Comparison of conventional and cone beam CT synthesized cephalograms

Objectives: To compare cephalometric measurements from synthesized cone beam CT (CBCT) lateral cephalograms using orthogonal and perspective projections with those from conventional cephalometric radiographs and dry skulls. Methods: Ten skulls were imaged using CBCT and conventional cephalometry. CBCT volume data were exported in DICOM format and imported in Dolphin 3D (pre-release version). Orthogonal and perspective lateral cephalometric radiographs were created from 3D virtual models. Nine linear and five angular measurements were made in Dolphin at three different times. Three calliper measures of midsagittal landmarks were made directly onto skulls. Perspective and conventional image measurements were corrected for known magnification. Reproducibility of measurements was assessed using multivariate analysis of variance (MANOVA). Linear and angular measurements were compared between image modalities by measurement using a repeated measures MANOVA model. Differences and absolute value of differences between image measurements and skull measurements were assessed using analysis of variance (ANOVA). Results: Measurements were not different between the imaging modalities (P > 0.05), except for the mandibular unit length (P = 0.01). Linear midsagittal measurements were significantly greater than skull measurements for perspective CBCT and significantly less than skull measurements for conventional images (P = 0.003). Precision of orthogonal CBCT midsagittal linear measurements was significantly better than the other modalities (P = 0.007). Orthogonal CBCT projections provided more accurate midsagittal skull measurements than perspective CBCT or conventional cephalometric radiographs. Conclusions: CBCT can reproduce conventional cephalometric geometry with similar precision and accuracy. Orthogonal CBCT projections provided greater accuracy of measurement for midsagittal plane dimensions than perspective CBCT or conventional cephalometric images.