Clinical Study Of Microimplant-aided Sliding Mechanics On Lower Arch Distalization In Three Dimensional Directions

Objective:To evaluate the effects on the lower arch distalization by microimplant-aided sliding mechanics, and analyse the mechanism of the dentition movement.Method:12patients with class Ⅲ malocclusion were treated by microimplant-aided sliding mechanics on lower arch distalization without extraction of the premolars or other teeth except the third molars. The microimplant was embedded in buccal shelf ’area between mandibular first and second molar.12patients were observed using CBCT and a three-dimensional reference frame was set up to compare the position and angle changes of lower arch. SPSS16.0software package was used for statistical analysis.Results:1. Changes in sagittal planeThe average amount of the distalization at the mesial buccal cusp, distolingual cusp and mesial root apical of mandibular first molar were3.09mm,2.60mm and1.37mm. The amount at the buccal cusp and lingual cusp of mandibular first premolar, the cusp of canine and the mesioincisal angle of central incisor was3.15mm,2.66mm,3.31mm and3.41mm. The average distal tipping angle of mandibular first molar, first premolar, canine and central incisor were5.04°,7.52°,8.32°and11.41°. 2. Changes in vertical planeThe mesiobuccal cusp of mandibular first molar, buccal and lingual cusp of first premolar showed extrusion by0.46mm,0.34mm and0.44mm. The distal lingual cusp of mandibular first molar showed intrusion by0.37mm. But they were not statistically significant. The cusp of canine and the mesioincisal angle of central incisor showed extrusion by1.17mm and1.57mm. At the same time, the mandibular occlusal plane showed counterclockwise rotation by2.93°, this was statistically significant.3. Changes in horizontal planeThe mesiobuccal and distolingual cusp of mandibular first molar were moved buccally by0.56mm and0.33mm with approximately1.62°of buccal tipping, which was statistically significant. The mandibular first molar and premolar show distal rotation by2.61°and5.37°.Conclusion:Significant true distalization of lower arch could be obtained by microimplant-aided sliding mechanics. Mandibular molar showed body movement and a certain degree tipping movement. Mandibular premolar, canine, incisors showed controllable tipping movement. At the same time, Mandibular occlusion plane contrarotated. Studies suggest that we must pay attention to the selection of archwire and size of the forces, the evaluation of the incisor root position in the alveolar bone and the control of lower teeth in three dimensional directions when lower arch was distalized, so as to achieve the tooth-face aesthetics, healthy periodontal, stable occlusion and function eventually.