People have two sets of teeth in their lifetime, one set of milk teeth and one set of permanent teeth. Milk teeth usually start to erupt around 6 months of age. It is normal for teeth to erupt at around 4 months of age or at 1 year of age. Usually the bottom teeth erupt before the top teeth, with the left and right teeth erupting at the same time, and all the milk teeth erupting by about 2.5 years of age. There are 20 baby teeth, 10 on the top and 10 on the bottom. You should take your baby to the hospital for a checkup if any of the following conditions occur: a. teeth have already erupted in the baby’s mouth at birth; b. teeth have erupted within 30 days of birth; c. none of the baby’s milk teeth have erupted beyond 12 months of age.