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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.
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