Most people have two sets of teeth (dentitions): primary (baby) teeth and permanent (adult) teeth. When a child has a mixture of primary and permanent teeth it is called mixed dentition.
Understanding the Sets of the Teeth
Primary Dentition (Ages 0-7)
This is the phase in which the child only has baby teeth. This phase starts with the eruption of the first tooth, usually a lower front tooth, and lasts until the first adult tooth erupts. Most children have all 20 baby teeth erupt by the age of 2 ½. The primary dentition lasts until 5- 7yrs old, depending on the patient. Generally, girls develop faster than boys. To help the dental staff communicate, in the United States baby teeth are named by letters A-T.
Mixed Dentition (Ages 5-13)
This is the phase of the teeth when the child has both baby and adult teeth. While the child is in the mixed dentition they will lose all of the baby teeth over 5-7 year period. During early mixed dentition the child has more baby teeth than adult teeth and during late mixed dentition the child has more adult teeth than baby teeth. During the majority of the mixed dentition the child will have 24 teeth (12 baby and 12 adult). Mixed dentition starts between the ages of 5-7 and lasts until the ages of 11-13. At this age the child will have some teeth named by letters (baby teeth) and some teeth named by numbers (adult teeth) to help with communication.
Adult Dentition (Ages 11+)
Once all the baby teeth have been lost the child moves into the Permanent Dentition (Adult Set of Teeth). This usually occurs between the ages of 11-13. At this point the child will only have teeth that are named by numbers 1-32.