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.
