Late eruption of teeth, also known as late eruption of teeth, is a period of tooth eruption significantly later than the normal eruption period. A. Late eruption of milk teeth It is normal for the first tooth to erupt one year after birth. If the first tooth does not come out even after 1 week of age, or if all the milk teeth have not come out yet after 3 weeks of age, it is considered late eruption. Usually, late eruption or difficulty in eruption of all or most of the milk teeth is related to systemic factors, such as nutritional deficiency, low thyroid function and rickets. Parents should identify the causes and treat the symptoms to promote the eruption of milk teeth. The causes of late eruption of permanent teeth are: 1) lesion, premature loss or retention of milk teeth. The most common is the premature loss of maxillary incisors, the child is used to biting things with gums, and the local gums become very tough, so that the eruption of permanent teeth is obstructed. 2, multiple teeth, dental tumors or cysts obstruction of such conditions can only be detected and diagnosed through x-ray examination. 3, genetic factors are extremely rare. Treatment principles: 1, due to premature loss of milk teeth, tough gingival tissue obstructs the eruption of permanent teeth too late, it is necessary to remove the thickened gingival tissue to expose the teeth. 2. If the eruption of teeth is hindered by tumors, cysts or multiple teeth, tumor removal is required. 3.If it is caused by systemic diseases, treatment should be carried out for systemic diseases.