Saturday, August 20, 2005

The importance of caring for your teeth -

Teeth�singular tooth�are hard structures found in the jaws of many vertebrates. They have various structures to allow them to fulfill their many different purposes. The primary function of teeth is to tear and chew food and in some animals, particularly carnivores, as a weapon. The roots of the teeth are covered by gums. Teeth are covered by a protective stucture, called the enamel, that helps to prevent cavities on the teeth. Adult teeth naturally darken as the person matures, the pulp within the tooth shrinks and dentin is deposited in its place.
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The form teeth take and their mode of development in a species is called the species' dentition. Dentists sometimes refer to the inner surface of teeth as the lingual surface (meaning towards the tongue), and the outer surface as the labial surface (meaning towards the lips) or "buccal" (meaning towards the cheek). Other terms are mesial (toward the midline), distal (away from the midline), occlusal (the top surface), incisal (the cutting surface), "gingival" (toward the gumline), and "pulpal" (toward the center).
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Teeth are among the most distinctive features of different mammal species, and one that fossilizes well. Paleontologists use them to identify fossil species and, often, their relationships. The shape of the teeth is related to the animal's diet, as well as its evolutionary descent. For example, plant matter is hard to digest, so herbivores have many molars for chewing. Carnivores need canines to kill and tear and since meat is easy to digest, they can swallow without the need for molars to chew the food well.
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Humans grow two sets of teeth, though some animals grow many more: sharks grow a new set of teeth every two weeks. Some other animals grow just one set. Rodent teeth grow and wear away continually through the animal's gnawing, maintaining constant length. Milk teeth evenly distributed across the quadrants
Enlarge Milk teeth evenly distributed across the quadrants.
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In humans, the first (a.k.a. milk, primary or deciduous) set of teeth appears at about six months of age. This stage is known as teething and can be quite painful for an infant. Human children have 20 milk teeth evenly distributed across the quadrants. Each quadrant of 5 teeth consists of:
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The second, permanent set is formed between the ages of six and twelve years. The new set replaces the 20 teeth of the old set. A new tooth forms underneath the old one, pushing it out of the jaw. Apart from this another 8-12 teeth grow. This set can last for life if cared for properly through a regular program of dental hygiene, including brushing with water or toothpaste as well as periodic professional cleaning by a dentist or hygienist. If a person's teeth are susceptible to decay, for example if the molars include deep pits and fissures, then complete prevention of decay may require treatment with dental sealants.
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Plaque is a soft white layer which forms on teeth, containing large amounts of bacteria of various types, particularly Streptococcus mutans. Left unchecked for a few days plaque will harden, especially near the gums, forming tartar.
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Certain bacteria in the mouth live off the remains of foods, especially sugars. In the absence of oxygen they produce lactic acid, which dissolves the calcium and phosphorus in the enamel in a process known as demineralisation. Enamel demineralisation takes place below the critical pH of about 5.5.
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Saliva gradually neutralises the acids causing the pH of the tooth surface to rise above the critical pH. This causes 'remineralisation', the return of the dissolved minerals to the enamel. If there is sufficient time between the intake of foods (two to three hours) and the damage is limited the teeth can repair themselves.
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Dental caries (cavitation) occurs when over a period of time the process of demineralisation is greater than remineralisation. Attempts to prevent dental caries involve reducing the factors that cause demineralisation, and increasing the factors leading to remineralisation. Unchecked demineralisation leads to cavities, which may penetrate the underlying dentine to the tooth's nerve-rich pulp and lead to toothache.
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In moderation, fluoride is known to protect the teeth against caries. It toughens the teeth by replacing the hydroxyapatite and carbonated hydroxyapatite minerals of which the enamel is made with fluorapatite, which is harder to dissolve by acid. It also reduces the production of acids by bacteria in the mouth by reducing their ability to metabolize sugars. The addition of fluoride (sodium monofluorophosphate) to toothpaste is now very common, and may explain the decline in dental caries in the Western world in the past 30 years.
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Some believe that a diet rich in fluorine salts, particularly in childhood, can lead to a stronger enamel which is less susceptible to decay. Fluoridation of drinking water remains a controversial issue. However, in many parts of the world, the natural water supply may be sufficiently rich in fluorides to supply the needs of children without additional sources being required.
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Caries may be treated by filling cavities with a long-lasting material. This was, traditionally, achieved using gold or a compound of metals called amalgam, which contains mercury. For cosmetic reasons, and because it is thought mercury may seep from fillings into the circulation over time, a ceramic or other white filler may be preferred to amalgam. As a last resort, teeth affected by caries may be extracted, preferably under local or general anaesthetic.