# Quality Control in Dental Cone-Beam Computed Tomography
## 1 Introduction  
Dental cone-beam computed tomography (CBCT) has been widely used in dental pulp diseases, periodontal diseases, pre-implant examination, temporomandibular joint structure examination, and orthodontic two-dimensional (2D) and three-dimensional (3D) measurement because of its high spatial resolution, low radiation dose, relatively small metal artifact interference, and simple equipment operation. Moreover, it has completely replaced the application of traditional medical computed tomography (CT) in these aspects and has become one of the important standard examinations and diagnostic means inatology. CBCT promotes the transition of dental diagnosis from 2D images to 3D images and truly expands the role of imaging from diagnosis to the image guidance of surgery. Many studies have shown that dental CBCT is significantly better than periapical radiography in terms of the accuracy, reliability, and sensitivity of dental pulpal and periapical diseases, periodontitis, external root resorption, root fracture, and other diseases in auxiliary diagnosis [1; 2; 3; 4; 5; 6; 7]. For example, [PERSON] et al. showed that the sensitivity and specificity of vertical root fractures diagnosed by periapical radiography were 37% and 95%, respectively, while the sensitivity and specificity diagnosed by CBCT were 79.4% and 92.5%, respectively [8]. [PERSON] et al. showed that the accuracy of CBCT for apical lesions was higher than that of periapical radiography [9]. [PERSON] et al. showed that all periodontal bone defects and truncation involvement could be diagnosed by CBCT, and the missed diagnosis rate of periapical radiography for vertical bone defects and frustration involvement was as high as 31% and 42%, respectively [10]. While meeting basicclinical needs, dental CBCT also involves the use of a large number of application software packages: not only free software packages provided by CBCT manufacturers, such as Invivo, NNT, Sidexis XG, and so forth, but also many third-party commercial software packages, such as EasyGuide, Implant 3D, SimPlant, Med 3D, NobelClinician, and so forth. These software packages are especially used for implantation, orthodontics, oral surgery, and dental restoration, and can help surgeons realize a series of operations such as pre-surgical analysis and planning, orthognathic simulation, pre-implant surgery design and implant guide production, projection measurement analysis, and so forth. While improving the accuracy and success rate of the operation, they also reduce the additional damage to the patient's soft and hard tissues. The number of medical accidents caused by poor medical equipment are increasing with each passing year [11]. The effective improvement in medical safety and reduction in casualties and economic losses caused by medical accidents due to poor medical equipment are important tasks and the mission of metrology researchers worldwide. Dental CBCT images are mainly used to analyze and evaluate patients' pathological process and, at the same time, estimate their subsequent disease development process, and then provide a reliable and scientific reference for clinical medical staff. If the CBCT image quality is inadequate, doctors are not provided with clear and effective 3D information about the tooth and maxillofacial structure, which may result in missed diagnosis or misdiagnosis. If the radiation dose of CBCT exceeds the standard requirement, the patient may be exposed to an excessive radiation dose. Therefore, a detection method more suitable for dental CBCT needs to be urgently developed. The projection data of conventional CT are usually one-dimensional, and the reconstructed images are two-dimensional. A 3D image is reconstructed by stacking multiple 2D slices. Dental CBCT uses a flat-plate detector, which generates 2D projection data. The 3D image is directly reconstructed from the 2D images. Dental CBCT uses divergent X-rays to increase the utilization efficiency of X-rays dramatically.