The Role Of Cone-Beam Computed Tomography In Dentistry: A Review

Discuss about the The use of cone-beam computed tomography in dentistry.

Introduction to Radiography

This section will comprise of a review of scholarly articles that encompass current theoretical and methodological knowledge on substantive research findings, which in turn will contribute to the topic of interest. The section will discuss published information relevant to the two research aims, in an organized pattern by summarizing the pertinent findings. The first aim of the research is to investigate whether the endodontists undertaking the CBCT scans follow the justification criteria that are set out by the AAE ESE position statement. Radiography refers to the imaging technique that depends on the use of x-rays for viewing the internal forms of a biological object. The process of radiography encompasses creation of a beam of electromagnetic radiation, or x-rays that are produced from a generator and projected towards the object, currently being viewed. The discovery of x-rays is credited to Wilhelm Röntgen, the German physicist, who was the first person to systematically conduct a study on its functions. X-rays were found to get emanated from discharge tubes, commonly known as Crookes tubes, which produced free electrons by residual air ionization. Radiological cars were developed in 1914 for supporting the soldiers injured during World War 1. A new invention, commonly known as computed tomography was developed in the year 1972 that brought about major transformation in diagnostic medicine. No significant changes were observed in geometry for imaging dentition since 1896. CBCT or cone beam technology, the medical technique based on x-ray computed tomography has gained attention in the treatment, planning and diagnosis of implant dentistry. This technique was introduced in 1996 in Europe by QR s.r.l. (NewTom 9000) and in 2001 in the US market. The role of CBCT in implant radiography can be attributed to the fact that the dental cone beam has the property of offering valuable information regarding the planning and assessment of surgical implants and is now one of the most preferred options of pre-surgical dental implant assessments (Bornstein et al. 2014). The technique also has the capability of presenting undistorted views of dentition that are accurately used for visualising non-erupted and erupted teeth, and tooth roots that cannot be viewed by 2-d radiography.  

The major deleterious effects of ionising radiations are primarily categorised into two different types namely, stochastic and deterministic effects. The deterministic effects occur when the exposure threshold is exceeded. Deterministic effect severity is directly proportional to exposure dose. Some of the most common effects are cataract, sterility, skin erythrema, and radiation sickness. However, the stochastic effects follow some linear-no-threshold hypothesis that occurs due to ionising effects of symmetrical translocation. These lead to cancer, and several hereditary defects such as, Down syndrome. The risk of cancer development is found to follow some linear pattern with an increase in radiation dose (Palma et al. 2013). The effective doses of ionising radiation are used for measuring them in terms of their harm inflicting potential and are measured as Sievert (Sv) units. This unit also takes into consideration the kind of radiation and organ or tissue sensitivity. The stochastic effects of cancer appear several decades later and their likelihood is proportional to the dose of radiation. One particular study suggested that 35.6% general private practitioners refer CBCT. Oral radiologists (14.2%) and surgeons (21.9%) are found to be the frequent groups who referred CBCT to the patients, followed by prosthodontists and orthodontists (Warhekar et al. 2015). The technique is also referred for the use of conservative dentistry, oral diagnosis, and general dentistry. Another study provided evidence for the fact that periodontics (21%), prosthodontics (14%), and dental professionals with advance education in dentistry (13%) were some of the most requested resident providers, with regards to use of CBCT (Fewins 2017). The mean age of patient referrals was found to be 45 ± 21 years with a predominance of 62% women. Most patient referrals were made from periodontolgy specialists (17%) and maxillofacial surgeons (51%) (Arnheiter, Scarfe and Farman 2006).

