Objective To compare the effect of three kinds of extraction model on high angle bimaxillary protrusion patients. Methods A total of 30 patients with Class Ⅰ malocclusion and bimaxillary protrusion, aged 14-25 years old, were selected and divided into three groups. Four first premolars were extracted in the first group. The two maxillary first premolars and two mandibular first molars were extracted in the second group. The two maxillary first premolars and two mandibular first molars were extracted in the third group, and two additional micro-implants used as orthodontic anchorage in maxilla. Three groups were all treated with MBT appliance. Cephalometric analysis were carried out before and after treatment, and the results were analyzed with statistics. Results 1）About the hard tissues, compared with the first group, there were statistically significant differences of N-Me, SGo/NMe, ANS-Me, FH/ MP, SN/MP, and ODI in the second and the third group after treatment（P
