Mandibular protrusion, that is, chin protruding forward. The pathogenic factors are heredity, trauma and disease. Most of them are related to heredity, some appear in childhood, and some appear in growth and development. Trauma, especially adolescent mental trauma, will cause indirect damage to condyle. Patients with severe mandibular protrusion are often accompanied by dentofacial deformities. There are also a few cases caused by scar twins after neck burns and acromegaly. Mandibular protrusion deformity is a common occlusion deformity, which has two types. One is coexisting with maxillary protrusion, but there may be jaw opening. One is caused by abnormal development of jaw or external branches. It is characterized by obvious protrusion of chin, and malocclusion may be accompanied by masticatory disorder. There are three common forms: front chin, lower chin and front chin. The correction of mandibular protrusion is the oldest in the correction of oral and maxillofacial deformities. At present, the most commonly used methods are vertical or oblique osteotomy of mandibular ramus and sagittal split osteotomy of mandibular ramus.