Biomechanical mechanism of microimplant combined with traction hooks of different heights for overall distal upper dentition

Abstract Objective To investigate the biomechanical mechanism of microimplant combined with traction hooks of different heights for overall distal upper dentition in patients with maxillary protrusion without tooth extraction. Materials and methods Twenty patients (18–30 years old) with maxillary protrusion without tooth extraction participated in the study between March 2019 and May 2020 in the Department of Orthodontics, Shanxi Medical University. They were randomly divided into two groups. The microimplants were implanted in the maxilla between 15 and 16 and 25 and 26, about 10 mm from the archwire, and the traction hooks were between 12 and 13 and 22 and 23. Group A:the force line of the microimplant and the traction hook was below the center of resistance of the maxillary arch and the anterior teeth; Group B: the force of the microimplant and traction hook was close to the center of resistance of the anterior teeth. The lateral cephalic radiographs before and after treatment were measured and analyzed to determine the influence of the two groups on the depression of the upper posterior teeth, rotation of the occlusal plane, advancement of the chin, and the depth of the mental labial groove. Results The values of FH-OP, U1-PP, U6A-PP, U6D-PP, Ptm-U6D, LL-B'-Pog', and Pog'-G after treatment were significantly lower than those before treatment, and the value of B'-LLPog' increased significantly after treatment than that before treatment in Group A. The values of Ptm-U6D and B'-LLPog' after treatment in group B were significantly lower than those before treatment, while the value of LL-B'-Pog' after treatment was significantly higher than that before treatment; the other values were not statistically significant. Conclusion The anterior teeth were retracted with implants. When the force of the implant and traction hook was below the center of resistance of the maxillary arch and the anterior teeth, the occlusal plane was counterclockwise, the maxillary molars were tilted backward and moved backward, and the Mentolabial Sulcus was deepened, and the chin region could be moved forward.