The Smilodon was smiling down, his teeth were bright and shiny,
young Mastodon ran to his mum and trumpeted 'corr blimey'.
That tiger guy's sure got big teeth, I hope he doesn't bit me.
He might like to try. His mother said, but while I'm here he never will.
'Cause though his teeth are mighty big mine are bigger still.
Teeth are important things, without them eating becomes a lot more difficult.
In mammals teeth have reached their highest peak of evolution, mammalian teeth are both more complicated and more efficient than in other vertebrates.
Teeth are heavy and require considerable muscle to operate efficiently, this has made an important contribution to the evolution of the mammal skull.
Teeth, like bones, are living structures. They rest in a specially designed cavity in the bones of the jaw and at least while they are growing they have a supply of blood and nutrients to them through their base. The crown is the outside of the part of the tooth that is above the jaw bone, it is the part that does all the hard work. It is capped with an extra hard substance called enamel. The rest of the tooth is softer, but still harder than bone. Beneath the enamel, making up the bulk of the tooth is the Dentine and within the centre is the pulp cavity. Enamel is 96% mineral while the dentine is 70% mineral. Teeth are seated in the jawbones and held in place by a special cement which is another form of bone. In the bottom of the tooth is a channel leading between the pulp cavity and the jaw bone which allows blood vessels to access the tooth. Most teeth stop growing once they reach a adult size and the cavity in the bottom of the tooth seals up, but some teeth like the incisors of rodents or the molars of sheep keep growing as they are worn down.
Teeth can be divided into two sections. The part above the gum called the crown and the part embedded in the gum called the root.
Teeth in mammals come in four different sorts: Incisors, Canines, Premolars and Molars. Not all mammals have all, or even any of them and the roles any particular sort of teeth play in an animal's life can be quite diverse. The arrangement of teeth in any given mammals mouth can be expressed as a 'dental formula'. This formula gives the arrangement of one side of an animal's jaw such that incisors are always written first then canines then premolars and then molars.
For humans 2123-2123 is upper and lower jaws respectively signifying 2 incisors, 1 canine, 2 premolars and 3 molars on each side in both the upper and lower jaw.
In total this adds up to 8 incisors, 4 canines, 8 premolars and 12 molars = 32 teeth in humans. Other mammals have different numbers of each sort of teeth in their upper and lower jaws. Hence Smoky Bats (family Furipteridae) have the dental formula 2123-3133 whilst Hyenas have 3141-3131 normally.
Incisors = Cutting teeth - these are the front most teeth in the jaw primarily used for the initial biting of food. They have a straight, sharp cutting edge and one root. In many Rodents they grow continually throughout the animals life, this is because they get warn down gnawing through things.
Canines = Stabbing teeth - normally only 2 pairs (one each side) per jaw. They have a sharp, pointed edge and are used with the incisors to bite into food and or to kill prey. Like incisors they have one root. The tusks of many animals such as elephants are modified canines. They are missing in rodents and most large herbivores (Perissodactyls and Artiodactyls). The gap where the canines would have been is often enlarged and is called a 'diastema'.
Premolars = Next back from the canines. They are generally similar to molars in form and function in both herbivores and omnivores, but in carnivores some of them at least are slimmer and are used to cut flesh. When they (the first lower premolar and last upper premolar) are modified like this they are called the carnassials. Otherwise premolars are teeth we use to crush and grind our food. Their upper surfaces have a broad, lumpy top instead of a sharp biting edge. These small irregular lumps are called cusps. Premolars are called bicuspids in some books, this is because, in most cases, they have two cusps. The prefix bi meaning two. The first upper premolars normally have two roots. The other premolars have one root.
Molars = These are larger than premolars and extremely variable depending on the animal's diet. Like premolars they are used for crushing and grinding food, and like premolars their upper surfaces have ridges called cusps on them. Molars normally have three to five cusps and two or three roots. In humans we call the third molars, those closest to the back of the mouth 'Wisdom Teeth'. If the jaw bone is not large enough to accommodate all the teeth in it, as sometimes happens with humans, these wisdom teeth can become painfully wedged between the back of the jaw bone and the 2nd molars. This condition is known as 'impacted wisdom teeth'.