[Impact of maxillary sinus floor on the mesial movement of maxillary first molar].

To investigate the impact of maxillary sinus floor on the mesial movement of maxillary first molar.Orthodontic patients with maxillary first premolars extracted were selected. Their maxillary first molars were divided into case group and control group according to whether their roots were in contact with the maxillary sinus floor. The case group was further divided into three subtypes according to the depth of the root extruded into the maxillary sinus. A total of 64 maxillary first molars from 32 patients were enrolled in this study, including 34 in the case group (five in subtype Ⅱ, fourteen in subtype Ⅲ, and 15 in subtype Ⅳ) and 30 in the control group. The mesial movement distance of each root and crown and the inclination of each root long axis were measured, and resorption of each root was evaluated. SPSS 22.0 software package was used for data analysis.After orthodontic treatment, the mesial movement distance of roots from both groups were all lager than 2 mm. The mesial movement distance of the crown was not statistically different between the two groups (P＞0.05), while the mesial movement distance of the roots in the control group was significantly larger than in the case group（P＜0.05）. Inclined movement towards the mesial direction was found in both groups, and the inclination angle was significantly larger in the case group（P＜0.05）. The inclination angle of the first molars in the subtype Ⅳ was significantly larger than that in the subtype Ⅲ and the control group. Most of the maxillary first molars from both groups had no obvious root resorption（P＞0.05）.With the proper force system, maxillary first molars with roots extruded into the maxillary sinus floor can be moved mesialy with mild or no root resorption, while a larger inclination can be found compared with maxillary first molars without root extruding into the maxillary sinus floor. The deeper the root extruding into the maxillary sinus, the larger the inclination angle will be.