Tooth whitening

Tooth whitening, also  known as dental bleaching is a common procedure in dentistry in which chemical agent such as carbamide peroxide is used to lighten the shade of the tooth. Dental bleaching is usually done to get rid of unsightly stains on the teeth.  There are several factors which can cause tooth staining:

1. Food and beverages like coffee, tea and cola, which on the long run causes staining due to its cumulative effect

2. Tobacco products such as cigarettes, cigars, pipes, and even smokeless tobacco which also has cumulative effect.

3. Medications such as tetracycline, a type of antibiotic and its derivative compounds (minocycline and doxycycline) can cause tooth staining if it is ingested during tooth formation period. The compounds of the antibiotic is incorporated into the teeth during development, causing staining of the erupted teeth. Therefore, tetracycline is contraindicated in pregnant women and children below 8 years old.

4. Fluoride, if ingested in large amounts during tooth development, can cause staining. Children have the tendency to swallow toothpaste which contains fluoride. The tooth may appear chalky white or even brown in color. This appearance is also known as ‘mottled enamel’.

5.  Physiological processes such as aging and dental decay
6. Trauma to the tooth can also cause tooth discoloration. An accident, fall or blow to the tooth will sever the blood vessels in the pulp of a tooth. As a result, the tooth becomes necrotic and changes color. The color change is caused by the components of blood from the severed blood vessels. In this case, a root canal treatment has to be carried out first to remove the necrotic pulp and clean the canal before proceeding to bleaching the tooth. 
7. Existing restorations may also cause staining of the tooth. Composite restoration which is tooth color is capable of picking up stains from chromogenic food and beverages. Amalgam restoration can undergo corrosion and cause discoloration at the margins of the restoration.
Before proceeding to dental bleaching, it is important to determine the cause of tooth staining . For example, if the tooth is discolored due to trauma and the pulp has been dead, it is vital to carry out a root canal treatment first  before bleaching the tooth. If an existing restoration has picked up stain over a long period, it is wise to replace the restoration than to bleach the tooth itself. There is no one ‘normal’ shade which is suitable for everyone. Tooth color shade varies according to ethnic and origin. Therefore, the dentist has to carefully evaluate how much whiter the tooth can be after bleaching to suit the patient’s appearance and at the same time fulfill the needs and desire of the patient. 
There are many methods of tooth bleaching:
1. At home bleaching
This is done by the patient himself at home. This involves the use of high or low concentration of gels to bleach the teeth. High concentration gel is more effective than the low concentration gel and it can be used both at home or in the dental office. The gel can be purchased at stores or pharmacies. It is cheaper than in-office bleaching. The procedure is performed using 10%-40% carbamide peroxide placed in a properly fitting plastic tray. The tray should be well fitted to ensure even exposure of the teeth to the gel. The tray is held for 15 to 20 minutes and the procedure is repeated more than two times. This method is relatively quicker and cheaper than in-office bleaching. 
Low concentration gel whitening uses low concentration of carbamide peroxide in plastic trays which are placed next to the teeth for several hours for several days or weeks. It is less effective and the result varies. Other whitening products that can be used at home are chewing gums and toothpastes.
2. In-office bleaching
In office bleaching is carried out by the dentist in his dental office. Before bleaching is done, a layer of protective gel is painted on the gums to prevent chemical burn on the soft tissues. Carbamide peroxide gel is placed in a plastic tray and placed next to the teeth. The plastic tray can be custom made, improving the fit of the tray, resulting in better result. Carbamide peroxide breaks down into hydrogen peroxide. Hydrogen peroxide is the bleaching agent responsible for getting rid of the stains on the tooth surface.
3. Laser bleaching
Laser bleaching is also known as light accelerated bleaching or power bleaching. It uses light energy such as halogen, LED or plasma to accelerate the process of bleaching. This procedure is done in the dental office. A protective layer of gel is applied to the soft tissues to prevent chemical burn. Then 25%-38% hydrogen peroxide is applied to the teeth and exposed to the light source for 6-15 minutes. The light source normally falls within the blue light spectrum. It should have high energy to excite the peroxide molecules but without overheating the pulp as this will cause damage to the pulp tissue. It is a single visit treatment which lasts for half an hour.
4. Internal bleaching
A necrotic or dead tooth may be discolored due to staining by blood products that have leached out from damaged vessels. Such tooth requires root canal treatment before bleaching is carried out. Unlike external bleaching, which lightens teeth from outside in, internal bleaching works the other way round. It works on the dentine, unlike external bleaching agents which works on the enamel layer. After drilling a hole, sodium perborate is placed in the tooth and sealed over a period of days. It can be replaced as needed. This procedure is also known as ‘walking bleach’ technique.