Three-dimensional dental model analysis of treatment outcomes for protrusive maxillary dentition: comparison of headgear, miniscrew, and miniplate skeletal anchorage.

INTRODUCTION: The aim of this retrospective study on dental models was to compare the orthodontic outcomes of maxillary dentoalveolar protrusion treated with headgear, miniscrews, or miniplates for maximum anchorage.

METHODS: The 40 subjects were diagnosed as having either Angle Class II malocclusion or Class I bimaxillary dentoalveolar protrusion. All patients were treated to retract the maxillary dentoalveolar process by using the extraction space of the bilateral maxillary first premolars. They were divided into 3 groups according to the type of anchorage used. Group 1 (n = 16) received traditional anchorage preparation with a transpalatal arch and headgear, group 2 (n = 15) received miniscrews, and group 3 (n = 9) received miniplates for skeletal anchorage. To investigate the movement of the maxillary teeth during dentoalveolar retraction, we used a 3-dimensional (3D) digitizer to assess the positional changes of the maxillary teeth relative to the stable palatal rugose structures on the serial dental models. The 3D coordinates representing pretreatment and posttreatment maxillary dental casts were superimposed to determine the movement of individual teeth from the positional changes of 18 landmarks of the central incisor, canine, second premolar, and first molar.

RESULTS: Three-dimensional analysis of the maxillary dental models in the buccopalatal, anteroposterior, and vertical directions showed significant differences in tooth movements between the headgear and the mini-implant (miniscrew or miniplate) groups. Both skeletal anchorage groups had greater incisor retraction (6.9 mm for the miniscrew, 7.3 mm for the miniplate) than did the headgear group (5.5 mm). Mesialization of occlusal centroid of the maxillary molar in the skeletal anchorage groups was less than that in the headgear group (1.3 mm for the miniscrew, 1.4 mm for the miniplate, 2.5 mm for the headgear). Tooth movements in the anteroposterior and buccopalatal directions did not reach a statistically significant difference between the miniscrew and miniplate groups, but the maxillary posterior teeth of the subjects receiving miniplates showed greater intrusion than those receiving miniscrews anchorage.

CONCLUSIONS: This 3D analysis of serial dental models demonstrated that, compared with headgear, skeletal anchorage achieved better results in the treatment of maxillary dentoalveolar protrusion. Significant intrusion of the maxillary posterior teeth was noted in the miniplate group but not in the miniscrew and headgear groups. Greater retraction of the maxillary anterior teeth, less anchorage loss of the maxillary posterior teeth, and the possibility of maxillary molar intrusion all facilitated correction of the Class II malocclusion, especially for patients with a hyperdivergent face.