The mandibular third molar eruption is commonly divided into three phases: pre-eruptive phase, the process of developing at the bottom of mandibular ramus as well as moving forward; pre-functional eruptive phase, dental germ moving along the axis of tooth with mesial movement; functional eruptive phase, gingival emergence to the occlusal plane. The factors affecting eruption space were modeling resorption of the mandibular ramus, growth amount of the mandibular arch and alveolar bone, sagittal growth amount of mandibular body, etc.. And eruption angulation was another variable associated with retromolar space, the development of root, sagittal skeletal classification, etc.. As for the methods to evaluate eruption space and angulation of third molar, cephalometric radiograph, panoramic radiograph and cone beam CT were included. However, it is not clear whether premolar extraction orthodontic treatment can have effects on the mandibular third molar eruption. Other factors may influence the angulation and position of the mandibular third molar and that it is not possible to predict exactly.
