Clinical study of stability of micro implant used as orthodontic anchorage

Objective:To study the stability of micro implant anchorage under orthodontic force.Method:Sixteen adult female patients with micro implants as the maxillary anchorage were included in this study.Micro implants were inserted on the maxillary alveolar between the second premolar and the first molar as a direct anchorage for anterior teeth retraction.Ni-Ti spring were placed between the micro implant and the hook on the basal archwire for the retraction 2 weeks after insertion of the micro implants.Cephalometric radiographs were taken immediately before force application and 9 months later.The cephalometric tracings were superimposed to determine any movement of the micro implants.Result:The micro implants were extruded and tipped forward(-1.0～1.5 mm) in 5 of the 16 patients.On average,the micro implants tipped forward significantly,by 0.4mm at the implants head.Conclusion:Micro implants are a stable anchorage but do not remain absolutely stationary throughout orthodontic loading.They might move according to the orthodontic loading in some patients.To prevent micro implants hitting any vital organs because of displacement,it is recommended that they be placed in a non-tooth-bearing area that has no major nerves or blood vessel pathways,or in a tooth-bearing area allowing 2mm of safety clearance between the micro implants and dental root.