Dental bleaching also known as tooth whitening, is a common procedure in general dentistry but especially in the field of cosmetic dentistry. A child's deciduous teeth are generally whiter than the adult teeth. As a person ages the adult teeth often become darker due to changes in the mineral structure of the tooth, as the enamel becomes less porous. Teeth can also become stained by bacterial pigments, foodstuffs and tobacco. Certain antibiotic medications (like tetracycline) can also lead to teeth stains or a reduction in the brilliance of the enamel.
There are two methods to whiten teeth-bleaching gel and laser bleaching. Traditionally, at-home whitening is done with bleaching gel which is applied to the teeth using thin guard trays. Oxidizing agents such as hydrogen peroxide or carbamide are utilised to lighten the shade of the tooth. The oxidizing agents oxidize the porosities in the rod-like crystal structure of interprismatic stain deposits; over a period of time, the dentin lying underneath the enamel is also bleached. Laser bleaching utilizes light energy to accelerate the process of bleaching in a dental clinic. The effects of bleaching can last for several months, but may vary depending on the lifestyle of the patient. Factors which will decrease whitening include smoking and the ingestion of dark coloured liquids like coffee, tea and red wine.
Internal staining of dentin can discolour the teeth from inside out. Internal bleaching can remedy this. If heavy staining or tetracycline damage is present on a patient's teeth and whitening is ineffective, there are other methods of whitening teeth. Bonding, when a thin coating of composite material is applied to the front of a person's teeth and then cured with a blue light. This can be performed to mask the staining. A veneer can also mask tooth discolouration.
The mechanism of bleaching involves free radicals and breakdown of pigment whereas whitening is accomplished by abrasive action as in dentrifices. Tooth bleaching agents may be used for external or internal bleaching performed in the clinic by a dentist or at home by a patient.
Internal bleaching procedures are performed on devitalized teeth that have undergone endodontic therapy but are discoloured due to internal staining of the tooth structure by blood and other fluids. Unlike external bleaching which brightens teeth from the outside in, internal bleaching brightens teeth from the inside out. Bleaching the tooth internally involves drilling a hole into the pulp chamber, cleaning, sealing and filling the root canal with a rubber- like substance, and placing a peroxide gel into the pulp chamber so that the gel can work directly inside the tooth on the dentin layer. Internal bleaching is always performed in the dental clinic. Seldom produces reliable results when used to eliminate intrinsic stains in dentin. There are two common approaches to internal bleaching:
Mechanism of action: Sodium perborate powder decomposes into sodium metaborate and hydrogen peroxide thus releasing nascent oxygen. The sodium perborate powder that is mixed with hydrogen peroxide also releases nascent oxygen. This combination is thought to be synergistic and very effective in bleaching.
Is indicated for teeth that are discoloured from ageing, fluorosis or tetracycline staining. It can be applied by the dentist or by the patient. Dentist applied bleaching can be divided into:
| Colour of Stain/ Etiology | Ease or difficulty of bleaching |
| Fluorosis | Degree of difficulty depends on extent of fluorosis. |
| Blue-grey | |
| Dentinogenesis imperfecta, erthroblastosis foetalis, tetracycline | Deeply stained blue-grey discolourations, especially by tetracycline are more difficult to treat than yellow stains. |
| Yellow | |
| Fluorosis, physiologic changes due to ageing, obliteration of the pulp chamber | Mild uniform yellow discolouration associated with ageing or mild uniform fluorosis are the easiest to treat. |
| Brown | |
| Fluorosis, caries, porphyra, tetracycline, dentinogenesis imperfecta | Stains that are deeper in colour are difficult to treat. |
| Grey | |
| Silver oxide from root canal sealers | Dark stains from root canal sealers are seldom bleachable; should be treated restoratively. |
| Black | |
| Mercury stains (amalgam), caries, fluorosis | Very dark or black stains from silver- containing root canal sealers or from mercury are seldom bleachable; should be treated restoratively. |
| Pink | |
| Internal resorption | Bleaching is not indicated; treatment consists of endodontics and calcium hydroxide. |
| Beverages | |
| Coffee and tea | May compromise with treatment results. |
| Use of liquor | May possibly result in additive carcinogenicity as peroxides have mutagenic potential. It may also compromise in treatment. |
| Tobacco | |
| Tobacco use | May possibly result in additive carcinogenicity as peroxides have mutagenic potential. It may also compromise in treatment. |
| Precautions | Adverse efffects |
| General | |
| Patient should not smoke or use any kind of potential carcinogen | Prolonged use of 30% or higher H2O2 can destroy cells and for cells that are not destroyed prolonged use may increase the carcinogenic effect. |
| Oral | |
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Patient with root sensitivity should avoid the treatment as it may aggravate sensitivity In cases of tissue burns rinse the affected area for 1-5 mins |
Acidic nature of some products may produce transient dentin sensitivity. |
Various chemical and physical agents can be used to whiten teeth. Toothpaste typically has small particles of silica, aluminum oxide, calcium carbonate or calcium phosphate to grind off stains formed by coloured molecules that have lodged onto the teeth from food. Unlike bleaches, whitening toothpaste does not alter the intrinsic colour of teeth. Bleaching solutions contain peroxide which bleaches the tooth enamel to change its colour. Off-the-shelf products typically rely on a carbamide peroxide solution varying in concentration from 10% to 22%. Bleaching solutions may be applied directly to the teeth, embedded in a plastic strip that is placed on the teeth or use a gel held in place by a mouthguard. Because the concentration is less to avoid toxicity, whitening often takes several weeks.
Whitening treatments used by dentists are much more concentrated, containing substances with more than 30% hydrogen peroxide and require protection of the soft tissues.
