With the development of dental cone beam computed tomography（CT）, we can easily grasp the three dimensional relationship between lesions in the oral cavity and anatomical landmarks. Perhaps, dental cone beam CT will become more widespread in the dental fi eld. However, its clinical applications for dentalrelated lesions has remained obscure, and many dentists at present might be confused concerning the appropriate uses of dental cone beam CT. In the present review, clinical applications in dental cone beam CT for dental-related lesions based on the Guidelines（Basic Principles for Use of Dental Cone Beam CT）by the European Academy of Dental and Maxillofacial Radiology were considered.

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Cone Beam CT（CBCT），which was developed in 1998，is a very useful tool for diagnosis of oral and maxillofacial lesions．Many types of CBCT have been sold around the world，and the diffusion rate increases year by year. Although flat pane（l FPD）or image intensifier（I.I.）technology is used as the digital detector for CBCT now，FPD will become mainstream in the future．Hybrid units combining CBCT with panoramic tomography have been developed recently. The basic principle of CBCT is different from that of medical CT．The rotation of the cone beam X-ray and the detector around the patientʼs head produce multiple projection images（volume data）．Volume data of CBCT constituting a cylindrical or spherical volume provide detailed three-dimensional images of oral disease. Some CBCT machines allow the operator to adjust field of view（FOV）protocol to small，medium，or large．More modern systems are extending this limit still further．Small FOV Cone Beam CT machines offer higher spatial resolution，compared with full-head FOV. The radiation doses from CBCT are generally higher than conventional dental radiography（intraoral and panoramic），but lower than medical CT scans of the dental area．Dose is dependent on equipment type and exposure settings，especially the field of view selected. CBCT has the following particular shortcomings； 1）CBCT is unable to discriminate soft tissue．Contrast resolution is much lower than that of medical CT； 2）CBCT does not have a CT number； 3）Artifacts are more pronounced in CBCT than medical CT.

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Dental cone beam computed tomography（CBCT）systems have been designed for imaging hard tissues of the oral and maxillofacial region．This technique provides relatively high spatial resolution and 3-dimensional information concerning of fosseous structures，compared to conventional images．Recently，CBCT is being increasingly used for oral and maxillofacial imaging．However，most dental practitioners are familiar with 2-dimensional images produced by dental X-ray apparatus，panoramic tomography et al．Therefore，there are many dentists hesitating about its use．This article，provides an overview of maxillofacial CBCT systems and reviews the specific application of various CBCT display modes to clinical dental practice.

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The introduction of cone-beam CT (CBCT) heralds a true paradigm shift from a 2D to 3D approach to data acquisition．Only one rotation of the gantry is necessary to acquire sufficient data for image reconstruction．Advantages such as high spatial resolution，lower effective dose，low cost and so on have encouraged the widespread use of CBCT，in spite of many artifacts induced by discrepancies between the mathematical modeling and the actual physical imaging process．Therefore，many manufacturers have now developed various CBCTs．It is difficult for general practitioners to understand the advantages and disadvantages of each different type of CBCT．In addition，the terminology and technical device properties are not familiar to general practitioners． However，there are several fundamental matters that can be used to evaluate the performance of CBCTs．The spatial resolution，the contrast，and the graininess are three fundamental factors associated with the image quality．The resolution properties obtained by CBCT are superior to those obtained by multi-detector row CT (MDCT)．In addition，the size of the voxels is strongly corrected to the special resolution，although this is also affected by the physical properties of the detector，and the reconstruction functions．The scatter radiation and beam hardening cause poor image contrast and bad uniformity of the density values．A characteristic artifact due to halation from the image intensifier (I.I) also reduces the image quality．A lower radiation dose usually results in poor noise properties in CBCT．Therefore， various attempts to improve the image quality are currently in progress． The effective dose is another important factor for the performance of the CBCT．Although the effective dose of CBCT is generally lower than that of MDCT，there is wide variation among CBCTs．It is necessary to select a small field of view in order to optimize the dosage． This review evaluates several factors，including those listed above．We expect that this review will be helpful for the reader in evaluating the performance of the CBCT．

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