 Teeth have to be very hard to withstand all the chewing
and crunching of food. The hard material of the tooth is composed of
calcium, phosphorus, and other mineral salts. The material in the majority
of the tooth is called dentine. The
hard, shiny layer that you brush is called the enamel.
Teeth have two basic parts, a root to anchor the tooth to the jaw
and a crown above the gum line. The root is covered with a hard
material called cementum. At the center
of each tooth is an area with nerves, arteries and veins called the
dental pulp.
Humans have four different types of teeth, each with a different
function:
Incisors for cutting off bites of
food.
Cuspids (sometimes called
canines because of their long sharp points) for tearing food
Bicuspids (with two points) to tear
and crush food
Molars with large
relatively flat surfaces to crush and grind food.
Our four different types of teeth together are called collective
dentition and they allows humans to be
omnivores (eating both meat and
vegetables). Most animals have more specialized teeth. Carnivorous
(meat eating) animals have long sharp tearing teeth (like our
incisors and cuspids). Grazing animals,
like cows and horses have large flat teeth (like our molars) for
grinding grass and other vegetation. |
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note:
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phosphorus: 磷
mineral salt: 天然盐
dentine: 牙质
enamel: （牙齿的）釉质
cementum:
牙骨质
dental pulp: 牙髓
incisor: 门牙
cuspid: 犬齿
bicuspid: 两尖齿
molar: 臼齿
dentition: 齿系
omnivore: 不偏食的人
grazing animal: 食草动物 | |
