Class II malocclusions in non-growing patients can be treated by orthognathic surgery or camouflaged with tooth movement. Fixed appliances such as the pendulum appliance or distal jets have been used to distalize maxillary molars to achieve a Class I molar relationships. Recently, removable clear aligners have been reported to achieve similar results with better oral hygiene. It is not clear in the literature whether these removable appliances can distalize maxillary molars dental tipping or

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... nslation. The objective of this study was to evaluate the dental and skeletal changes in three planes spaces using CBCT scans and compared the treatment changes with a control group of subjects with comparable Class II craniofacial morphology. Methods: A total of 8 patients (mean age = 16, SD = 5) with Class II division 1 malocclusions treated with maxillary molar distalization using clear aligners were recruited for the study. Four of these subjects had bilateral molar distalization. A total of 12 maxillary molars were evaluated for tooth movement in three planes of space using CBCT scans. These patients were compared with a control group of untreated subjects from the Bolton Brush study who were matched in craniofacial morphology, gender, and treatment length. The average treatment time for the treatment group was 24 months and the average time between the Bolton-Brush Growth Study. Sagittal and vertical changes were measured using the Pancherz analysis (Pancherz, 1982) . Transverse changes were measured by intermolar widths of the maxillary and mandibular molars. Data were analyzed using paired t test. Results: Significant sagittal changes were found with the forward movement of the mandibular incisors (Ii/OLP, 3.4mm), forward movement of the mandibular molars (Mi/OLP 3.6mm), and the change in molar relationship (-2.3mm). When the treatment changes were compared to control subjects, significant differences were found with the mesial movement of the maxillary molars (Ms/OLP, 0.5mm vs. 5.0mm, p<.0005). The change in molar relationship was -2mm vs. 0.5mm, p<.0004. The treatment group showed a reduction in overjet of -2mm compared to the control group of 0mm, p<.04. No significant vertical changes were found except for the maxillary incisor extrusion. No significant changes were found with transverse changes. Conclusions: Significant dentoalveolar changes including restraint in the forward movement of the maxillary molars can be expected to with sequential molar distalization with clear aligners. iii DEDICATION I would like to dedicate this thesis to my family who have supported me on my extended academic career. It's been a long road that will come to a promising end and I looking forward to moving onto the next chapter of my life. iv ACKNOWLEDGMENTS