Detection of Vertical Root Fractures by Using Cone Beam Computed Tomography with Variable Voxel Sizes in an In Vitro Model Senem Yig˘ it O ¨ zer, DDS, PhD Abstract Introduction: The aim of this study was to compare the diagnostic accuracy of cone beam computed tomog- raphy (CBCT) scans with different voxel resolutions in the detection of simulated vertical root fracture (VRF). Methods: Sixty teeth, 30 with root fractures and 30 without, were examined through i-CAT tomography at 4 different voxel resolutions (0.125, 0.2, 0.3, 0.4 mm). Three observers scored the presence of VRF in all modalities. Sensitivity, specificity, likelihood ratio, and accuracy were calculated for each modality. Results: Chi-square statistical analysis showed no significant difference among the resolutions or observers. However, positive likelihood ratio values of 24.5 for a 0.125-mm voxel, 24.25 for a 0.2-mm voxel, 13.2 for a 0.3-mm voxel, and 13 for a 0.4-mm voxel were found. Accuracy results confirmed the likelihood ratios as 0.97, 0.96, 0.93, and 0.92, respectively. Conclusions: CBCT scans were reliable in detecting simulated VRF, and a 0.2-mm voxel was the best protocol, considering the lower x-ray exposure and good diagnostic performance. (J Endod 2011;37:75–79) Key Words Cone-beam computed tomography, diagnosis, vertical root fracture, voxel V ertical root fractures (VRFs) are difficult to diagnose by conventional periapical radiography (CPR), and they can be overlooked if the x-ray beam does not pass along the fracture line. Thus, 2 or more radiographs taken at different angles are rec- ommended (1, 2). Two-dimensional (2D) intraoral radiography systems fail to provide information regarding teeth and adjacent structures in the third dimension, and the superimposition of other structures further limits sensitivity (3). Thus, a need exists for an imaging system that provides 3-dimensional (3D) information in treatment assessment of root canal systems. Recently a 3D diagnostic imaging system, cone beam computed tomography (CBCT), has been reported to be more accurate than CPR for detecting longitudinal root fractures with high image quality, permitting direct visualization of fracture lines, which are masked in CPR (4, 5). CBCT scans have been found to be more accurate in detecting VRFs in many studies (5–10). CBCT has been found to perform better than CPR and other intraoral techniques in detecting VRFs; however, many studies have concluded that the radiation doses from CBCT were higher than from conventional dental radiography techniques (11). Briefly, digital images are composed of elements called pixels. A pixel is a picture element, a square in a 2D matrix. Each pixel has a specific size, intensity value, and loca- tion within the matrix. A voxel is a volume element, and it is the cubed form of a pixel, having a third dimension. Three-dimensional images are composed of voxels instead of the pixels in 2D digital images. The size of each voxel is determined by its height, width, and thickness, and a voxel is the smallest element of the 3D radiograph image volume (12, 13). CBCT images use isotropic voxels, meaning they have the same height, width, and thickness. The isotropic nature of the voxels affords the same quality as the original image in reconstructions. Image quality has been described as the visibility of diagnostically important struc- tures in the CT image (14, 15), and a number of factors affect image quality such as the milliamperage settings, voxel size, field of view (FoV), and detector type of the scanner (15–17). Diagnosis with CBCT offers 3D images without superposition of adjacent structures, and it is also a noninvasive technique with high accuracy (18–23). However, the radiation dose is equivalent to that needed for 4–15 panoramic radiographs (11), and unfortunately, image quality is directly related to radiation expo- sure (24). Voxel size has been reported to have a positive correlation with image quality (contrast and resolution) and exposure dose (6, 25). ALARA is the acronym for as low as reasonably achievable and is a basic principle for diagnostic radiology. Keeping the dose as low as possible while still obtaining the needed information constitutes the basis of this principle (26). It is known that with smaller voxel sizes, radiation exposure would be higher (12, 24, 27). Without sacrificing image quality and adopting the ALARA principle, the ability to select various voxel settings would be helpful in reducing the radiation dose to the patient. Thus, we compared the diagnostic accuracy of different voxel sizes for the detection of experimentally induced VRFs. Materials and Methods The experimental group consisted of 60 recently extracted human maxillary premolars, inspected with a stereomicroscope (MT4200 binocular; Meiji Techno From the Department of Operative Dentistry and Endodon- tics, Faculty of Dentistry, Dicle University, Diyarbakir, Turkey. Address requests for reprints to Dr Senem Yig˘ it O ¨ zer, Dicle University, Faculty of Dentistry, Department of Operative Dentistry and Endodontics, 21280, Diyarbakir, Turkey. E-mail address: senemygt@hotmail.com. 0099-2399/$0 - see front matter Copyright ª 2011 American Association of Endodontists. doi:10.1016/j.joen.2010.04.021 Basic Research—Technology JOE — Volume 37, Number 1, January 2011 Detection of Vertical Root Fractures with CBCT with Variable Voxel Sizes 75