The reasons why children’s teeth grow two layers are as follows: 1, physiological phenomenon: after the eruption of multiple teeth on the buccal and lingual side of the original teeth, the phenomenon of double rows of teeth can be presented. 2, inadequate jaw bone development: when the milk and permanent teeth begin to replace, due to inadequate jaw bone development, there is a difference between the width of the crown of the milk teeth and the crown of the permanent teeth, which will make the permanent teeth temporarily located on the lingual side of the milk teeth, forming a double layer of teeth. 3, the diet is soft: children like to eat When the permanent teeth are exposed to the oral mucosa, the milk teeth are not loosened, thus forming a double row of teeth. 4.Poor oral hygiene: The child’s oral hygiene is poor, and when deep caries occurs in the milk teeth and causes periapical inflammation, it will form adhesions with the surrounding tissues, causing the permanent teeth to erupt in the wrong position.