Background  In clinical practice, there are some limitations in the routine treatment regimen for Angle class Ⅱ malocclusion with a good profile and Angle class Ⅰ malocclusion with mild crowding. The emergence of micro-implant anchorage provides a new idea for the treatment of these patients, and the use of micro-implant anchorage for distal movement of the entire maxillary dentition can expand the space well to solve the problems in such patients.

  Objective  To investigate the clinical effect of orthodontic micro-implant (OMI) anchorage for step-by-step distal movement of the maxillary dentition in the treatment of patients with Angle class Ⅱ division I malocclusion with a good profile and Angle class Ⅰ malocclusion with mild crowding, and observe the changes of maxillary teeth in the three-dimension direction, so as to provide guidance for micro-implant anchorage for step-by-step distal movement of the entire maxillary dentition.

  Methods  A total of 17 patients with Angle class Ⅱ division I malocclusion with a good profile and Angle class Ⅰ malocclusion with mild crowding, who were treated with OMI anchorage for step-by-step distal movement of the entire maxillary dentition in the department of orthodontics in our hospital from June 2017 to November 2020 were included, and three-dimensional oral scan models were established before and after surgery to observe the movement of facial axis (FA) point in the mesiodistal, buccolingual, and vertical directions.

  Results  There were 2 male and 15 female patients, with a mean age of 24.4 years. All maxillary teeth showed mesiodistal movement after surgery, among which the 13th tooth had the maximum movement of 2.174 ± 1.235 mm (P＜0.05), and the 21st tooth had the minimum palatal movement of 1.035 ± 0.729 mm (P＜0.05). All posterior teeth except the second molars had buccal movement, among which the first molars had relatively small buccal movement, the 16th tooth had the buccal movement of 0.667 ± 0.462 mm (P＜0.05), and the 26th tooth had the buccal movement of 0.642 ± 0.504 mm (P＜0.05). The first premolars had the greatest buccal movement, the 14th tooth had the buccal movement of 1.211 ± 0.641 mm (P＜0.05), and the 24th tooth had the buccal movement of 1.240 ± 1.078 mm (P＜0.05). There was an increase in the vertical distance of the FA point of anterior teeth; the 11th tooth had the largest increase in the vertical distance of FA point of 1.051 ± 0.490 mm (P＜0.05), and the FA point of the 21st tooth increased by 0.986 ± 0.551 mm after surgery (P＜0.05). All posterior teeth except the first molar had a relatively small vertical change of FA point.

  Conclusion  All maxillary teeth have mesiodistal movement after step-by-step distal movement of the entire maxillary dentition using micro-implant anchorage. All posterior teeth except the second molar have buccal movement, and the closer to the position of the traction hook, the larger the range of buccal movement. Micro-implant anchorage for step-by-step distal movement of the entire maxillary dentition helps to lower the anterior teeth vertically, and the posterior teeth have a small vertical change.