Akila Aiyar, Michel Dalstra & Tine Hjorth Aarhus University Evaluation of craniofacial symmetry and growth/treatment CHAnges in hemifacial microsomia patients by cone beam computed tomography Akila Aiyar, Michel Dalstra & Tine Hjorth Section of Orthodontics, Department of Dentistry, HEALTH, Aarhus University, Denmark EOS2017-I/842 BACKGROUND & AIM Hemifacial microsomia (HFM) is a congenital anomaly. The aim of the study was to assess and describe initial asymmetry of hard tissues and describe changes on the affected and non-affected side during treatment with functional distraction splints. RESULTS Although many parameters were assessed (Table I), we decided to focus on describing two of these: the gonial length (Fig. 3) and the gonial width (Table II). CONCLUSION The mandibular measurements showed an increase of ramus and condylar lengths during the course of treatment, and a correction of the cant of occlusal plane. The changes related to the cranial base reflect natural growth. Longer follow-up is required to assess the overall benefit of the treatment protocol. The study has demonstrated the difficulty in establishing appropriate stable structures as reference planes in these highly asymmetric patients. MATERIAL AND METHODS Fifteen HFM patients in the age range of 5 to 15 years were diagnosed and classified according to the Pruzansky/Kaban classification as type I, type IIa and IIb. Treatment started with an individually constructed distraction splint that allowed the patient to stretch the affected side and have an occlusion throughout the course of treatment. Cone beam computed tomography (CBCT) scans were taken during the course of treatment and the existing material was analyzed (Fig. 1). The images were converted from DICOM format into 3D visualization software for analysis (MIMICS). For each patient hard tissue measurements were performed on the initial and last available CBCT scan (Fig. 2). Hard tissue landmarks were identified, reference planes were defined and constructed and the degree of asymmetry of the affected versus non-affected side was assessed. Intra-observer reliability was assessed based on double measurements and the systematic error was determined based on the Method of Moments. Fig 1 b Fig 1a Fig 3 Table 2 Fig 1d Fig 1c Table 1 Fig 2 a Fig 2 b