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 17.0 cm 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 -0.107 mm (SD = 1.148), and the average distance from the coincidental left porion in NHP was found to be 0.846 mm (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.

Bifid Mandibular Canal: A Case Review and Retrospective Review of CBCTs.

PURPOSE: This case presentation and retrospective review of cone-beam computed tomograms is to evaluate prevalence, classification, and demographics of bifid mandibular canals (BMC) to inform practitioners on this variation and avoid untoward complications due to failure to diagnose. MATERIALS AND METHODS: Two thousand one hundred thirty scans were evaluated by 2 oral and maxillofacial radiologists. BMCs were noted and classified according to Naitoh. Demographic data were also collected and analyzed. RESULTS: Twenty-eight patients were noted to have bifid mandibular canal, with an average age of 39 years (± 19.5), with no strong sex predilection. Patients (1.31%) were noted to have bifid canals. A greater percentage of patients were shown to have bilateral bifid canals (42.9%) versus either unilateral side (25% left, 32.1% right), but is statistically insignificant. Prevalence was greatest in types 1 and 3 (35.9% and 51.3%, respectively, P = 0.000011). Types 2 and 4 were much less common. CONCLUSION: BMCs are an important anatomic variation that has implications on any mandibular surgery, including implant surgery. Just more than 1% of patients have this variation, but failure to recognize this in a patient can result in poor outcome, as illustrated in the case presented.