrogen peroxide or carbamide peroxide. These pass through the pores of the enamel and break down the large molecules that give colour. No tooth substance is removed and the enamel is not worn away; only the colour pigments are lightened.
In the clinic or at home?
- In-clinic whitening: A high-concentration gel is applied by the dentist with the gums protected. Results in about an hour.
- Home whitening: A low-concentration gel is placed in trays made for you and worn for a set time every day for a few weeks. Results come more slowly but in a controlled way.
- Combined: Started in the clinic and supported with trays at home. Chosen for a longer-lasting result.
Details of the methods are on our teeth whitening and cleaning page.
Is it safe?
Carried out under a dentist's supervision, at the recommended concentration and for the recommended time, whitening does not cause lasting damage to the enamel. The possible side effects are temporary:
- Tooth sensitivity: The most common side effect; twinges with cold pass within a few days.
- Gum irritation: Caused by gel touching the gum; prevented in the clinic with a protective barrier.
Whitening is not done during pregnancy or breastfeeding, for anyone under 18, or for people with untreated decay or gum disease.
Home remedies: baking soda, lemon, charcoal
Methods recommended online such as baking soda, lemon juice, vinegar, activated charcoal and salt do not whiten teeth; they wear away the enamel. Worn enamel becomes thinner, more of the yellow dentine shows through, and over time the tooth becomes yellower and more sensitive. Worn enamel does not come back.
Whitening toothpastes sold in shops only reduce surface stains a little; they do not lighten the tooth's own colour. Long-term use of highly abrasive ones can cause sensitivity.
How long does the effect last?
The result is not permanent, but it lasts: between six months and two years for most people. Your habits decide how long.
- Avoid staining foods and drinks for the first 48 hours; teeth take up colour more readily in that time.
- Cut down on tea and coffee, or drink water afterwards.
- Stop smoking; it is the strongest cause of staining.
- Have your teeth cleaned every six months.
- Top up briefly with home trays at the intervals your dentist recommends.
Frequently asked questions
How many shades lighter will my teeth get?
It depends on the starting colour and the type of discolouration. Most people gain several shades; an exact result cannot be guaranteed in advance.
Do fillings and crowns whiten?
No. Whitening only acts on natural tooth tissue. If you have fillings or crowns on your front teeth, a colour difference may appear after whitening and they may need replacing.
How often can whitening be repeated?
Under a dentist's supervision, generally no more than once a year. Your dentist decides how often according to your sensitivity and how quickly your teeth stain.
This article is for general information and is not a substitute for diagnosis or treatment. If you have a complaint, please see your dentist.