Compositions for cleaning teeth have been known for a long time—Hippocrates (430–377 B.C.E.) recognized the value of powdered marble (calcium carbonate) for cleaning teeth, and this compound in various forms has been used ever since. In the Middle Ages, various strange mixtures, often with names such as Magistery of Pearls, Dragon’s Blood, and Powdered Crab’s Eyes, were rubbed onto the teeth to make them look cleaner and sweeten the breath.
Prophylactic toothpastes
The latter half of the 20th century saw the function of toothpaste change from being purely cosmetic to prophylactic—disease-preventing. Modern toothpastes have three functions: they remove plaque, the sticky film that harbors decay-causing bacteria; they strengthen tooth enamel against acid attack; and they contain components that enable teeth to repair themselves by a process of remineralization.
Compositions
Toothpastes neither bleach nor alter the natural color of the teeth; they clean by removing the accumulated film from the surface and may also heighten the luster by polishing.
The most important cleaning and polishing agent in toothpastes is an insoluble mineral powder. Often this is calcium carbonate, which is mildly abrasive as well as being an antacid, or it may be a phosphate salt, a hydrated aluminum oxide, or especially in the clear-gel types of toothpastes, a silicate or silica gel. The precise shape and size distribution of the particles are carefully controlled by the manufacturer both to get the best cleaning effect when the particles are brushed over the surface of the tooth and to make sure that the teeth will not be damaged. The part of the tooth normally above the gum margin, the crown, is covered with a hard layer of enamel. Beneath the enamel of the tooth crown is a softer tissue called dentine. Particularly in older people, the dentine of the tooth root may sometimes be exposed along the margins of the gums, and so toothpaste must be able to clean this soft dentine as well as the harder crown enamel without damaging either. A good polish on the teeth is important not merely for appearance but also because it will reduce the ease with which bacteria can anchor themselves to the tooth surface.
In addition to the cleaning and polishing constituents, toothpastes today usually contain a water-binding material (humectant), such as glycerine or sorbitol, to help keep the paste moist in the tube. A detergent, such as sodium lauryl sulfate, might be included to help loosen bacterial plaque and food debris. Thickening agents such as natural gums, celluloses and alginates are added to prevent the liquid and solid phases in the toothpaste from separating by acting as hydrophilic colloids, and saccharin and flavoring make the paste taste pleasant.
Because toothpaste is intended to be used regularly, it provides a simple method of treating teeth with beneficial, biologically active compounds. Fluoride in various forms is widely used in toothpaste to give protection against dental decay.
