Landmark-based midsagittal plane analysis in patients with facial symmetry and asymmetry based on CBCT analysis tomography.

PURPOSE: Reconstruction of the facial midplane is relevant in anthropometry, orthodontics, maxillofacial surgery, and the accurate measurement of symmetry deviation is relevant in many fields of medicine especially when planning surgical treatment. In the literature, three different means of midplane generation have been published; however, there is currently no consensus regarding the approach to use. Morphometric methods are used to determine the true midsagittal plane (MSP), but its use in clinical practice is difficult. A regression plane based on N­ANS-PNS landmarks reportedly approximates the morphometric MSP. As these points are vulnerable, we investigated which combination of landmarks can be substituted in symmetric and asymmetric faces. PATIENTS AND METHODS: Thirty symmetric and 30 asymmetric faces were analyzed on cone-beam computed tomography scans. A total of 50 regression planes were generated based on three unpaired landmarks and 35 regression planes were generated based the midpoints of paired landmarks. The Na-ANS-PNS plane was used as reference plane, and the mean angle between it and each generated MSP was calculated. The differences from the reference plane were compared by t­test between the groups. RESULTS: In the symmetric group, 86% of angles deviated by <5° using unpaired points, whereby 74% of angles deviated by <5° for paired points. Between the two groups 50% of planes from midline points, and 77% of planes from paired points were significantly different. All planes deviated more in the asymmetric group. CONCLUSIONS: The N­ANS-PNS reference plane can be substituted with the following combinations: ANS-G-Ba, ANS-G-S, ANS-S-De, PNS-G-Ba, PNS-S-Ba, PNS-ANS-G, and PNS-N-Ba.

Lower face cephalometry based on quadrilateral analysis with cone-beam computed tomography: a clinical pilot study.

OBJECTIVE: As most orthognathic surgeries focus on the lower face, the aim of this study was to transfer previously developed two-dimensional cephalometry-which is useful for surgeons in the orthognathic surgery of the lower face-to three-dimensional (3D) cephalometry by using cone-beam computed tomography (CBCT). We selected the quadrilateral lower face analysis developed by the surgeon Di Paolo, who focused only for the lower face and mentioned that data in millimeters are more easy to use than angles for surgeons. Additionally, we wanted to create a 3D lower face analysis approach based on quadrilateral analysis and establish a reference table for surgical planning. STUDY DESIGN: Three investigators assigned 16 landmarks on CBCT images from 30 patients with normocclusion. Intra-class correlation coefficients (ICCs) and standard deviations (SDs) were calculated according to each landmark. The maxillary and mandibular lengths and widths and the anterior and posterior lower facial heights (ALFH and PLFH) are presented as means and SDs. The asymmetry of the face was calculated with paired t test, and the coherence of the lower face was assessed with correlation coefficients (r) and regression models. RESULTS: The ICCs were ≥0.90, and the SDs of the landmarks were lower than 1.00 mm, except for the J-point, which was located at the junction of the anterior border of the ramus and the corpus of the mandible. The SDs of linear measurements were 3.06-5.20 mm, and there was no significant facial asymmetry. The r among the structures was greater than 0.3 in 13 of 15 assessments. Based on these values, we could establish a floating norm of the lower face using the following five regressions: one linear regression for the mandibular length, two quadratic models for the ALFH and PLFH, and two multivariate regressions for the posterior widths of the maxillae and mandible. CONCLUSION: The adaptation of quadrilateral analysis can provide accurate 3D characterization of the morphology of the lower face and the floating norm based on millimeter values, which is practical for surgeons. As the 3D extension of quadrilateral analysis could provide references of the lower face, which might be an accurate 3D approach for presurgical planning, the further investigation in bigger sample would be relevant in the practice.

[Di Paolo's cephalometrical analysis of lower face by means of Cone-Beam CT]. / Az alsó archarmad Di Paolo-féle vizsgálata Cone-Beam CT adatállományon.

OBJECT: 3D cephalometry is often the only way to set up accurate diagnosis and treatment plan in the field of reconstructive surgery. In these cases complement exposures are needed beyond common cephalograms with higher accuracy than conventional Cone-Beam CT. Consequently the aim of our study was to perform a complex 3D cephalometry. As the first step of this approach, was the 3D adaptation of DiPaolo's Quadrilateral technique, and to determine norms of references in lower face by means of CBCT. METHOD: Thirty non-orthodontic CBCT scans were selected for the digitalization. The most important inclusion criteria was Class I occlusion. Locations of 55 landmarks were signed three times by three observers by means of Cranio Viewer software. RESULTS: However Quadrilateral analysis contains only millimetric values we also integrate angles in the 3D version to determine the width of maxilla and mandible. In the 2D examination--where landmarks were projected to the middle plane. The SDs of the lengths were between 2,66 mm and 5,20 mm. The ratios of normodivergent lower face were significant different from the one by DiPaolo. In 3D adaptation there were no significant differences between the measurements of the two sides (p ≥ 0.05). We found mostly strong and significant correlations between each anatomical structure except of angles. CONCLUSION: Creation of 3D Quadrilateral cephalometry by means of strong correlation and norms of Class I occlusion provide a practical, reliable method to measure also the transversal asymmetry of lower face which is necessary part of 3D cephalometry.