Introduction of CBCT in Dentistry

The use of the CBCT technique commonly spans a plethora of clinical procedures and specialties namely, orthopaedics, radiotherapy; dental/maxillofacial, urology, and other interventions. The number of CBCT scans and intervention complexity also control the range of doses. Radiation protection guidelines involve standard measurement of image quality and doses across different manufacturers (Rawson 2015). Availability of aggregate dose is recommended (Paul, Mbalisike and Vogl 2013) for equipment that are used in CBCT and fluoroscopy. Reduction of dose include designing the CBCT equipment meeting the mechanical and electrical safety requirements, containing electronic displays on the operator consoles, and presence of low dose protocols. Selections of high dose protocols in cases that involve visualisation of soft tissues such as, intracranial haemorrhage, abscess or tumors are some of the guidelines (de Gonzalez et al. 2013). Creating a balance between the exposure and the quality needs help in optimising radiation dose. Reduction of mA and kVp for the equipment have been found to create no significant loss of the quality of images. Another procedure for radiation protection encompass bringing about a reduction in the size of X-ray beams to minimum needed size for imaging the object/organ of interest (Rehani et al. 2015). This has been found effective in limiting the dose of harmful radiation exposure to the patients, in addition to improving the quality of images by scatter reduction. Imaging doses have been found to account for an estimated 2% or more of target doses, with respect to first generation, linac mounted kV CBCT systems (SEDENTEX CT 2011). Thus, radiation protection involves evaluation of the daily CBCT imaging for all patients, for sensitive organs having lower thresholds for non-stochastic effects and pediatric patients having high radiation sensitivity. Use of low-quality neurointervention scan protocols, typically using fewer number of CBCT projections, are usually considered sufficient for producing high-contrast structures such as, bony anatomy or contrast-enhanced vessels. Maintaining sufficient distance from the source of x-rays and use of shields are also effective radiation protection steps.

Imaging plays an important role in endodontics that is routinely utilized to get a perfect picture of tooth anatomy along with surrounding structures. Conventional X-rays use analog film or digital receptor in two-dimensional image of the object. It has certain limitations that are overcome by three-dimensional radiographic techniques in endodontic practice. Radiographs are the most accurate diagnostic aids that are used by endodontists for diagnosing diseases that affects mandible and maxilla (Patel et al. 2015). With this technique, it is difficult to interpret the X-rays that give picture of the surrounding structures while superimposing them. Radiographs are beneficial part of root canal therapy for the diagnosis and treatment and conventional X-rays do not demonstrate accurately the presence of lesions, its real size and spatial relationship with the tooth’s anatomical structures. The resolution of conventional X-rays is inferior and it is not adequate in performing diagnostic tasks in endodontics. It has further disadvantages as it is unable to manipulate images, require high radiation dosage, cannot archive images and in increase in time between exposure and interpretation of images.

Applications of CBCT in Endodontics

In the recent years, CBCT has been specially developed to produce three-dimensional images (3D) that are undistorted providing information on maxillofacial skeleton with 3D images of teeth and its surroundings. This method is beneficial as compared to conventional radiography for endodontic diagnosis with numerous advantages described in the subsequent section. Instead of fan-shaped in regular computerized tomography (CT), CBCT gives cone-shaped beam used by endodontists as it is more accurate and provide appropriate diagnostic information than histology or biopsy for the evaluation of large periapical lesions. CBCT has specific applications in endodontics including diagnosis of canal morphology, endodontic pathosis, assessment of non-endodontic regions, root trauma and fracture evaluation, internal and external root resorption, pre-surgery planning and invasive cervical resorption. Early periapical diseases can be accurately detected using CBCT as compared to conventional X-rays with actual picture of size, nature, extent and position of resorptive and periapical lesions (Ahlowalia et al. 2013). Root canal and fracture anatomy and bone topography surrounding the teeth can also be diagnosed using CBCT (Neves et al. 2014). The scans obtained using this technique are desirable and easy to access the posterior teeth before periapical surgery with accurate determination of thickness of cancellous and cortical bone as the inclination of roots is related to surrounding jaw. This technique also provides clear pictures about anatomical structures like inferior dental nerve and maxillary sinus to the root apices (Deepak et al. 2012).

