How does teeth whitening work?
Most professional whitening uses hydrogen peroxide or carbamide peroxide, which breaks down to release hydrogen peroxide. These agents pass into the enamel and the dentin beneath it and break down coloured molecules that cause discolouration. The structure of the tooth is not removed; the colour of the stain molecules is changed so the tooth appears lighter.
This is different from whitening toothpastes, which mainly remove surface stains through mild abrasion and do not change the natural shade of the tooth.
What causes teeth to discolour?
- Surface (extrinsic) stains from coffee, tea, red wine, curry, smoking and some foods. These often respond well to whitening.
- Age-related yellowing, as enamel thins and the darker dentin shows through. This also commonly responds.
- Internal (intrinsic) discolouration from certain medications taken during tooth development, excess fluoride during childhood, injury or a tooth that has had its nerve die. These are harder to whiten and may need other approaches.
What happens before whitening?
A dental examination is an important first step. Whitening gel applied over untreated cavities, cracked teeth or inflamed gums can cause sensitivity or irritation. Your dentist will check for:
- Decay that should be treated first with cavity treatment.
- Gum inflammation or tartar, which is usually cleaned with scaling before whitening.
- Existing crowns, veneers or fillings in visible areas, which will not change colour.
- Exposed roots or worn enamel that may increase sensitivity.
The starting shade is recorded so you can compare results.
What are the types of professional whitening?
In-office whitening
The gums are protected with a barrier, and a higher-concentration gel is applied to the teeth. A light or activation device may be used depending on the system. At Seoul E&D Dental Clinic, in-office teeth whitening is carried out with a KFDA-approved whitening device. A session commonly takes around an hour, and more than one session may be recommended.
At-home whitening with custom trays
Custom-fitted trays are made from impressions of your teeth, and you wear them with a lower-concentration gel for a set time each day over a period of weeks. This approach is gradual and can be easier to control for sensitive patients.
Combined approach
Some patients start with an in-office session and continue with trays at home, which can help the result develop more evenly.
How white will my teeth get?
Results vary considerably. Natural tooth colour, the type of staining, enamel thickness and how consistently aftercare is followed all affect the outcome. Yellowish discolouration generally responds more readily than greyish discolouration. A reasonable goal is a natural-looking, brighter shade that suits your face and skin tone, rather than an artificially uniform white. Your dentist can give a realistic expectation after the examination, but no one can promise a specific shade.
Does whitening cause sensitivity?
Temporary sensitivity is the most common side effect. Many patients notice brief, sharp twinges, especially to cold, during or in the first day or two after treatment. It usually settles on its own. To reduce it, your dentist may:
- Use a desensitising agent before or after treatment.
- Recommend a toothpaste for sensitive teeth in the weeks before whitening.
- Adjust the gel concentration or session length.
- Suggest spacing out at-home sessions.
Mild gum irritation can also occur if gel contacts the gums, and it typically resolves quickly. If you already have significant sensitivity, see our page on tooth sensitivity treatment first.
Is professional whitening safe?
When carried out under dental supervision with appropriate products, whitening is widely regarded as safe for adult teeth. It is generally not recommended during pregnancy or breastfeeding, mainly as a precaution, and is usually postponed for younger patients whose teeth are still developing. Over-the-counter or unregulated products used without guidance carry a higher risk of gum burns and uneven results.
How long do results last?
Whitening is not permanent. Results commonly last from several months to a couple of years, depending largely on diet, smoking and oral hygiene. Many patients use occasional top-up treatments with custom trays. To help results last:
- Limit coffee, tea, red wine and other strongly coloured foods, especially in the first two days after whitening.
- Rinse with water after staining drinks.
- Avoid smoking.
- Keep up regular cleaning and check-ups.
Can I whiten just one dark tooth?
A single tooth that has darkened is often a sign that its nerve has been damaged, for example after an old injury. Such a tooth may need root canal treatment before anything else, and it may not respond to standard whitening applied from the outside. In some cases, a technique called internal bleaching, where whitening material is placed inside the treated tooth, or a restoration may be considered. An X-ray helps the dentist decide.
Who should postpone or avoid whitening?
- People with untreated decay, gum disease or cracked teeth, until these are addressed.
- Those who are pregnant or breastfeeding, as a precaution.
- Patients with significant existing sensitivity or exposed roots, until the cause is managed.
- Anyone whose main concern is the colour of crowns or fillings, which whitening will not change.
What if whitening is not enough?
For intrinsic stains, uneven patches, chipped edges or old discoloured fillings, whitening alone may not give the result you want. Composite bonding or aesthetic bonded restorations can change the colour and shape of individual teeth. Because restorations do not change colour with whitening, many dentists suggest whitening first and then matching any new restorations to the lighter shade.
Whitening at E&D Dental in Sanbon
We begin with an examination, explain whether whitening is likely to help your type of discolouration, and talk through in-office, at-home and combined options. The clinic is in Sanbon-dong, Gunpo, about a five-minute walk from Sanbon Station on Line 4, with evening hours on Mondays and Thursdays. To ask about whitening, please contact the clinic or read about your first visit.