# Long-Term Stability of Class II Malocclusion Treated with Maximly Molar Distalization
## 2 Materials and Methods
### Measurements  
Three serial lateral cephalometric radiographs were obtained from each patient for evaluations at 3 different observation periods: pre-treatment (T1), after fixed orthodontic treatment following maxillary molar distalization (T2), and post-treatment long term (T3). Lateral cephalometric films obtained at T1, T2, and T3 were transferred to the Dolphin Imaging 11.8 Premium program (Dolphin Imaging & Management Solutions, Los Angeles, CA, USA) (Patterson Dental Supply, Inc., St. Paul, MN, USA), calibrated, and custom-analyzed (Figures 1 and 2).  
In this study, the horizontal reference plane (X plane), which makes a 7\({}^{\circ}\) angle clockwise from the sella point to the SN plane, was used according to [PERSON] et al. (2018) The plane (Y plane) drawn at an angle of 90\({}^{\circ}\) from the sella point to the X plane was used as the vertical reference plane (Figure 2). We preferred the \"corrected Sella-Nasion Plane\", which was described by [PERSON] et al. (2018), because the plane of the SN is least affected by growth and development-dependent changes and is reproducible when assigned.  
Figure 1: Cephalometric angular measurements: (1) SNA\({}^{\circ}\), sella–nasion–A point; (2) SNB\({}^{\circ}\), sella–nasion–B point; (3) ANB\({}^{\circ}\), A point–nasion–B point; (4) SN-MP\({}^{\circ}\), sella–nasion–mandibular plane; (5) SN-OP\({}^{\circ}\), sella–nasion–oclusal plane; (6) U1-PP\({}^{\circ}\), maxillary central incisor–palatal plane; (7) U6-PP\({}^{\circ}\), maxillary first molar–palatal plane.  
Figure 2: Cephalometric linear measurements: 7\({}^{\circ}\): Angle between SN plane and X plane; (8) U1-X (mm), distance from maxillary central incisor to X plane; (9) U1-Y (mm), distance from maxillary central incisor to Y plane; (10) U6-X (mm), distance from maxillary first molar to X plane; (11) U6-Y (mm), distance from maxillary first molar to Y plane.  
The midpoint of the line connecting the widest mesio-distal dimensions of the maxillary first molar tooth was used in the cephalometric measurements because the crown is least impacted by distal tipping [10; 24; 25; 26]. The incision edge was used as a landmark to evaluate the movement of the upper incisor. To evaluate changes in the tooth axis inclinations, the long axes were established by the line passing through the center point and function point of the molar tooth and the incisor tooth's incision edge and root apex [15; 17; 24]. The angle of the long axes of the teeth with the palatal plane was measured [17].  
The maxilla was superimposed on the ANS-PNS planes to evaluate the change in positions of the U6 and U1 (Figure 3) [16; 24; 1]. In this study, to evaluate the movements of the maxillary teeth, the palatal plane connecting the ANS and PNS points was used, and superimposition was performed by overlapping this plane locally from the ANS point.  
Orthodontic models were created by taking upper and lower jaw measurements from each individual at T1, T2, and T3. The overjet, overbite, arch length, irregularity index, right and left molar relationship (the horizontal distance between the tip of the mesio-buccal cusp of the upper first molar and the median sulcus of the lower first molar) were made in the model analysis (Figure 4) [19; 27; 28]. A digital caliper with a 0.01 mm precision was used to take the measurements.