Understanding the normal cycle of your child’s teeth eruption and falling out will help you make sure that their dental health is right where it should be. Eruption refers to the tooth breaking through the gum line. In babies, the eruption is also called teething. The timing of tooth eruption is different from one child to another. We don’t usually think of a newborn as having teeth. The 20 “baby” or primary teeth are almost entirely formed at birth, hidden from our view in an infant’s jawbones. The primary or baby teeth gradually erupt during the first 2 ½ years of life.