Development of teeth 

In humans, the first set (the baby, milk, primary  or deciduousteeth) normally starts to appear at about six months of age, although some babies are born with one or more visible teeth, known as neonatal teeth. In an embryo, tooth development begins after the 6th and 7th week, although the mouth structure begins to be appearing on 3rd week.

Eruption times

First tooth will erupt about 6 months old and the last wisdom teeth about 18-20. This means that the tooth development is about 20 years process. Milk tooth usually finishes their development by the age of 3.5 years old.

Permanent teeth will start growing around 6 yo. By age twelve there usually are only permanent teeth remaining. Nevertheless, there might be delays about 1-1½ years delay in the tooth development. 

Milk (deciduous) teeth

Normal tooth eruption at about six months is known as teething and can be painful. When complete they will be 10 in each row, in total 20. Milk incisors, canines and molars are smaller than the adult (permanent) teeth.  

The deciduous teeth will remain until the age of six. As the child grows, permanent teeth will start to develop. The erupting permanent teeth causes root resorption, where the permanent teeth push down on the roots of the deciduous teeth causing the roots to be dissolved and become absorbed by the forming permanent teeth. When the root of the deciduous teeth completely melt, and only the crown part left, it will fall off by itself.