| Objective:To investigate the change of the change of the occlusal plane, and the anterior and posterior teeth in vertical and horizontal dimensions when closing the space in sliding mechanics with miniscrew anchorage. From the research some implications are got for clinical practice.Methods:16 patients (2 males,14 females, mean pretreatment age of 20.64 years) were selected in the Department of Orthodontics, Hospital of Stomatology in the School of Medicine, Zhejiang University. All the cases were started from July in 2007 to March in 2009, on the basis of predefined selection criteria.32 self-tapping miniscrews (6 Aarhus Mini-Implants(?),26 Cibei Anchorage Screws) were implanted between the roots of the second bicuspid and the first molar in the maxilla. A force of approximately 150 to 200g was applied bilaterally for en masse retraction of the upper anterior teeth for space closure.Treatment effects were analyzed by taking lateral cephalograms at TO (before treatment), T1 (before initiation of retraction) and T2 (space closed for several months). All the tracings were performed using the cephalometric analysis program Winceph6.0. The change of the occlusal planes, mandibular planes, overbite and overjet, the horizontal, vertical, and angular positions of the upper central incisors and the first molars between T1 and T2 were evaluated. The changes of inclination and the distance of teeth movement were measured in relation to the different reference planes as follows:the anterior cranial base (SN plane), perpendicular line to SN plane through S, PP plane. The occlusal plane (∠OP-SN), mandibular plane (∠MP-SN), the inclination of the upper incisor (∠U1-SN) and the vertical positions of the upper incisors and the first molars(U1-PP, UR-PP, U6-PP), the horizontal positions (U1-Sv,UR-Sv, U6-Sv) were measured. The statistical analyses were performed by using the SPSS 15.0. A paired-samples t test was used to evaluate the treatment change.Superimposition of T1 and T2 cephalograms was traced on PP plane, centered on ANS. The change of the maxillary central insicors and the first molars and their movement pattern were showed. Results:None of the 32 miniscrews became loose. The average time between T1 and T2 was 6.88 months.It showed a greater mean change of the occlusal planes (∠OP-SN), from 22.10°to 26.10°(P<0.001) between T1 and T2. The mean degree of the mandibular planes (∠MP-SN) was increased by 0.66°(P>0.05). There was no significant differences. The mean overbite was deepened by 0.78mm (P<0.01). The overjet was not significantly different. The mean upper incisor angulation change was decreased by 11.47°(P<0.001); the greater average perpendicular distances change from the edges of the upper incisors to PP plane (Ul-PP) was observed (1.10mm, P<0.001). The distances from the most apical point to PP plane (UR-PP) had no difference. The smaller average perpendicular distances change from the edges of the upper incisors to Sv line (U1-Sv) was observed (4.45mm, P<0.001). The distances from the most apical point to Sv line (UR-Sv) had no difference. The maxillary molars showed a net intrusion (0.51mm, P<0.001) and little distal movement. The superimposition trace showed the upper central incisors had lingual crown tipping and the molars tipped distally.Conclusion:1) Miniscrews are efficient and stable for intraoral anchorage reinforcement;2) The clockwise alteration of the occlusal plane was discovered in retraction the maxillary anterior teeth using sliding mechanics with miniscrews;3) The upper central incisors had tipping movement and insufficient torque control;4) The upper first molars had little intrusion and distal tipping movement.
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