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Tooth Structure and Development
- Enamel: The hard outer layer of the tooth that protects the underlying dentin.
- Dentin: A layer beneath the enamel that makes up the bulk of the tooth structure.
- Pulp: The soft tissue at the center of the tooth that contains blood vessels and nerves.
- Cementum: A layer that covers the root of the tooth and helps anchor it to the jawbone.
- Root: The part of the tooth that is embedded in the jawbone.
- Tooth development begins before birth.
- The first set of teeth, called primary or deciduous teeth, start to erupt around 6 months of age.
- Permanent teeth begin to replace primary teeth around the age of 6.
- The process of tooth eruption is regulated by a combination of genetic and environmental factors.
- Dental development can be influenced by nutrition and overall health.
Tooth Function
- Teeth play a crucial role in the process of digestion by breaking down food into smaller pieces.
- Different types of teeth have specialised functions for biting, tearing, grinding, and crushing food.
- Teeth also contribute to speech production by allowing the tongue and lips to form certain sounds.
- Healthy teeth and proper oral hygiene are important for maintaining overall health.
- Tooth loss or dental problems can affect a person's ability to eat, speak, and smile.
Tooth Evolution
- Teeth have evolved independently in different groups of animals, including mammals, reptiles, and fish.
- The structure and shape of teeth have adapted to the specific dietary needs of different species.
- Tooth evolution is influenced by factors such as diet, habitat, and natural selection.
- Fossil evidence provides insights into the evolution of teeth and the diversity of tooth forms.
- Comparative studies of tooth development and morphology contribute to our understanding of evolutionary relationships.
Types of Teeth
- Incisors: Used for cutting and biting food.
- Canines: Used for tearing and holding food.
- Premolars: Used for grinding and crushing food.
- Molars: Used for grinding and crushing food.
- Wisdom teeth: Third molars that often erupt in late adolescence or early adulthood.
Tooth in Different Animals
- Mammals: Teeth are a distinctive feature of mammal species and are used by paleontologists to identify fossil species. The shape of mammal teeth is related to their diet, with herbivores having many molars for chewing and grinding, and carnivores having canine teeth for killing prey and tearing meat. Most mammals develop two sets of teeth: a deciduous set and a permanent set.
- Horse: An adult horse has between 36 and 44 teeth. Horses have 12 premolars, 12 molars, and 12 incisors. Male horses usually have four canine teeth, while females have fewer and smaller canines. Some horses have one to four wolf teeth, which are often removed. Horse teeth can be used to estimate the animal's age.
- Proboscideans: Elephant tusks are specialised incisors for digging food and fighting. Elephants have 28 molar grinding teeth organised in sets. Only four teeth are used for chewing at a given time. The last and largest tooth usually becomes exposed around 40 years of age. When the last tooth falls out, the elephant can no longer chew food and will die of starvation.
- Rabbit: Rabbits shed their deciduous teeth before or shortly after birth. Rabbit teeth grow continuously throughout life. Rabbits have six incisors, three upper premolars, three upper molars, two lower premolars, and two lower molars on each side. The incisors and cheek teeth of rabbits are called aradicular hypsodont teeth. Rabbit incisors wear away about 3-4 millimeters every week.
- Rodents: Rodents have upper and lower hypselodont incisors that continuously grow enamel. Rodent incisors are used for cutting wood, biting through fruit skin, and defense. The enamel on rodent incisors has two layers: the inner portio interna with Hunter-Schreger bands and the outer portio externa with radial enamel. Rodent teeth self-sharpen during gnawing. Rodents lack canines and premolars, and have a space between their incisors and molars.
- Cetaceans: Whale teeth have polyp-like protrusions made of cementum, with the nodule located on the inside of the pulp chamber. The roots of human teeth are made of cementum on the outer surface, while whales have cementum on the entire surface with a small layer of enamel at the tip. Toothed whales have different types of teeth, ranging from numerous teeth in dolphins to a single unicorn-like tusk in narwhals. The narwhal tusk is the most neurologically complex tooth known and is used for sensing during feeding, navigation, and mating. Beaked whales are almost toothless, with only bizarre teeth found in males, which may be used for feeding and aggression.
