Text A. Eruption of Teeth
Humans develop two sets of teeth during their lives. The first set of teeth are deciduous teeth, 20 small teeth also known as baby teeth or milk teeth. Both baby and permanent teeth grow out of tooth buds that were laid down under gums fairly early in embryonic life(before birth).Babys first tooth usually erupts above the gum line when he is about 6 month of age. The first deciduous tooth to erupt is one of the incisors. An infant usually has his full set of 20 deciduous teeth by the time he is 2 or 2 ½ years old.
Deciduous teeth influence the mouth and face. When baby teeth are lost too early the permanent teeth underlying them may erupt in an unnatural position and form a crowded or otherwise irregular dental arch. Furthermore, the child needs a good set of deciduous teeth to chew his food properly and to preserve a proper bite (occlusion) between the upper and lower jaws. Many children suffer from some degree of malocclusion (faulty bite).
So, primary teeth are very important as they help permanent teeth to erupt in their normal positions. When a primary tooth is ready to fall out, its root begins to dissolve. This root has completely dissolved by the time the permanent tooth below is ready to erupt.
Children start losing baby teeth at about 6 years of age. The first adult teeth to erupt are permanent molars that come through at the back of the mouth, right after last milk molars. These four grinding teeth are extremely important for correct development of an adult dentition. They are called the key stone of a dental arch and will carry the main burden of chewing for many years. The eruption of permanent teeth starts around the age of 6. From then until the child becomes 12 years old all primary teeth loosen and fall out while permanent teeth come through in their place. Permanent teeth replace baby teeth in the mouth at the rate of about 4 a year for 6 or 7 years.
The last teeth to erupt are wisdom teeth or third molars, which are usually delayed until late teens or early twenties. These teeth often come in crooked or impacted against second molars and may have to be extracted.
A full set of adult or permanent teeth numbers 32: 8 on each side above and below, namely: 2 incisors,1 canine,2 premolars and 3 molars.
The adult human teeth show a morphology mainly differentiated by the shape of their upper surface (crown) and the number of tooth roots. Individual tooth morphology is associated with the purpose of each tooth type (cutting, shredding or grinding the food).
IX. Answer the following questions.
1. How many sets of teeth develop in humans?
2. What are they?
3. Which deciduous teeth are the first to arrive?
4. Why are deciduous teeth important for a child?
5. Do many children suffer from malocclusion?
6. How many teeth are there in a full set of deciduous teeth?
7. What happens with the childs teeth at the age of 6?
8. Are 6-year molars permanent teeth? Why are they very important?
9. At what rate do permanent teeth replace baby teeth in the mouth?
10. Which teeth are the last to erupt?
11. How many teeth are there in a full set of adult teeth?
X. Complete the sentences using words from the active vocabulary. The first letters are given to help you.
1. A human has two s...of teeth: d and p .
2. E of deciduous teeth starts at six month and is completed at two years.
3. After deciduous teeth I, they are lost and replaced by permanent teeth.
4. Wisdom teeth are often e if they come in c or i.
5. A lot of people suffer from some kind of m.
6. Sometimes permanent teeth may form a cda.
7. It is very important for the child to preserve pb.
8. The eruption of wisdom teeth is duntil 18-25 years.
9. Deciduous teeth are replaced by permanent ones at the r of about 4 a year.
10. The t b are laid down before birth.
