Evaluation of the stability of self-drilling mini-implants for maxillary anchorage under immediate loading

To evaluate the stability of self-drilling mini-implants used for immediate en masse retraction of all anterior teeth.

Six patients with 12 self-drilling mini-implants (diameter 1.6 mm, length 6.0 mm), which were placed on each side between the maxillary first molar and second premolar, were evaluated. The mini-implants were loaded immediately after placement with a force of 200 cN. Lateral cephalograms were taken upon loading (T1) and after 6 months of retraction (T2). All T1 and T2 radiographs were analyzed by localizing the anterior border of the mini-implant heads. Their vertical displacement was measured in millimeters to the Frankfort plane; the horizontal displacement was measured to a line perpendicular to the Frankfort plane registered at sella.

Analysis of variance revealed a significant difference for the horizontal (P<.05) but not for the vertical pre- and posttreatment position.

Mini-implants provide good anchorage for the retraction of teeth. However, the self-drilling mini-implants used in this study did not remain absolutely stationary like osseointegrated implants. With loading, they moved in the direction of the applied force, but their displacement had no clinical impact.