Abstract: Objective：To build up and validate a system based on gyroscope to record human natural head position (NHP) and to transfer it into virtual surgical design system. Methods:Three dimensional (3D) mechanical gyroscope and 3D design software were integrated in the system. The protocol for recording and transforming NHP included four steps. Firstly, the gyroscope was CT scanned when its position was (0, 0, 0), a virtual model was built up by 3D reconstruction and considered as standard gyroscope model. Secondly, the gyroscope was bounded to the patient’s head using bite-jid and face bow. The NHP was recorded when the patient was looking himself into mirror. Thirdly, the virtual head of the patient was overlapped with standard gyroscope model. Finally, when pitch, roll and yaw of NHP were applied to the compound model, the virtual head was orientated to NHP. A standard cube model was used to validate the accuracy of the system. The cube was positioned 30 times, the real and virtual pitch, roll and yaw angles were recorded. The accuracy of the system was presented by the mean±SD of the Delta. the difference between the real and virtual pitch, roll and yaw angles were analyzed by paired t test，and their correlations were investigated by Pearson test. Results:The accuracy rates of the system were ΔPitch＝0.03± 0.28°,ΔRoll=0.03±0.23°,ΔYaw=0.07±0.49°. There were no significant differences between the real and virtual pitch, roll and yaw angles (P>0.05). The two positions were absolutely correlated at the level of α=0.01 (2tailed, r=1.00). Conclusion: The method of recording and transforming NHP using gyroscope is clinically applicable. The accuracy of transferring system meets the needs of virtual surgical design.

Key words: Head movements, Imaging, three-dimensional, Orthognathic surgical procedure