It is a normal physiological phenomenon for infants to grow only one incisor at the beginning of the teething period. If it is beyond the teething period, it may be due to malnutrition or missing teeth. 1. Normal physiological phenomenon: Under normal circumstances, babies will have teeth erupt gradually from 6 months of life, and at the beginning of teething, there may be only one incisor, and then gradually grow a second one, which is a normal physiological phenomenon. 2. Malnutrition: If a tooth does not grow for more than half a year after it erupts, you should consider whether there is malnutrition, lack of vitamins, lack of trace elements and other reasons. 3. Missing Teeth: The missing teeth may be caused by the underdevelopment of milk teeth, which may also lead to the growth of only one incisor. If it is a physiological phenomenon, there is no need for treatment, but if there is a disease, you should go to the hospital for examination and treatment.