Comparison of the loading behavior of self-drilling and predrilled miniscrews throughout orthodontic loading.

INTRODUCTION: A predrilled miniscrew, when used as a temporary anchorage device in the infrazygomatic crest of the maxilla, can be displaced under orthodontic loading. The purpose of this retrospective cephalometric study was to compare the loading behavior of predrilled and self-drilling miniscrews placed in the infrazygomatic crest of the maxilla.

METHODS: The subjects were 32 women who had miniscrews in the infrazygomatic crest of the maxilla as skeletal anchorage for en-masse anterior retraction and intrusion; 16 had predrilled miniscrews, and 16 had the self-drilling type. The miniscrews were all 2 mm in diameter and 10 to 17 mm long. They were loaded with nickel-titanium closed-coil springs 2 weeks after placement. All the miniscrews remained stable, without detectable mobility or loosening, throughout the treatment period. Cephalometric radiographs were taken immediately before force application (T1) and at least 5 months later (T2). The T1 and T2 cephalometric tracings were superimposed to determine whether any displacement of the miniscrews had occurred.

RESULTS: The predrilled and self-drilling miniscrews were all significantly displaced in accordance with the force direction of the nickel-titanium coil springs. The amounts of miniscrew displacement were similar between the predrilled and self-drilling miniscrews, and were correlated to the length of the loading period. The displacements were 0.0 to 1.6 mm with extrusion, 1.5 mm with forward or backward tipping at the screw tail, and 1.5 mm with forward tipping at the screw head.

CONCLUSIONS: The loading behaviors of predrilled and self-drilling miniscrews were similar in the infrazygomatic crest of the maxilla. These miniscrews were all subject to displacement under orthodontic loading, and the amount of the displacement was correlated to the length of the loading period, although they remained stable without detectable mobility or loosening.