Effects Of Mini-implant Assisted Rapid Maxillary Expansion Combined With Class Ⅲ Elastic Traction In The Treatment Of Skeletal Class Ⅲ Malocclusion In Children

Objective:To evaluate and analyze the changes of skeletal surface and upper airway in patients with skeletal Class Ⅲ malocclusion who received mini-implants assisted rapid maxillary expansion combined with Class Ⅲ elastic traction by CBCT and cephalometric film before and after the treatment.The changes of maxilla and mandible position in sagittal and vertical direction and the volume,cross-sectional area,transverse diameter and sagittal diameter of upper airway were observed and evaluated after the treatment.Material and Methods:In this retrospective study,we collected skeletal Class Ⅲmalocclusion patients with skeletal age of CS1-CS2 from the Department of Orthodontics,Stomatological Hospital of Shandong University,and divided them into two groups:one group was treated with mini-implants assisted rapid maxillary expansion combined with Class Ⅲ elastic traction including 21 patients(Group A);the other group was treated with simple mini-implants assisted rapid maxillary expansion including 11 patients(Group B).The interval before and after treatment was more than 7 months.The cephalometric film and CBCT were taken before and after treatment for evaluation.We imported CBCT data into dolphin imaging software to analyze the changes of upper airway.We used SPSS software to analyze the data including the comparison and change value before and after the treatment.Results:We found that mini-implants assisted rapid maxillary expansion combined with Class Ⅲ elastic traction had obvious effects in promoting maxillary advancement and airway opening compared with simple mini-implants assisted rapid maxillary expansion1.In the sagittal comparison of maxilla,we found that the amount of maxillary advancement in Group A was significantly greater compared with Group B(P<0.05).In the comparison of both groups before and after the treatment,point A,point ANS and point PNS increased significantly(Group A:point A moved forward 2.08±1.10 mm,point ANS moved forward 2.12±1.41 mm,point PNS moved forward 1.47±1.19 mm;Group B,point A moved forward 0.93±0.75mm,point ANS moved forward 0.84±0.77mm,point PNS moved forward 0.75±0.46mm).By comparing the change values between Group A and Group B,we found that the change values of Group A at point A and point ANS were significantly greater compared with Group B2.In the vertical comparison of the maxilla,we found that the point A and point PNS of Group A and Group B moved down significantly(In Group A,point A moved down 1.01±1.54 mm,point PNS moved down 1.36±0.63mm;in Group B,point A moved down 1.60±1.18mm,point PNS moved down 1.32±0.41mm.However,the downward movement of point ANS only occurred in Group B and the amount was 1.42±1.16mm.No significant downward movement of point ANS was found in Group A.3.In the changes of the maxillomandibular relationship,we found that only the Wits value of Group A increased significantly before and after the treatment.Comparing the changes of Wits value of both groups,we found that the increase of Wits value of Group A was significantly greater than that of Group B.(Wits value increased by 3.05±2.05 mm in Group A and 0.38±2.02 mm in Group B)4.The volume of nasopharyngeal airway increased significantly in both groups.The volume of Group A increased by 1002.99±820.79mm3 and that of Group B increased by 995.78±701.52mm3.However,in the changes of velopharynx,glossopharynx and hypopharynx,the volume increased only in Group A(P<0.05),and the increase was 915.71±607.77mm3,1030.81±304.13mm3,1489.85±1256.64mm3 respectively.5.Comparing the changes of airway volume between both groups,we found that the increase of glossopharyngeal volume in Group A was higher than the increase in Group B.(P<0.05)Conclusion:Mini-implants assisted rapid maxillary expansion combined with ClassⅢ elastic traction has favorable effects in the early intervention of skeletal Class Ⅲmalocclusion,it can promote maxillary advancement without obvious clockwise rotation of mandible and compensatory mechanism of upper and lower anterior teeth.In addition,it can promote the opening of upper airway and improve respiratory physiology.