Childrens Illustrated Encyclopedia

515

HealtHy teetH

It is important to take care

of your teeth to keep them

healthy. teeth should be

cleaned with a toothbrush

and toothpaste at least twice

a day. Dental floss should

be used regularly. Sugary

foods are damaging to teeth

and cause tooth decay.

J awS

the upper jaw is fixed to the skull and

does not move. Powerful muscles in the

cheeks and the side of the head pull the

lower jaw up toward the upper jaw, so

that the teeth come together with great

pressure for biting. Other muscles pull

the lower jaw sideways, so that we can

chew with both up-down and side-to-side

movements. teeth are an important first

step in the process of digesting food.

Nerve

Dentine

Milk teeth and

adult teeth

Children have 20 milk teeth

that gradually fall out and are

replaced by a second set of

permanent adult teeth.

adults have 32 teeth in total.

each jaw has four incisors,

two canines, four premolars,

and six molars (two of which

are wisdom teeth). wisdom

teeth grow when a person is

about 20, although some

never push through the gum.

Temporalis

muscle pulls

jaw up.

Part of tooth

shows below

the gum line.

DentIStS

Dentists use x-rays (right) to see

the roots of teeth and to identify

any cavities. In the past, dentists

extracted decaying teeth, but now

only the affected parts are removed

and the hole is filled with hard artificial

materials. the white areas on this x-ray

are fillings and two crowns on posts.

Jawbone

Wisdom

tooth

Incisor

Premolar

Molar

Cementum

Root

eVeRy tIMe we eat we use our teeth to bite, chew, crunch, and grind

food. teeth enable us to break up food into small pieces so that our bodies

can digest it and use it. a tooth has three main parts—the crown of the

tooth, which shows above the gum; the neck, which shows at gum level;

and the root, which is hidden in the jawbone. the root of the tooth is fixed

securely in the jaw by a substance called cementum. a tooth has three

layers—creamy white enamel on the outside

(the hardest substance in the body); a layer of

dentine beneath; and the pulp cavity in the

center. the pulp contains many nerves, which

connect to the jawbone. there are four main

kinds of teeth; each kind is shaped for a

different job. Chisel-like incisors at the front

of the mouth cut and slice food; longer,

pointed canines tear and rip food; and flat,

broad premolars and molars crush and

grind it. During our lives, we have two

sets of teeth—milk teeth as children

and a second set of teeth as adults.

StRuCtuRe Of a tOOtH

teeth have one, two (like this molar),

three, or occasionally four roots, which

anchor them securely in the jawbone

and withstand the pressure of biting and 

chewing. Blood vessels that carry

nutrients and oxygen, and nerves that

transmit sensation, pass out through tiny

holes in the base of each root.

tuSkS

animals use

their teeth for

more than just

eating food.

large teeth help

defend an animal

against its enemies or

when fighting rivals during the

mating season. the tusks of

the warthog shown here are

huge canine teeth—like the

tusks of a walrus. tusks are used

to frighten off predators and,

sometimes, to dig up food.

Teeth

Cross section

of a molar

A set of

adult teeth

Find out more

Digestion

Human body

Canine Skeletons

Blood

vessels

Enamel

Gum

Lateral

pterygoid

muscles move

jaw from side

to side.

Pulp cavity

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