Biomedical Engineering Reference
In-Depth Information
1.4.2
Teeth
Teeth (singular: tooth) are dense structures found in the jaws of
many vertebrates. They have various structures to allow them to
fulfill their different purposes. The primary function of teeth is to
tear, smell and chew food, while for carnivores it is also a weapon.
Therefore, teeth have to withstand a range of physical and chemical
processes, including compressive forces (up to ~700 N), abrasion
and chemical attack due to acidic foods or products of bacterial
metabolism [549]. The roots of teeth are covered by gums. From
the surface teeth are covered by enamel of up to ~2 mm thick at
the cutting edges of the teeth, which helps to prevent cavities on
the teeth. The biggest teeth of some gigantic animals (elephants,
hippopotamuses, walruses, mammoths, narwhals, etc.) are known
as tusks or ivory.
Similar to the various types of bones, there are various types of
teeth. The shape of the teeth is related to the animal's food, as well
as its evolutionary descent. For example, plants are 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. Thus,
the following types of teeth are known: molars (used for grinding up
food), carnassials (used for slicing food), premolars (small molars),
canines (used for tearing apart food) and incisors (used for cutting
food). While humans only have two sets of teeth, some animals have
many more: for example, sharks grow a new set of teeth every two
weeks. Some other animals grow just one set during the life, while
teeth of rodents grow and wear away continually through the animal
gnawing, maintaining constant length [676, 677].
Similar to bones, the inorganic part of teeth also consist of
biological apatite [678]. The stability of the mineral composition of
teeth also has a very long history: namely, calcium orthophosphates
were found in fossil fish teeth [679]. recent investigations of
biological apatite from fossil human and animal teeth revealed its
similarity to the modem biological apatite [680].
The structure of teeth appears to be even more complicated
than that of bones (see Fig. 1.13). Unlike bones, teeth consist of at
least two different materials: enamel, which is a hard outer layer
consisting of calcium orthophosphates, and dentine, which is a
bone-like magnesium-rich tissue that forms the bulk of vertebrate
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