A three-dimensional evaluation of Class II subdivision malocclusion correction using Cartesian coordinates

Our objective was to evaluate the reliability of a comprehensive 3-dimensional (3D) evaluation method of dento-skeletal changes using Cartesian coordinates. The coordinates were used to evaluate changes that occurred during non-extraction orthodontic treatment of Class II subdivision malocclusions, and more specifically, describe how the Class II side was corrected to a Class I relation while maintaining the Class I side. The sample consisted of 25 adolescent orthodontic patients diagnosed with a Class II subdivision, and treated non-extraction to a bilateral Class I relation. The pre- (T1) and post-treatment (T2) Cone Beam Computed Tomography scans were oriented using the cranial nerve canals to set the 3 planes of reference, and 19 landmarks were registered on maxillary, mandibular, and dental structures. The data consisted of 3D coordinates representing the distances to the reference planes. A Class I side along with a Class II side was made for each subject. Comparisons were made between sides and between T1 and T2. The data was analyzed using t-test and Pearson׳s Correlation, and the intra-observer reliability was tested by intraclass correlation coefficient. The vertical dimension showed the most variability, both between patients and when comparing T1 versus T2. Treatment effects on the maxillary and mandibular molars on the Class II side were significantly different than the effects seen on the Class I side. There was a weak association between the transverse change, mandibular midline and the antero-posterior change of the mandibular molar on the Class II side. Gonion and PNS showed a tendency for posterior displacement. The coordinate method was found to be reliable for longitudinal studies in 3 dimensions and allows the evaluation of amount and direction of treatment changes. The orthodontic correction of the Class II was due to a combination of refrained forward movement of the maxillary molar and canine, slight outward transverse movement of the maxillary molar, and slight mesial movement of the mandibular molar, all on the Class II side.