br Conclusion br Introduction Use of CBCT in dental procedur

Conclusion
Introduction Use of CBCT in dental procedures has increased in recent years due to its low cost, fast image production rate and its low radiation dose in comparison with CT. CBCT appears to have a high potential in the diagnosis and treatment planning, especially in implant treatments, by providing three-dimensional images [12,30]. Although, it is a widely used method for 3D radiographic assessment in dentistry, it should not be elapsed that there are intrinsic limitations and artifacts regarding this technique. Artifacts are induced by discrepancies between the mathematical modeling and the actual physical imaging process [17,29]. An image artifact may be defined as a visualized structure in the reconstructed data that is not present in the object under investigation [4]. CBCT image artifacts may be attributed to small field of view (FOV) or divergence of the cone beam resulting in aliasing artifacts, also small flat panel detector (FPD) may result in ring artifacts. In addition, unexpected movements cause double contours called motion artifacts [13,29,32] which can be solved by sufficient fixation of the patient\'s head during the scan and increase in the mechanical stability of the system [4,8,13,29,32,36]. Moreover, imaging of highly absorbing materials may cause missing value artifacts, beam hardening artifacts or exponential edge gradient effect which appear as cupping artifact, streaks and dark bands between dense objects or streaks at sharp edges with high contrast to neighboring structures [27,28]. Beam hardening artifact is one of the most prominent sources of artifacts [4,5] caused by Wnt agonist 1 of lower wavelength rays when passing through the object. The lower energetic (lower wavelength) rays of the polychromatic spectrum emitted by the X-ray source may suffer substantial absorption when passing through the object under study. The denser the object and the higher its atomic number, the larger the range of absorbed wavelengths [29]. Examination of metal bodies as dental fillings or dental implants usually uses high-density metal materials, such as gold alloy, amalgam and titanium which cause severe beam hardening and scattering effect artifacts [15]. Metal artifacts influence the image quality by reducing the contrast, obscuring structures and impairing the detection of areas of interest, thereby making the diagnosis difficult and time-consuming [25,34]. Methods for reducing metallic artifacts in CBCT images have been documented, but these techniques cannot completely remove streak artifacts. Previous studies have evaluated metallic artifacts in CBCT images [29]. However, the majority of these studies have been qualitative ones. A few studies have quantitatively compared CBCT X-ray machines [12].
Materials and methods
Results
Discussion Evaluation and comparison of different CBCT machines in relation to the extent of metallic artifacts are very important because in some cases the artifacts are so extensive that image quality decreases or even the image is distorted [35,38]. From genome issue, this study was designed to quantitatively evaluate the artifacts produced by different metallic restorations using four cone-beam computed tomography scanners. Human subjects were excluded from the study and the diagnostic capabilities of the imaging modalities were investigated on dry mandibles and extracted teeth to simulate the real clinical situation. Another reason was to avoid interference of factors that could impede the quality of examination as motion of patient, as well as the possibility of presence of other metallic structures that could affect the quality of the final image other than the tested factors [1]. The lack of clear boundaries to metallic artifacts in CBCT images means that no standard method of quantifying the artifact area exists. We therefore established threshold values for the black and white components according to the method reported by Ref. [33]. The results of the present study showed that a statistically significant difference was found between the different CBCT scanners regarding the values recorded in crown, MO, MOD, inlay in both volumetric and thresholding methods which may be due to different type of detectors, FOV or voxel size [26].