Clinical effects associated with miniscrews used as orthodontic anchorage

To measure the clinical effects associated with miniscrew anchorage used to retract the upper anterior teeth, specifically the positional changes associated with the miniscrews, the upper anterior teeth and the first upper molars.

This clinical trial included 13 patients. After orthodontic alignment, miniscrews were inserted in the maxillary zygomatic buttresses as anchorage for en masse retraction of the upper anterior teeth. Following premolar extractions, nickel-titanium closed coil springs, stretched between the miniscrews and upper archwire, were used for retraction. Three-dimensional changes in the upper anterior teeth, the upper first molars and the heads of the miniscrews were measured on study models taken before a 300 g force was applied and seven months later, or when retraction was completed if less than seven months.

The mean duration of retraction was 5.23 months (SD: 1.74 months) with a range of three to seven months. The mean amount of anterior retraction was 3.82 +/- 1.64 mm (Range: 0.77-7.07 mm). Average movements of the miniscrew heads on the right side were 0.44 mm buccally, 0.38 mm forward and 0.54 mm downward, and on the left side 0.06 mm buccally, 0.41 mm forward and 0.50 mm downward. During the study period the right and left upper first molars moved mesially 0.70 +/- 0.46 mm (Range: 0.01-2.3 mm) and 0.76 +/- 0.47 mm (Range: 0.1-2.61 mm) respectively, although no force was applied to them.

Miniscrews provide satisfactory anchorage for retraction of the upper anterior segment, but do not remain absolutely stationary under orthodontic loads. Because of coincidental mesial movement of the upper molars, there must be sufficient clearance mesial to the molars to avoid the molar roots contacting the miniscrews.