- Manatee: Manatees have polyphyodont teeth. Mandibular molars develop separately from the jaw and are encased in a bony shell. Manatee teeth are separated by soft tissue. Manatees continuously replace their teeth throughout life. The dental structure of manatees is adapted to their herbivorous diet.
- Walrus: Walrus tusks are canine teeth that grow continuously. Walrus tusks are used for various purposes, including defense and foraging. The continuous growth of walrus tusks allows them to maintain their functionality. Walrus tusks can reach impressive lengths. The ivory from walrus tusks is highly valued.
- Reptiles: Reptiles constantly replace their teeth throughout their lives. Crocodilian juveniles can replace teeth at a rate of one new tooth per socket every month. Tooth replacement rates in mature crocodilians can slow to two years or longer. Crocodilians may use up to 3,000 teeth from birth to death. New teeth are formed within old teeth.
- Birds: The beak of birds may have evolved from teeth
A tooth (pl.: teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tearing food, for defensive purposes, to intimidate other animals often including their own, or to carry prey or their young. The roots of teeth are covered by gums. Teeth are not made of bone, but rather of multiple tissues of varying density and hardness that originate from the outermost embryonic germ layer, the ectoderm.
| Tooth | |
|---|---|
 A chimpanzee displaying his teeth | |
| Details | |
| Identifiers | |
| Latin | dens |
| MeSH | D014070 |
| TA98 | A05.1.03.001 |
| TA2 | 914 |
| FMA | 12516 |
| Anatomical terminology | |
The general structure of teeth is similar across the vertebrates, although there is considerable variation in their form and position. The teeth of mammals have deep roots, and this pattern is also found in some fish, and in crocodilians. In most teleost fish, however, the teeth are attached to the outer surface of the bone, while in lizards they are attached to the inner surface of the jaw by one side. In cartilaginous fish, such as sharks, the teeth are attached by tough ligaments to the hoops of cartilage that form the jaw.
Monophyodonts are animals that develop only one set of teeth, while diphyodonts grow an early set of deciduous teeth and a later set of permanent or "adult" teeth. Polyphyodonts grow many sets of teeth. For example, sharks, grow a new set of teeth every two weeks to replace worn teeth. Most extant mammals including humans are diphyodonts, but there are exceptions including elephants, kangaroos, and manatees, all of which are polyphyodonts.
Rodent incisors grow and wear away continually through gnawing, which helps maintain relatively constant length. The industry of the beaver is due in part to this qualification. Some rodents, such as voles and guinea pigs (but not mice), as well as lagomorpha (rabbits, hares and pikas), have continuously growing molars in addition to incisors. Also, tusks (in tusked mammals) grow almost throughout life.
Teeth are not always attached to the jaw, as they are in mammals. In many reptiles and fish, teeth are attached to the palate or to the floor of the mouth, forming additional rows inside those on the jaws proper. Some teleosts even have teeth in the pharynx. While not true teeth in the usual sense, the dermal denticles of sharks are almost identical in structure and are likely to have the same evolutionary origin. Indeed, teeth appear to have first evolved in sharks, and are not found in the more primitive jawless fish – while lampreys do have tooth-like structures on the tongue, these are in fact, composed of keratin, not of dentine or enamel, and bear no relationship to true teeth. Though "modern" teeth-like structures with dentine and enamel have been found in late conodonts, they are now supposed to have evolved independently of later vertebrates' teeth.
Living amphibians typically have small teeth, or none at all, since they commonly feed only on soft foods. In reptiles, teeth are generally simple and conical in shape, although there is some variation between species, most notably the venom-injecting fangs of snakes. The pattern of incisors, canines, premolars and molars is found only in mammals, and to varying extents, in their evolutionary ancestors. The numbers of these types of teeth vary greatly between species; zoologists use a standardised dental formula to describe the precise pattern in any given group.
