Comparison of Movement of the Upper Dentition According to Anchorage Method: Orthodontic Mini-Implant versus Conventional Anchorage Reinforcement in Class I Malocclusion

Objective. To compare the amounts of anchorage loss in the upper first molar (U6) and of retraction of the upper central incisor (U1) in cases with Class I malocclusion between orthodontic mini-implants (OMIs) and conventional anchorage reinforcements (CARs). Methods. The subjects were 40 female adult patients with Class I malocclusion who were treated with extraction of the first premolars and sliding mechanics. The subjects were divided into Groups 1 (N = 20, CAR) and 2 (N = 20, OMI) according to anchorage method. Lateral cephalograms were taken before (T0) and after treatment (T1). Seven skeletal and dental variables and ten anchorage variables were measured. Mann-Whitney test was used for statistical analysis. Results. Group 2 showed significantly larger retraction of U1 (U1E-sag, 9.5 mm : 7.1 mm, P < .05) and less anchorage loss of U6 (U6M-sag, 0.2 mm : 2.2 mm, P < .05; U6A-sag, 0.3 mm versus 2.4 mm, P < .01) than Group 1. There was opposite vertical movement in U1 and U6 between Groups 1 and 2 (U1E-ver, 0.9 mm intrusion : 0.7 mm extrusion; U6F-ver, 1.0 mm intrusion : 0.9 mm extrusion, P < .05). Conclusion. Although OMI could not reduce the treatment duration, it could provide better maximum anchorage of U6, greater retraction of U1, intrusion of U1 and U6 than CAR.