This articles contains a review of the literature and recent research about Cone Beam Computer Tomography (CBCT) in Dentistry and its applications in the different dental fields such as Implantology, Periodontics, Endodontics, Orthodontics and Oral and Maxillofacial Surgery. You will also read information about the benefits of CBCT technology such as scanning time, radiation dose and image accuracy. 

Cone Beam Computer Tomography (CBCT) 

Cone Beam Computer Tomography (CBCT) is a relatively new radiographic technique which produces images in the axial, sagittal, coronal and even oblique or curved planes (multiplanar reformation). 
Computer Tomography was invented by Sir Godfrey N. Hounsefield in 1967, based on Röntgen’s discoveries. Hounsfield created the first functional CT unit working for EMI (record company) and on 1st October 1971, the first patient underwent a scan using this technology. Robles RA built the first CBCT in 1982 for angiography purposes. 
Computed tomography can be divided into 2 categories based on acquisition x-ray beam geometry; fan beam and cone beam; where in the fan-beam an x-ray source and solid-state detector are mounted on a rotating gantry while cone beam scanners are based on volumetric tomography, using a 2D extended digital array providing an area detector, combined with a 3D x-ray beam. 
Image of the Cone Beam CT principle.  
Image of Sir Godfrey N. Hounsefield. Nobel Prize in Physiology or Medicine in 1979.  

Advantages of the CBCT 

CBCT has many advantages compared with conventional CT in dentistry, especially, after the size of the CBCT equipment has been reduced to be installed in a dental practice. In terms of cost, it’s between 20-25% to the cost of a conventional CT. 
Among the advantages, it’s important to highlight the following: 
Scanning time: CBCT requires only a single rotation to acquire all basis images hence the time is rapid, between 10 to 70 seconds, compared with medical CT. By acquiring the images faster, motion artifacts due to patient movement are reduced as well. 
Low Radiation Dose: the effective radiation dose for a conventional CT range from 1400 to 21000 microsieverts meaning CBCT radiation dose is 96% to 51% less, with a range from 11 to 1073 microsieverts, depending on the field of view. The radiation dose and exposure for a CBCT can be reduced because the X-ray beam can be collimated, also a thyroid and cervical spine shield can be used to decrease the radiation dose. In the following table, you can check out the comparison of radiation dose between intraoral and extraoral conventional radiographs and CBCT in microsieverts.  
Effective dose 
Four-image posterior bitewings with photo-stimulable phosphor (PSP) or F-speed film and rectangular collimation 
Panoramic radiograph with charge-coupled device 
Cephalometric radiograph, posteroanterior or lateral with PSP 
5.1 - 5.6 
Full-mouth radiographs with PSP storage or F-speed film and rectangular collimation 
Full-mouth radiographs with PSP or F-speed film and round collimation 
Dentoalveolar CBCT (small and medium field of view [FOV]) 
11 - 674 (61) 
Maxillofacial CBCT (large FOV) 
30 -1073 (87) 
Image accuracy: the volumetric data set comprises a 3D block of cuboidal structures, known as voxels. The size of the voxels determines the resolution of the images. CBCT technology provides voxels resolutions that are isotropic (equal in all 3 dimensions) while in conventional CT, the voxels are anisotropic. The resolution obtained by the CBCT is sub-millimetre ranging from 0.4 mm to 0.125 mm. 

CBCT applications in Dentistry 

CBCT technology is currently utilised in many different fields in Dentistry such as Oral and Maxillofacial Surgery, Implantology, Endodontics, Periodontics and Orthodontics. 

CBCT in Implantology 

One of the key aspects to achieve success in Implantology is planning of the implant placement site. Bone density, anatomical structures and thickness of bone are crucial factors to determine during the planning phase for dental implant placement. 
When planning placement of dental implants on the mandibular posterior area, the inferior alveolar canal and its course must be considered while the maxillary sinus is the anatomical structure to be assessed when planning to place implants on the maxillary posterior area. 

CBCT in Endodontics 

CBCT technology provides great value in the endodontic field by helping in the diagnosis of periapical lesions due to pulpal inflammation, visualization of canals, interpretation of external and internal resorptions and detection of root fractures, among others. 

