Three-Dimensional Cephalometric Analysis Using Computed Tomographic Imaging

Successful outcomes from the use of orthodontic devices are underpinned on their effective anchorage and the loading that they apply to the underlying facial structures. Anchorage plays an important role in determining the point of application of the corrective forces and subsequently the orientation of the resultant of these forces, which in-turn governs the outcome of treatment. Therefore, patient-specific design of anchors and their placement may benefit significantly from personalization using patient-specific and three-dimensional (3D) cephalometry. 3D cephalometry is therefore a first step to personalization of orthodontic treatment. In this feasibility study, we demonstrate the viability a novel image processing and surface analysis pipeline to quantify facial symmetry about the mid-sagittal facial plane, which may offer insight into optimal placement and orientation for implantation of orthodontic anchors, starting with patient-specific cone beam computed tomography (CBCT) images. Typical assessments of geometrical features/attributes of face include size, position, orientation, shape, and symmetry. Using 3D CBCT images in the DICOM image format, skull images were first segmented using a basic iso-contouring approach. To quantify symmetry, we split the skull along the mid-sagittal plane and used an iterative closest point (ICP) approach in order to rigidly co-register the left and right sides of the skull, optimizing for rotation, translation and scaling, after reflection of one half across the mid-sagittal plane. This was accomplished using an in-house plugin is developed for the open-source visualization toolkit (VTK) based 3D visualization tool, Paraview (Kitware Inc.). Finally, using a signed regional distance mapping plugin we were able to assess the regional asymmetry of regions of the skull (e.g. upper and lower jaw – specific targets for therapy) using colormaps of regional asymmetry (in terms of left-v/s-right side surface distance) and visualized the same as vector glyphs. The direction of these vectors is synonymous with anticipated regional forces required in order to achieve left-right symmetry, which in-turn may have value in surgical planning for orthodontic implantation. In sum, we demonstrate a workflow for computer-aided cephalometry to assess the symmetry of the skull, which shows promise for personalized orthodontic anchor design.