Enamel is the outer layer of the exposed tooth. It is a hard thin translucent layer of calcified substance that envelops and protects the dentin (the main portion of the tooth structure) of the crown of the tooth.
Enamel is the hardest substance in the body and is almost entirely composed of calcium salts. The hardness of enamel is an important property as the main role of enamel is to protect the softer underlying dentin of the tooth. Enamel also serves as the surface for chewing grinding and crushing of food and this is another reason for its hardness.
Enamel has the highest concentration for any structure in the body of mineral at ~90%. The proteins in enamel are not found elsewhere and they are called enamelins and amelogenins. The high mineral content (mature enamel has no cells and is not alive) makes it the hardest component and also most resistant to bacterial attack since there is little organic matter present. A flaw of enamels hardness though is that it is prone to chipping and splitting as it is a brittle substance.
Enamel is translucent (semi-transparent) and ranges in color from yellow to gray-white with the range of colors due to varying thickness of enamel. Enamel is composed of thin rods (enamel prisms) held together by a cementing substance and surrounded by an enamel sheath. The rods that make up enamel are formed themselves by cells known as ameloblasts.
Problems with tooth enamel are associated with tooth decay. Tooth decay is the interaction of specific bacteria (found in plaque) sugar and a susceptible tooth surface. Bacteria cause plaque which feed on sugars in food such as glucose fructose maltose and lactose. The bacteria in the plaque use sugar as a source of energy and as bacteria digest the sugar and a by-product is excreted. This by-product is extremely acidic and starts to demineralise enamel (lose of calcium and minerals from the enamel). As the enamel loses its minerals it starts to break down. This is the start of a cavity.
Acid produced by the bacteria is excreted right against the surface of the tooth and immediately starts attacking the enamel. Teeth with ﾔnooks and cranniesﾔ will trap more food than those with smoother surfaces and lead to more decay. Teeth that have just emerged such as those of children and young adults have enamel that is not yet very strong and are thus highly susceptible to acid attack.
The use of dental sealants is a good means of decay prevention. Sealants are thin plastic-like coating applied to the chewing surfaces of the molars. This coating prevents the accumulation of plaque in the deep grooves on these vulnerable surfaces. Sealants are usually applied on the teeth of children shortly after the molars erupt. Older people may also benefit from the use of tooth sealants. Fluoride is also often recommended to protect against tooth decay and using toothpaste with a good amount of fluoride is essential.