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

The aim of this study was to generate 3D norms for a sample of adult subjects with normal accepted occlusion and balanced facial profile in centric relation (CR) using interocclusal mandibular splint and compare it to norms in simulated centric occlusion (CO).Materials and methods: A cross sectional observational study was performed on 37 Egyptian adult subjects ( 25 males and 12 females ) with an age range from 18-25 years having balanced facial proportions and Angle Class I skeletal, molar and canine relationship. All subjects had a full permanent dentition with the exception of the third molars. Arch length discrepancy ranged from 1 to 3 mm in each jaw within the three dimensions (vertical, anteroposterior and transverse), 2 to 3 mm overjet, 20-30% overbite and coincidental facial and dental midlines. Subjects with craniofacial deformities, pregnant female subjects, those who had been exposed to x-ray radiation within the last six months and those who had received previous orthodontic treatment were excluded from the study.First visit, 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.Thirty seven CBCT images were collected using the i-CAT CBCT machine. The subject`s head was oriented before imaging in the natural head position. The three-dimensional assessment was performed by In Vivo Dental Anatomage 5.3 software. The inter- and intra-observer reliability was confirmed after the 3D landmarks identification for randomly selected 10% of the sample by two observers, the researcher (observer1) and a colleague (observer2), and only for the researcher to do it twice with a gap of seven days between them

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