To compare the clinical effects of the two methods of intruding overerupted molars by microscrews.

21 overerupted molars were selected and ramdomly divided into group A and group B. Group A was implanted with one microscrew anchorage at the side of the buccolingual tongue, and the force was produced by the tension spring. Group B was implanted with two microscrews combined with nickel - titanium fragments to lower the molars. The distances, velocities and microscrew anchorage failure rates were measured and compared between the two groups.

Two methods can achieve significant depressing effect, however, the failure rate of micro-screws was different in the two methods. The failure rates of group A and group B were 27.3% and 5.0%, respectively. The average speed of group A was 0.37 mm / month, and group B was 0.33 mm / month.

Both microscrew anchorage methods can effectively intrude overerupted upper molars. The speed of intrusion with microscrews directly is faster than NiTi Segmental arch and microscrews, but the implant failure of microscrews is higher.