CBCT in Periodontics 

The use of CBCT technology in the field of periodontics hasn’t been studied as much as in other fields of dentistry but during the last years different papers have been published about the accuracy of CBCT for evaluation of periodontal status and assessing bone loss. 
In September 2018, Wenjian Zhang and col. published an article on Oral Radiology named “Comparison of periodontal evaluation by cone-beam computed tomography, and clinical and intraoral radiographic examinations” where they evaluated eighty patients retrospectively from the University of Texas School of Dentistry. The main objective of this study was to compare and correlate periodontal assessments among CBCT, clinical attachment loss (CAL) measurement and periapical (PA) and bitewing (BW) radiography. 
They concluded that CBCT is superior to conventional intraoral radiography (periapical and bitewing radiography) in providing topographical and morphological details for periodontal defects, demonstrating that CBCT is a reliable tool for periodontal bone level. They suggested as part of the conclusions of this study that it would be beneficial to develop an accepted protocol for the use of CBCT for periodontal assessment due to the radiation dosage of CBCT and the benefits of its application for diagnosis and treatment planning in patients with periodontal disease outweigh the risk associated with the radiation exposure. 
A more recent study “Cone-beam computer tomography performance in measuring periodontal bone loss” by Jingmei Yang and col. published on the Journal of Oral Science in February 2019; concluded that CBCT should be used with caution and only when necessary, to avoid radiation hazards. 
In this study, one hundred and eighty tooth sites from 13 patients were included. Three periodontists measured the distance between the cemento-enamel junction and alveolar bone crest, then CBCT images were acquired prior to periodontal surgery. Comparisons of measurements were made among three methods. This study indicates that the results of CBCT do not agree with results of intra-surgical measurement. 

CBCT in Orthodontics 

One of the main objectives for the use of CBCT technology in Orthodontics is to assess bony architecture and quantifying bone volume, especially, in the anterior region prior to start orthodontic treatment. By assessing the morphology of alveolar bone of anterior teeth to avoid excessive retraction or proclination of the anterior teeth that may result in iatrogenic complications such as, alveolar bone loss, fenestration, gingival recession, root absorption and dehiscence. Different studies have demonstrated that CBCT is more accurate than traditional radiographic studies as panoramic and periapical views. 
Another area where CBCT images have shown to be a useful tool is when assessing impacted or nonerupted teeth, especially, canines. When a patient is assessed regarding impacted canines by a dentist or orthodontist, the initial assessment is the clinical one by observation and palpation of the area. When the clinical examination is not sufficient to confirm the buccopalatal or buccolingual position of the nonerupted canine, the second step is radiographical assessment by intraoral and extraoral images. The most common intraoral radiography technique is the Clark rule by taking two periapical radiographs as recommended by this rule. 
The final assessment step is a panoramic radiograph or orthopantomography (OPG) which will provide a complete view of the mandible, maxilla and teeth but panoramic radiographs include well known errors superimposed structures and imaging artefacts, among others. 
In March 2019, Björksved et al published an article “Are panoramic radiographs good enough to render correct angle and sector position in palatally displaced canines?” on the American Journal of Orthodontics and Dentofacial Orthopedics. In this study, patients from 2 orthodontic centres of the Public Dental Health Service in Örebro and Eskiltuna, Sweden, were included. The inclusion criteria were patients with diagnosis of unilateral and bilateral palatally displaced canines planned for surgical exposure and orthodontic treatment, and panoramic radiographs and CBCT scans taken the same day. 
The conclusion of this study by Björksved and col were the following: 
The results showed a systematically more palatally displaced canine position in panoramic radiographs compared with CBCT images, but clinically the differences may be considered quite modest. 
The use of routine additional CBCT scans should be minimized. 
Panoramic radiographs could be considered good enough to assess palatally displaced canine position. 

CBCT in Oral and Maxillofacial Surgery 

This is the field of Dentistry where CBCT technology has had a major impact by becoming a useful tool in different areas of this speciality such as Facial Trauma, Temporomandibular Joint (TMJ) disorders, Oral Surgery, Orthognatic Surgery and Cleft patients. 
The use of CBCT in Orthognatic surgery has been useful to assess airway three-dimensional changes as a result of the movement of the mandible and the maxilla involved during an orthognatic surgery. 
There are different movements of the maxilla and the mandible like mandibular setback that might develop sleep-related breathing disorders such as obstructive sleep apnea by narrowing the pharyngeal airway space. On the other hand, a maxilla-mandibular advancement surgery has shown to be an effective surgical treatment of the obstructive sleep apnea by increasing the pharyngeal airway volume. 
In March 2019, Vijayakumar Jain and col published a study “Evaluation of three-dimensional changes in pharyngeal airway following isolated Lefort I osteotomy for the correction of vertical maxillary excess: A prospective study” on the Journal of Maxillofacial and Oral Surgery. The authors concluded that the airway volume area decreased at all three levels (nasopharynx, oropharynx and laryngopharynx) but the oropharyngeal level shown the highest postsurgical reduction though statistically insignificant. 
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