Objective : To explore the related factors for the unilateral flap and bilateral flap by changing the original operation plan in the extraction of maxillary impacted mesiodens. Methods : 81 patients with impacted mesiodens in the middle of the maxillary were retrospectively analyzed. The primary outcome variables were planned surgery (unilateral flap)and unplanned surgery (bilateral flap) . The secondary outcome variables consisted of operation time and postoperative swelling. The predictive variables were as follows:the differential value of the shortest distance from the supernumerary tooth to the labial and palatal bone plates , which was divided into≥1. 5 mm group and < 1. 5 mm group ; the ratio of the distance from the adjacent tooth apex to the nasal floor, compared to the length of the supernumerary teeth , was recorded as≥1 and < 1 . A statistical software SPSS 20 was used to complete the statistical analysis. Results : When the differential value was less than 1. 5 mm , the possibility of unplanned surgery increased , and the probability of planned surgery was 0. 085 times than that of unplanned surgery. With age growing each 1 ⁃year, the probability of planned surgery gradually decreased , HR = 0. 745. The postoperative swelling of the palatal approach was only 0. 374 times than that of the labial approach. With age increasing , the operation time increased gradually , B = 1. 213. The ratio of the distance from the adjacent tooth apex to the nasal floor to the length of the supernumerary teeth did not affect the change of the surgical plan during the operation. Conclusion The shortest distance difference between the supernumerary teeth and the labial and palatal bone plates can be used as a reference for the selection of surgical approach for the extraction of maxillary impacted mesiodens.