Every individual develops two sets of teeth during the first 21 years of life. The first set begins to appear at approximately six months of age and are called primary teeth. They are often referred to as baby or milk teeth.
There are 20 primary teeth in the mouth. Normally, all twenty teeth erupt by the time a child is two years old. The first ones to erupt, at approximately six and a half months of age, are the lower central incisors. The last ones to appear are usually the upper second molars from 21 to 30 months. The eruption times of the individual teeth can vary considerably from one individual to another.
Once a child has all of their deciduous teeth, no visible changes in the teeth occur until around age six. At this time, the permanent molars begin to erupt.