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 structure, 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.
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).
In Humans
In Aardvarks
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.
While humans only have two sets of teeth, 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.
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.
Adult humans have 32 teeth evenly distributed across the quadrants. Each quadrant of 8 teeth consists:
The teeth are numbered, in the most common American system, 1-16 and 17-32, with 1 being the upper right wisdom tooth (whether or not it is present) and 32 being the lower right wisdom tooth.
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.
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.
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.
In moderation, Fluoride is known to protect the teeth against cavities. 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.
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.
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 contained mercury. Amalgam fillings, however, released traces of mercury and were cosmetically not very appealing. Nowadays tooth-colored Composite or ceramic are used in addition to traditional gold fillings.
As a last resort, teeth affected by caries may be extracted, preferably under local or general anaesthetic.
Sucrose (table sugar) is most commonly associated with caries, although Glucose and Maltose seem equally gervic (likely to cause caries). The amount of sugar consumed at any one time is less important than how often sugar containing foods and drinks are consumed. The more frequently sugars are consumed, the greater the time during which the tooth is exposed to low pH levels, at which demineralisation occurs. It is important therefore to try to encourage infrequent consumption of food and drinks containing sugar so that teeth have a chance to repair themselves. Obviously, limiting sugar-containing foods and drinks to meal times is one way to reduce the incidence of caries.
Artificially refined sugar is not the only type that can promote dental caries. There are also sugars found in fresh Fruit and fruit juices. These foods (oranges, lemons, limes, apples, etc. ) also contain acids which lower the pH level. On the other hand, Carbonic acid found in soda water is very weakly acidic (pH 6.1), and not associated with dental caries (provided the soda is sugar free, of course). That said, soda is not as healthy for the teeth as milk, due to its lower pH and lack of calcium. Drinking sugared soda throughout the day raises the risk of dental caries tremendously.
Another factor which affects the risk of developing caries is the stickiness of foods. Some foods or sweets may stick to the teeth and so reduce the pH in the mouth for an extended time, particularly if they are sugary. It is important that teeth are cleaned at least twice a day, preferably with a Toothbrush and fluoride toothpaste, to remove any food sticking to the teeth. Regular brushing and the use of dental floss also removes the dental plaque coating the tooth surface.
Brushing teeth immediately after eating sugar is not recommended, because sugar softens the enamel, which can then be damaged by brushing. It is better to wait half an hour after eating sugary foods before brushing.
Electric toothbrushes are no more effective than the manual variety, according to research. However, "rotation-oscillation" electric toothbrushes out-performed manual brushing, removing around 7% more plaque and leading to 17% less gum disease than manual brushes. Any kind of electric toothbrush does tend to help people who are not as good at cleaning their teeth and as a result have had oral hygiene problems.
As noted above, eating certain cheeses such as cheddar soon after eating potentially harmful foods have been noted to be helpful in preventing tooth decay as well.
In the future, tooth decay may be banished by treatment with a genetically modified bacterium, according to research at the University of Florida.
Some of the earliest artificial teeth were made by the Etruscans and their use was adopted in Ancient Rome for the wealthy citizens who often dined on food containing damaging sugars.