Thesis (M.Sc.) - Cairo University - Faculty of Oral and Dental Medicine - Department of Orthodontics

Materials and methods: A cross sectional observational study was performed on 38 Egyptian adult subjects with an age range from 18-25 years having balanced facial proportions and Angle class I skeletal and dental relationship. After examination; impression taking was performed. Splint fabrication was done using 2-mm thickness hard vacuum sheets and the thickness was checked with the digital caliper to ensure 1-1.2 mm thickness of the sheet after fabrication. This splint was worn over the lower anterior teeth to ensure occlusal separation to preserve occlusal anatomy for registration and establish a minor hinge movement. All subjects and their dental models where scanned with the same i-CAT CBCT machine. All subjects where scanned with splints separating their occlusion. Subjects' dICOM data where segmented using In vivo dental anatomage 5.3 software and the 3D dental models where used to guide the opened mandible to centric occlusion (CO). Rectangular boxes where added using 3DsMax 2016 to aid in calculations and land marking. Finally, 3-matic software was used in registration and determination of the axis of mandibular rotation. Results: Regarding assessment of each condyle on its own, 6/76 axes where anterior to ramus, 5/76 where inter ramal, 6/76 are outliers due to amalgam artifacts and 59/76 where located posterior to the condyle. Regarding the unified axes, 3/32 where found anterior to ramus, 3/32 skewed axes and 26/32 where located behind the mandibular condyles. No statistically significant difference was found between the axis in the right and left side of the mandible in all 3 groups. Moreover, No correlation exists between the vertical distance and horizontal distance in both sides of all 3 groups

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