3-D examination of dental fractures with minimum user intervention Andre Souza *a , Alexandre Falcão b , Lawrence Ray a a Carestream Health, Inc., Research and Innovation Labs, 1049 Ridge Road West, Rochester, NY USA 14615; b University of Campinas (UNICAMP), Institute of Computing, Av. Albert Einstein, 1251, Campinas, SP, Brazil 13083-852 ABSTRACT We developed a novel, powerful segmentation algorithm and an intuitive 3-D visualization tool for the examination of root fractures with minimum user intervention. The application computes and displays a suitable oblique orientation on a selected tooth by placing at least two splines (inside and outside of the tooth) in just one slice of the volume. Next, it allows the user to scroll through the volume, slice-by-slice in parallel to the plane, or to examine the tooth by changing the orientation of a 3-D object plane (called a virtual bitewing), which is placed, at the same time, in a volume rendition. Both the root canal and the root fracture are highlighted during the examination phase. Doctors (end users) are in control to quickly and confidently examine root fractures in 3-D, for any given oblique orientation, without worrying about missing a selected tooth. We have designed and implemented these algorithms using the image foresting transform (IFT) technique for interactive tooth segmentation and used a multi-scale parameter search for automatic oblique orientation estimation. Keywords: 3-D visualization, optimization, 3-D image segmentation, low-dose X-ray, CBCT, endodontics, root fracture 1. INTRODUCTION Cone-beam computed tomography (CBCT) is an X-ray imaging modality capable of acquiring three-dimensional (3-D) information of the human anatomy with a substantially lower radiation dose to the patient as compared to conventional medical computed tomography (CT) systems. The use of CBCT as a diagnostic tool for endodontics has increased the need for better image quality and the ability to display very low-contrast tissue regions usually associated with fractures within the tooth structure. Yet, recent clinical findings have reported the encouraging potential use of CBCT in the management of endodontic problems, 1-4 e.g., during root canal therapy, as shown in Fig. 1. 1 Vertical root fractures (VRFs) are severe tooth fractures that affect the tooth root, causing pain due to infection and inflammation, leading to tooth extraction. VFRs’ diagnosis remains a challenge, but supporting evidence indicate s that CBCT has the superior ability to detect VRFs as compared to periapical radiograph. 3 In this work, we developed a fast algorithm for interactive 3-D examination of root fractures. The application computes and displays a suitable oblique orientation from a selected tooth by placing at least two splines (inside and outside of the tooth) in just one slice of the volume. Then it allows the user to scroll through the volume, slice-by-slice, or to examine the tooth at the same time by changing the orientation of the 3-D object plane (called a virtual bitewing), placed in a volume rendition. Both the root canal and the root fracture are highlighted during the examination phase. The end users (doctors) are in control to quickly and confidently examine root fractures in 3-D for any given oblique orientation without worry about missing the selected tooth, which appears highlighted in red color on the oblique slices. In our approach, the user places internal and external splines on an orthogonal slice (i.e., sagittal, coronal, or axial) of each tooth of interest for examination. Each tooth must be marked by a spline of a distinct color, white being the color of the background spline. These splines are moving markers (seed voxels), which make this approach different from other interactive segmentation approaches, based on seed competition. That is, the user can deform a spline and add/remove *Send correspondence to andre.souza@carestream.com 1 Credit Encyclopedia Britannica.