Man has two sets of dentition in his life span. The first one is called DECIDUOUS dentition or MILK teeth or PRIMARY teeth. The second one is called PERMANENT dentition. The total no of milk teeth is 20 in number. 10 teeth in the upper arch and 10 teeth in the lower arch. The first milk tooth erupts into the oral cavity by around 6 months of age and by 3 years all 20 milk teeth would have erupted. There can be a variation of a few months in the eruption of these teeth.