Tooth

A tooth (pl.: teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and is used to break down food. Animals like carnivores and omnivores also use their teeth to catch prey, tear food, defend themselves, or show strength to others. The roots of teeth are covered by gums, and teeth are made from special tissues, not bone, that come from the outer layer of early development in animals.

Teeth look similar in many animals but can vary in shape and position. For example, mammals and some fish have teeth with deep roots, while fish called teleosts have teeth on the surface of their bones, and lizards have teeth attached to the inside of their jaws. Sharks have teeth held on by strong ligaments and can grow a new set every two weeks.

Some animals, called monophyodonts, only grow one set of teeth, while others, called diphyodonts, like most mammals including humans, grow two sets: baby teeth and adult teeth. There are also animals called polyphyodonts, such as sharks, elephants, and kangaroos, that can grow many sets of teeth throughout their lives. Rodents like beavers have special teeth called incisors that keep growing, which helps them chew wood. Some rodents and rabbits also have teeth that never stop growing.

Etymology

The word "tooth" comes from very old language roots. It started from a word that meant "that which eats."

The word "teeth," the plural of "tooth," changed shape over time due to language rules. This kind of change can be seen in other words too, like how "mouse" becomes "mice." The word for "tooth" also connects to words in other languages, such as the Latin word for tooth and the Greek word for tooth.

Origin

Teeth likely started from special scales on the skin of early fish, which moved into their mouths to help with eating. Scientists have found evidence in ancient fish fossils that show teeth and scales were made from similar materials. Some animals, like lizards and snakes, still have extra teeth in the roof of their mouths, but mammals, birds, and crocodiles do not.

Mammals

Main article: Mammal tooth

Teeth are very important and lasting features of mammals. Scientists called paleontologists study teeth to learn about ancient animals and how they are related to each other. The shape of an animal's teeth matches what it eats. For example, animals that eat plants, called herbivores, have many teeth for grinding food. Animals that eat meat, called carnivores, have sharp teeth for catching and tearing their food.

Most mammals, including humans, have two sets of teeth. The first set, called baby or primary teeth, starts to appear when babies are about six months old. This time is called teething and can be uncomfortable. Some animals, like kangaroos, elephants, and manatees, are different because they keep getting new teeth their whole lives.

Aardvark

Aardvarks have teeth without enamel that have many tiny tubes inside.

Canines

Dogs have teeth that don’t get cavities as easily as humans because their saliva is very high in pH, which protects their teeth. These pointed teeth, sometimes called cuspids, help dogs tear and grab food.

Cetaceans

Main article: Baleen

Whale teeth have special bumps on their roots. Toothed whales have many teeth, but narwhals have one giant tooth that looks like a tusk. This special tooth helps them sense their surroundings while feeding, navigating, and mating. Beaked whales usually have very few teeth, mostly found only in males.

Primates

Main articles: Human tooth and Dental anatomy

Humans and most primates have 20 baby teeth and later up to 32 adult teeth. Some adults have wisdom teeth, which are extra teeth at the back of the mouth that might need to be removed.

Horse

Main article: Horse teeth

An adult horse has between 36 and 44 teeth. Horses don’t have many canine teeth, and female horses usually don’t have any. Some horses have extra teeth called wolf teeth that are often removed because they can cause problems. By looking at a horse’s teeth, you can guess its age. Young horses have baby teeth that are replaced by adult teeth around age five. Older horses wear down their teeth, and very old horses might lose their teeth and need special food.

Proboscideans

Main article: Elephant ivory

Elephants use their tusks, which are special teeth, for digging up food and defending themselves. Elephant teeth are like plates and change throughout their lives. They start with 28 teeth at birth and slowly wear them down. When elephants lose their last teeth, they can’t chew food anymore and might not survive.

Rabbit

Rabbits are born with their permanent teeth and don’t have baby teeth. Their teeth grow continuously because they eat tough plants. Rabbits have six front teeth on the top and bottom, and their teeth wear down a little bit every week from chewing.

Rodents

Rodents have special front teeth that grow continuously and never stop. These teeth have enamel on the outside and wear down when rodents chew on things like wood or fruit. Some rodents also have teeth that keep growing at the back of their mouths.

Manatee

Manatees keep getting new teeth their whole lives. Their teeth develop separately from their jaws and are protected by bone.

Walrus

Main article: Walrus ivory

Walrus tusks are special teeth that grow continuously.

Fish

Fish, like sharks, can have many teeth during their lives. This constant replacement of teeth is called polyphyodontia.

Some ancient sharks are named cladodonts because of their unique split teeth. Unlike modern sharks, many early fish kept all their teeth throughout their lives. This is shown in the tooth arrangements of acanthodians, which include the oldest known fish with teeth, Qianodus duplicis.

See also: Pharyngeal teeth and Shark tooth

Amphibians

All amphibians have special teeth called pedicellate teeth. These teeth are flexible because of connective tissue and a part called dentine that separates the top from the base.

Most amphibians have teeth that attach slightly to their jaws or have acrodont teeth. These teeth don’t connect very strongly to the jaw and don’t need much energy to grow back. This works well for catching prey but isn’t good for crushing food. Teeth can be lost easily when catching struggling prey. Amphibians that change form as they grow develop bicuspid shaped teeth.

Reptiles

The teeth of reptiles keep getting replaced throughout their lives. For example, young crocodilian animals can replace their teeth very quickly—sometimes getting a new tooth in each spot every month. As they grow older, this process slows down, and it might take two years or more to get new teeth. Overall, crocodilians may use around 3,000 teeth from when they are born until they die. New teeth grow inside the old ones.

Birds

Main article: Ichthyornis

Scientists found a skull of Ichthyornis in 2014. This discovery helps us understand how birds' beaks might have developed from teeth. The change may have helped baby birds break free from their shells sooner, keeping them safe from danger and letting them reach food hidden under tough surfaces.

Invertebrates

True teeth are only found in vertebrates, but many invertebrates have similar structures often called teeth. For example, some parasites like hookworms have small cutting plates that act like teeth.

Leeches, which are also parasites, have sharp, saw-like jaws with about 100 teeth used to cut into their host's skin. Molluscs, such as snails and slugs, have a structure called a radula, which is a ribbon covered in tiny teeth made of chitin. The radula helps them scrape or cut food. Some sea snails use their radula to bore through the shells of other creatures, while others use it like a harpoon to catch prey. Limpets use their very strong radula teeth to scrape algae off rocks.

Fossilization and taphonomy

Teeth are very strong and often stay preserved when bones do not, making them important for scientists who study ancient life. They can tell us about the food that ancient animals ate. Early fish had hard parts in their bodies made of a material called dentine, which might have started as scales that moved into their mouths.

Even though teeth are tough, they can break. Scientists can learn about how strong the bite of ancient animals was by looking at these breaks. They can also find clues about the diet and behavior of these ancient creatures by studying how the tooth covering, called enamel, breaks apart. When enamel is removed, only the softer inside part of the tooth, called dentine, remains. Enamel can be worn away or lost before the rest of the tooth disappears during the process that turns bones into fossils. In such cases, what is left of the tooth is mainly the dentine, with an empty space where the soft center used to be. The soft part of dentine can be destroyed by certain chemicals.