After the age of six or so, deciduous teeth – also known as baby or primary teeth – fall out and are replaced by the permanent teeth. According to the American Dental Association (ADA), baby teeth will start showing up in a child's mouth starting around the age of six months and continuing until he or she is about six years old. The baby teeth play an important role in helping a child learn to chew and speak, and they also serve as placeholders, saving the spot for the permanent teeth that will eventually erupt. Here are several differences between the deciduous and the permanent teeth.