Abstract: Objective  To analyze the effect of implant screws in the buccal cortical region of the maxillary second molars on the distal movement of the molars. 
Methods  Eighty patients who declined tooth extraction and orthodontic treatment in outpatient department of our hospital were divided into the observation group(n=40) and control group(n=40) by random number table method. The observation group was treated with implant screws in the buccal cortical region of the maxillary second molars, and the control group was treated with implant screws between the roots of the maxillary second premolars and the first molars. The effects of distal movement of the molars were evaluated by the changes of lateral x-ray images of the head before and after orthodontics. 
Results  Before orthodonic treatment, there was no statistical significance in u1-x, U1-y, U6-x, U6′-y and U6′-y between the two groups(P>0.05). After treatment, the U6′-y and U6′-y of the control group were significantly reduced compared with those before orthodonic treatment, while the U1-y, U6′-y and U6′-y of the observation group were significantly reduced compared with those before orthodonic treatment, and the MTD was significantly lower than that of the control group(P＜0.05). In addition, the U1-y and U6′-y of the observation group were significantly lower than those of the control group(P＜0.05). The differences of U1-y, U6-x, U6′-y, U6′-y and MTD between the two groups were statistically significant(P＜0.05), while the differences of U1-x were not statistically significant(P＞0.05). Before orthodonic treatment, there was no statistical significance in the comparison of facial angle, nasolabial angle, upper lip protrusion and lower lip protrusion between the two groups(P＞0.05). After orthodonic treatment, the facial angle, nasolabial angle and upper lip protrusion of the two groups were significantly improved(P＜0.05), while the lower lip protrusion was not significantly changed(P＞0.05). However, the improvement of facial angle, nasolabial angle and upper lip protrusion of the observation group was significantly better than that of the control group(P＜0.05). 
Conclusion  Implanting of an implant screw between the maxillary second premolars and the roots of the first molars produced a significant distal oblique movement of the maxillary first molars, while the implanting of an implant screw in the buccal cortical region of the maxillary second molars produced a better distal movement of the molars. 

Key words: orthodontics, corrective, dental implants, molar