Three-dimensional determining the midsagittal plane of the facial skull on CBCT volume tomogram

Objective: As the midsagittal plane often plays an important role in presurgical planning, the aim of this study was to create a reliable midsagittal plane of the skull based on three-dimensional database. Methods: Three observers detected 25 cephalometric points on 60 random cone-beam volume tomograms three times. The points were assigned to three groups: 1. paired points of maxillae, 2. paired points of the mandible, 3. unpaired midpoints. The standard deviation of each landmark was calculated and the intra- and inter-examiner reliability was assessed with intraclass correlation coefficient (ICC) and analysis of variance (ANOVA). Three regression planes were created from the points of each group and the most reliable regression plane was determined based on the mean distance of the remaining landmarks from the planes. In the most accurate group we analyzed which combination of three points provide a reliable facial symmetry plane and which points can substitute each other. Results: The ICCs were high≥0.90, the SDs were lower than 2.00 mm except for Arcus Zygomaticus, bilateral Apertura Pyriformis (y, z), Foramen mentale left (x, z) and Crista Galli. The mean distance and SD of the measured points from the regression plane constructed of the unpaired midpoints was the lowest as compared to the plane of mandibular and maxillary points. In this group the following combinations framed the most accurate midsagittal planes: N-S-B, N-S-D, G-S-B and G-S-D. Conclusions: Thanks to the suitable landmarks, a reliable midsagittal plane can be created with this method, even if some landmarks are injured.