Molar (tooth)

Molars are the rearmost and most complicated kind of tooth in most mammals. In many mammals they grind food, hence the name which means "millstone". Molars differ considerably from one species to another, so there are many terms describing them:

• Tribosphenic: This kind is found in insectivores and young platypuses (adults have no teeth). Upper molars look like three-pointed mountain ranges; lowers look like two peaks and a third off to the side.
• Quadrate: This kind is found in humans and various other species. Four cusps are arranged in a rectangle; there may be a fifth.
• Bunodont: The cusps, instead of being sharp peaks, are rounded hills.
• Hypsodont: There is a lot of enamel and dentine above the gumline and the top of the pulp. This kind of molar is found in mammals that wear their teeth a lot, such as the horse.
• Zalambdodont: The tooth has two ridges that meet at an angle, forming the letter lambda.
• Dilambdodont: Like zalambdodont, but there are two lambdas on one tooth.
• Lophodont: The tooth has a few ridges perpendicular to the jaw.
• Selenodont: The tooth has a crescent-shaped ridge or ridges.
• Loxodont: The tooth has several parallel oblique ridges on its surface. The elephant Loxodonta is named for this feature.

Adult humans have twelve molars, in four groups of three at the back of the mouth. The third (rearmost) molar in each group is called a wisdom tooth. It is the last tooth to appear, breaking through the surface of the gum at about the age of twenty.

For pictures of various molars see The Diversity of Cheek Teeth (http://animaldiversity.ummz.umich.edu/anat/tooth_diversity).