Page 248 - Ultimate Visual Dictionary (DK)

THE HUMAN BODY

Teeth DEVELOPMENT OF TEETH IN A FETUS

THE 20 PRIMARY TEETH (also called deciduous or baby
Fetal skull
teeth) usually begin to erupt when a baby is about six
months old. They start to be replaced by the permanent
teeth when the child is about six years old. By the age of
Primary teeth
20, most adults have a full set of 32 teeth although the
in maxilla
third molars (commonly called wisdom teeth) may never (upper jaw)
erupt. While teeth help people to speak clearly and give
shape to the face, their main function is the chewing of
food. Incisors and canines shear and tear the food into Primary teeth
pieces; premolars and molars crush and grind it further. in mandible
(lower jaw)
Although tooth enamel is the hardest substance in the
body, it tends to be eroded and destroyed by acid FETAL JAWS
produced in the mouth during the breakdown of food. By the sixth week of embryonic development areas of
thickening occur in each jaw; these areas give rise to
tooth buds. By the time the fetus is six months old,
enamel has formed on the tooth buds.
DEVELOPMENT OF JAW AND TEETH

Maxilla
(upper jaw)

Mandible
(lower jaw)

A NEWBORN BABY’S JAWS A FIVE-YEAR-OLD CHILD’S TEETH A NINE-YEAR-OLD CHILD’S TEETH AN ADULT’S TEETH
The primary teeth can be seen There is a full set of 20 erupted Most of the teeth are primary By the age of 20, the full set of
developing in the jaw bones; primary teeth; the permanent teeth but the permanent 32 permanent teeth (including
they begin to erupt around the teeth can be seen developing in incisors and first molars have the wisdom teeth) should be
age of six months. the upper and lower jaws. now emerged. in position.

THE PERMANENT TEETH

Molars Premolars Canines Incisors Canines Premolars Molars

UPPER

LOWER

3rd 2nd 1st 2nd 1st Lateral Central Lateral 1st 2nd 1st 2nd 3rd
(wisdom) (wisdom)

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