Application Of Posterior Vertical Control Of High Angle Extraction Cases By Mircroscrew Implant Anchorage

Objective:To explore the clinical application of posterior vertical control of high angleextraction cases by mircroscrew implant anchorage.Method:18patients with high mandibular plane angle and class I or class II skeletalrelationships were selected for the current study. All of them had been treeted withextraction of four first premolars and MBT straight wire technique. To vertical controlthe posterior teeth, microscrews were implanted in the buccal alveolar bone betweenthe first and second molars and a transpalatal bar was placed to prevent the arch formand buccoversion of the posterior teeth during intruding force application. For theserious openbite case, microscrews were implanted in both of the buccal and palatalalveolar bone.Results:The treatments of all the high angle patients were successfully finished within22months and the soft tissue profile was significantly improved in the openbite patientswho had normal overjet and overbite relationships after the orthodontic treatment.Cephalometric analysis for treatment results showed that, for skeletal changes,MP/SN angle decreased by3.31°in average; MP/FH angle decreased by3.30°andY-axis angle decreased by8.07°in average; SNPo angle increased by2.12°inaverage. The mandibular plane was evidently counterclockwise rotated which movedthe chin forward and upward. In the dental changes, the upper molars were intrudedby2.12mm and the lower molars were intruded by1.47mm in average; U1-NAdecreased by3.13mm which indicated that the maxillary anterior teeth were retractednoticeably. The soft tissue changes included that NsPos/FH angle increased by3.36°in average and the anterosuperior movement of the chin cups was achieved; UL-SnPg’ decreased by1.86mm and LL-SnPg’ decreased by3.01mm in average that advocatedthe retraction of the anterior teeth in sagittal direction. The distance differencebetween the UL-SnPg’ and LL-SnPg’ increased by1.15mm in average that statedmore lower lip retraction than upper. Significant differences (P<0.001) were found inall the changes.Conclusion:The vertical control of the posterior teeth in the high angle cases is veryimportant. As the stable anchorage, the microscrew implant anchorage can intrude themolars, which resulted in the anterosuperior rotation of the mandible and reducing themandibular plane angle. All of these contributed to an improved facial profile and abetter smile. The location and the direction of the microscrew implant, the orthodonticforce and technique of the implantation should be taken into consideration so that theorthodontic treatment can achieve a satisfactory clinical outcome and meet thepatient’s expectations.