Tooth enamel

Tooth enamel is the hardest and most highly mineralized substance of the body, and with dentin, cementum, and dental pulp is one of the four major tissues which make up the tooth. It is the normally visible dental tissue of a tooth and must be supported by underlying dentin. Ninety-six percent of enamel consists of mineral, with water and organic material composing the rest. The normal color of enamel varies from light yellow to grayish white. At the edges of teeth where there is no dentin underlying the enamel, the color sometimes has a slightly blue tone. Since enamel is semitranslucent, the color of dentin and any restorative dental material underneath the enamel strongly affects the appearance of a tooth. Enamel varies in thickness over the surface of the tooth and is often thickest at the cusp, up to 2.5 mm, and thinnest at its border, which is seen clinically as the cementoenamel junction (CEJ).

Enamel's primary mineral is hydroxyapatite, which is a crystalline calcium phosphate.^[4] The large amount of minerals in enamel accounts not only for its strength but also for its brittleness. Tooth enamel ranks 5 on Mohs hardness scale. Dentin, less mineralized and less brittle, 3–4 in hardness, compensates for enamel and is necessary as a support.

Unlike dentin and bone, enamel does not contain collagen. Instead, it has two unique classes of proteins called amelogenins and enamelins. While the role of these proteins is not fully understood, it is believed that they aid in the development of enamel by serving as a framework support, among other functions.

Tooth bleaching

Dental bleaching, also known as tooth whitening, is a common procedure in general dentistry but most especially in the field of cosmetic dentistry. Many people consider white teeth to be an attractive feature of a smile. A child's deciduous teeth are generally whiter than the adult teeth that follow. 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.^[1]

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 peroxide are utilized to lighten the shade of the tooth. The oxidizing agent penetrates the porosities in the rod-like crystal structure of enamel and oxidizes interprismatic stain deposits; over a period of time, the dentin layer, lying underneath the enamel, is also bleached. Laser bleaching utilizes light energy to accelerate the process of bleaching in a dental office. 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 colored liquids like coffee, tea and red wine.

Internal staining of dentin can discolor 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 laser can be performed to mask the staining. A veneer can also mask tooth discoloration.