The causes of double-layered teeth in children include the following: 1. When multiple teeth erupt on the labial and lingual side of the milk teeth, a double-layered tooth row can be formed. The crowns of multiple teeth are usually tapered or irregularly shaped with curved roots, which can be directly extracted. 2. When permanent teeth erupt on the lingual side of the milk front teeth, a temporary double row of teeth can appear due to incomplete root resorption and inconspicuous loosening of the milk teeth. After the roots of the milk teeth are completely absorbed gradually, they will fall out by themselves.3. When chronic periapical infection occurs in the milk teeth, bacteria continuously destroy the alveolar bone and cause soft and hard tissue adhesions, resulting in the milk teeth remaining in the tooth row for a long time. Inherited permanent teeth can only grow towards the labial or lingual side, so the retained baby teeth can be extracted as soon as possible.