Tooth

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Types of teeth
  • Molars are used for grinding up foods
  • Carnassials are used for slicing food. In carnivores only.
  • Premolars are similar to molars but smaller and sometimes called "bicuspids"
  • Canines are used for tearing apart foods and sometimes called "cuspids"
  • Incisors are used for cutting foods

Teeth (singular: tooth) are 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).

Types of tissue in teeth

In Humans

  • Enamel is a hard outer layer consisting of calcium and phosphate.
  • Dentin is the inner layer, the bulk of the tooth.
  • Pulp is the core, containing nerves and blood vessels.
  • Cementum is the thin layer around the root; a bone-like material which connects the teeth to the jaw.


In Aardvarks

  • Teeth lack enamel and have many pulp tubules, hence the name of the order Tubulidentata.

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 have 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.


Contents

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Human teeth

Image:ToothSection.jpg Humans grow two sets of teeth. The first (a.k.a. baby, milk, primary or deciduous) set of teeth appears at about six months of age, although some babies are born with one or more teeth already visible. 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

  • a central incisor
  • a lateral incisor
  • a cuspid (a.k.a. canine)
  • a first molar
  • a second molar

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 permanent teeth evenly distributed across the quadrants which are made of different tissue that are often mistakingly confused for bone. It is true that teeth are attached to the underlying bone of the jaw (via a ligament called the periodontal ligament, though the teeth themselves have no bone component to them. If your teeth were made of bone, they would grind away extremely quickly. The white part of the tooth which can be seen in the mouth is enamel. Immediately 1-3mm below this layer of enamel is a slightly softer, yellow tissue called dentine. Dentine is supported by the pulp (commonly called 'the nerve' - although it contains many other structures which are not nerves), which lies in the centre of the tooth.

It is worth noting that the third molars (wisdom teeth) are the final teeth to erupt in the human dentition (usually at around the age of 20). However, it is common for the wisdom teeth not to erupt at all - this is often the case in people with small jaws, as there is not enough room in the jaw to support the extra teeth. Additionally, it is possible, though rare, for a person to have 4th molars, and there have been instances where 5th molars have been present in the dentition.

Each quadrant of 8 teeth consists of these types of tooth:

  • central incisor
  • lateral incisor
  • cuspid (a.k.a. canine)
  • first premolar
  • second premolar
  • first molar
  • second molar
  • third molar ("wisdom teeth")

The last molar of each quadrant (i.e. the third molar and commonly referred to as wisdom teeth) may or may not erupt.

Dentists, in writing or speech, use several different notation systems for associating information to a specific tooth. The three most commons systems are the Universal Numbering System, Palmer Notation Method, and the two-digit FDI World Dental Federation notation, which is widely used internationally [1].

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Tooth decay

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Plaque

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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.

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 which cause 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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Caries (Cavities)

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This section should be merged into dental cavities.

Image:Dental x-ray.jpg Dental caries (cavitation)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.

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.

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Foods

This section should be merged into oral hygiene.

Most foods endanger teeth to some extent. By far the best protection is brushing after meals and snacks. However, some foods are worse than others.

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Better

Some foods may protect against cavities. Milk and cheese appear to be able to raise pH values in the mouth, and so reduce tooth exposure to acid. They are also rich in calcium and phosphate, and may also encourage remineralisation. Plus, they may increase saliva production, which also increases the pH level in the mouth. Foods high in fiber may also help to increase the flow of saliva. Unsweetened (sugar free) chewing gum stimulates saliva production, and helps to clean the surface of the tooth. Even sugared gum may be helpful, since the sugar dissolves out very quickly.

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Worse

Sugars are commonly associated with dental caries. Other carbohydrates, especially cooked starches, eg crisps, may also damage teeth, although to a much lesser degree. This is because starch is not an ideal food for the bacteria. It has to be converted (by enzymes in saliva) first.

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 food and drinks that contain sugar 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 be 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.

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Tooth care

Image:SpooSpas teeth.jpg Template:Main Regular brushing is recommended by healthcare professionals twice a day. [2]. Studies show that the minimum required time interval is once every two days; however, more frequent recommended brushing is to help maintain a healthy habit in the populationTemplate:Fact. A mirror may be used to visualize if the plaque is completely removed during brushing. The actual term 'brushing' is rather inaccurate. Though a toothbrush is used, it is not designed to deliver mechanical abrasive action. Rather, the surface of the brush is meant to be held at a forty five degree angle to remove plaque from the periodontal margin (the space in between the gum and tooth). Thus, the term 'cleaning teeth' is far more accurate.

In research, levels of plaque were recorded before and after brushing and found that plaque removal steadily improved as brushing times and pressure were increased. However, their results showed that when people brush for longer than two minutes, at a pressure higher than 150 grams (the weight of an orange), they are not removing any additional plaque, and may be causing permanent damage to the teeth and gums.

Brushing teeth immediately after eating acidic foods is not recommended, because acid softens the enamel, which can then be damaged by brushing. It is better to wait at least half an hour after eating acidic foods before brushing. Rinsing the mouth and eating non-acidic foods can also speed up this process.

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. [3] 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. [4]

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Dentures and "false" teeth

In societies that have high sugar diets, tooth decay can damage teeth badly enough that they need to be removed. This leads to the creation of replacement teeth such as dentures and other tooth replacements.

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.

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Abnormalities of the dentition

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Development of teeth

Template:Main There are three stages in the embryonic development of teeth, the Bud Stage, the Cap Stage and the Bell Stage. The Bud stage begins at the 7th week of intrauterine life.

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Facts about teeth in non-human animals

  • Rodents' teeth grow all their lives.
  • Reptiles' and sharks' teeth are replaced constantly, before they wear out. A crocodile replaces its teeth over forty times in a lifetime.
  • Elephants' tusks are specialized incisors for digging food up and fighting.
  • Turtles and tortoises are toothless
  • Narwhals giant unicorn-like tusk is a tooth that contains millions of sensory pathways and may be used for sensing in feeding, navigation and mating. It is the most neurologically complex tooth known.
  • Horse teeth can be used to estimate the animal's age, and some horses have a form of premolars called Wolf teeth.
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See also

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External links

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