When a child’s front teeth don’t fall out and grow back, it is usually caused by retained milk teeth. The common causes of retained milk teeth are: over-nutrition, too fine food, insufficient development of the length of the dental arch. 1. Excessive nutrition: Nowadays, people’s living standard is generally improved, parents pay attention to children’s growth and development, often give children to eat fish, meat and other high-protein, high-fat food, children’s nutrition is excessive, affecting the root of the milk teeth can not be naturally absorbed. 2. Food is too fine: the development of science and technology, a variety of machines, such as wall-breakers, juicers, peelers, etc., instead of the teeth to chew the fiber of the food function, and the teeth only after and rough, chewy food grinding, chewing, in order to make the root of the milk teeth teeth loose, and conducive to the shedding of the teeth. 3. Insufficient development of the length of the dental arch: the eruption of the permanent teeth is too large, resulting in abnormal direction of the eruption of the permanent teeth, appearing in front of the teeth did not fall out of the back and then grow out of the situation. When children have double rows of teeth, parents should take their children to the hospital dentist in time to give the extraction of milk teeth to improve the symptoms of double rows of teeth.