The tooth number and function

Number
The teeth as a whole describe two dental arches  in the shape of a horseshoe for each of the jaws. The lower dental arch based on the lower jaw or mandible, the other on the upper jaw or upper jaw. During our lives, two sets of teeth will appear in our mouth.
In the first, the baby teeth or teeth lacteal doing their eruption, and then followed by permanent teeth or definitive. Towards the age of three, all lacteal teeth (or teeth) are present in the mouth and in a few years, they will all be replaced by permanent teeth. 
The baby teeth are only 20. From the center of the mouth, there are on each side of each of the dental arches of a total of 10 teeth: 2 incisors (one central, the other side), 1 canine and 2 molars. Gradually, between 6 and 12 years, the teeth will all fall to give up their permanent teeth to 'grow' below. Thus, for arcade, 4 permanent incisors and canines 2 milk by 2 canines and 4 permanent molars milk by the 4 permanent premolars will replace the 4 incisors milk. The sequence of tooth eruption lacteal and follow the following schedule although there are individual variations. Around 6 - 8 months for the lower central incisors, 8-10 months for the upper central incisor and lower lateral incisors, 10-14 months for upper lateral incisors, 14-18 months for the first molars of upper and lower milk, 18 -24 Month for the upper and lower canine and 24-30 months for the second molar of upper and lower milk. The permanent molars, they will make their appearance without replacing any tooth. There are 6 by arcade. The first molar fate to the age of 6, the second around 12 years and the third, also called 'wisdom teeth' fate in adulthood.
Function teeth
Of course, teeth are useful and their main function is to enable us to chew food. But our teeth also have other roles: phonation and aestheticism.
Mastication
The special shape of each tooth has a direct influence on its function.
Thus, the incisors are used to cut food. The dog used to shred, while molars are used to grind food. The pre-molars have an intermediary role between canines and molars: they serve both to shred and grind.
Phonation
The teeth are used to support the lips and cheeks for a good speech.
The aesthetics
The shape and position of teeth determines the smile and teeth are used to support the lips and cheeks