The majority of 15-month-old babies should have 8 teeth, that is, 4 teeth in the upper jaw and 4 teeth in the lower jaw from the middle to the sides, all of which are the front teeth, all of which are incisors, which is the relatively normal tooth eruption for 15-month-old babies. The eruption of baby’s teeth starts just after 6-8 months of life and is completed between 2-3 years old, during which a total of 20 teeth should be erupted, the whole order of tooth eruption is first in the middle and then on both sides, the first to erupt is the lower jaw milk incisor, and then the upper jaw milk incisor, with the middle as the beginning to both sides.