PRIMARY teeth also known as baby/milk teeth are 20 in number. They start appearing in the mouth at 4 months of age and by 3 years of age, all 20 teeth are present in the babies mouth.
Permanent dentition-it takes about 6 years (between 6-12 yrs of age) for the permanent teeth to replace the primary teeth. This phase of mixed dentition; one sees the presence of primary and permanent teeth in the mouth. Eventually, the 20 primary teeth are replaced by 32 permanent teeth.