In the case of permanent teeth, the teeth next to the incisors are called lateral incisors; in the case of milk teeth, the teeth next to the incisors are called milk lateral incisors. There are two sets of teeth in a person’s life, one set of milk teeth and one set of permanent teeth. Milk teeth usually erupt at the age of 6 months and are completed at the age of 2.5 years, there are 20 teeth in total, 5 each symmetrically on the upper and lower sides, starting from the midline as milk mesial incisors, milk lateral incisors, milk cuspids, the first molar, and the second molar, respectively. Permanent teeth usually start erupting and replacing milk teeth at the age of 6, and are completed at about 13 years old, with a total of 28 teeth (except wisdom teeth), symmetrical on the top and bottom, 7 each, starting from the midline as mesial incisors, lateral incisors, cuspids, first premolars, second premolars, first molars, second molar, respectively. It should be noted that there are some patients with congenitally missing teeth as well as patients with congenital malformation of lateral incisors. It is recommended to have regular oral checkups and to seek prompt medical attention if there is any discomfort.