Theoretical Basis for Virtual Skull Orientation According to Three-Dimensional Frankfort Horizontal Plane for Computer-Aided Surgical Simulation

Purpose:Computer-aided surgical simulation (CASS) is an evolving technology which has significantly affected surgical correction of dentofacial deformities, a key step of which is orientation of the virtual skull model to allow for analysis and treatment planning. Explored in this study is the coplanarity of a 3-dimensional Frankfort horizontal plane (3D FHP).Materials and Methods:The 122 17.0cm field-of-view cone-beam computed-tomogram (CBCT) scans were oriented to a 3D FHP using right porion, right orbitale, and left orbitale. The distance between the 3D FHP and left porion was then measured. The 18 CBCT scans were found to have external fiducial markers which were used for orientation into natural head position (NHP). The distance between left porion and a true horizontal plan coincidental with the right porion was measured. Concordance reliability measures were calculated to compare NHP to 3D FHP.Results:The average distance of left porion to 3D FHP was found to be -0.107mm (SD=1.148), and the average distance from the coincidental left porion in NHP was found to be 0.846mm (SD=2.611). Concordance reliability calculations shows little consistency between the 2 methods of orientation (P=0.838).Conclusions:The data shows coincidence between left porion and 3D FHP. Orientation of the virtual skull model according to 3D FHP offers a quick and easy method for this important step in CASS. Further study is needed for evaluation of this method in vivo.