CBCT is widely used in endodontics for the evaluation of root canal, study of internal and external macro morphology in 3D, reconstruction of teeth, root canal preparation, coronal micro leakage evaluation, and bone lesions detection and in experimental endodontology that is used for accurate identification of apical periodontitis. This technique can determine the differences in density between granulomatous tissue and cystic cavity making it preferable for non-invasive diagnosis (Durack and Patel 2012). It allows evaluation of each root and the surrounding structures or areas of interest that can be compared over time. CBCT has pre-surgical application in locating lesions, proximity to maxillary antrum and mandibular canals (Pertl et al. 2013). It has great advantages that include higher resolution, increased accuracy, lower radiation dose and reduction in scan time. There is also anatomic noise elimination, facilitation of assessment of important features like diagnosis, treatment and management in endodontics.

CBCT has major advantage over CT scan in terms of substantial reduction in radiation exposure with X-ray beams that are pulsed. They are easy to use and require less space making it suitable for dental practice. The images obtained are displayed in axial, orthogonal planes, coronal and sagittal simultaneously. This display of the tooth allow clinicians to get an accurate anatomy of entire tooth and its surrounding tissues providing superior scans for the assessment of hard dental tissues.

Advantages of CBCT over Conventional Radiography

Although, CBCT overcome various limitations of conventional radiography, the images produced by this technique have some significant problem. It affects the quality of image in terms of diagnostic accuracy as the CBCT beam is scattering and hard due to high-density structures in the surrounding like metallic posts, enamel and restorations, diagnostic value lowering of root-canal perforations and internal root resorption. It is suggested that CBCT should be combined with periapical radiographs for producing accurate pictures of tooth and its surrounding tissues (Patel et al. 2013). In addition, scan times in CBCT are lengthy having 15-20 seconds that requires patients to stay still during the procedure (Gümrü and Tarç?n 2013).

Although, ionizing radiation in CBCT use is not without risk, therefore endodontists need to follow guidelines before administration. It is critical for them to take precautions to keep the radiation exposure minimum for the patient. Moreover, every endodontic image should be prescribed individually, where benefits outweigh potential risks associated with the technique use. CBCT use in every day practice raises concerns for the endodontic practitioners regarding necessary training and experience in order to take and evaluate CBCT scans efficiently. This is a major diagnostic challenge among endodontists that demand comprehensive knowledge and skills to master the technical operation as well as understand the radiographic features of neck and head anatomy, pathology and technique use that is beyond the experiences of endodontic practitioners (Kamburo?lu, Tsesis and Rosen 2017). Many practitioners provide information to patients regarding CBCT imaging from the perspective of technology assessment position like 3D image instead of 2D. However, there is existence of fundamental distinction where they need to determine the overall benefits of the imaging and its relation to the specific patient outcomes. The practitioners should be accountable for their actions in CBCT use, as they need to exercise judgment about various aspects of ethical, moral and legal regulations like patient safety. Based on these professional responsibilities, countries like United Kingdom (UK) have published guidelines regarding CBCT training with advice from Health Protection Agency (Donaldson, O'Connor and Heath 2013). These standards published in the documents are not appropriate in other countries and therefore for the delivery of care, AAOMR gave the first position statement on the performance and interpretation of CBCT use by endodontists (Fayad et al. 2015). The practitioners have a moral obligation to achieve necessary skills and experience to perform this technique through fulfilment of education standards and continuous professional development (CPD) training programs. Ersan et al. (2017) highlighted the fact that there is scarce evidence regarding the extent of CBCT use and its incorporation into dental teaching. Competencies were determined regarding CBCT use among under and postgraduate dental students in Europe and the results suggested that about 53.7% out of 80% dental students feel that prior CBCT training is required to be competent in using this technique. Majority of dental schools in the country have CBCT machine, however further updating of competencies are required for defining limitations and responsibilities of endodontists on this technique use.

Radiation protection guidelines for the use of CBCT in dentistry

Other dental staffs (clinical and non clinical) should have proper training regarding CBCT use and demonstrate good understanding of national guidelines that ensure continuous patient safety with minimum radiation exposure. The working arrangements are also different and so the practitioners should be aware of the differences in the radiation magnitudes in dental CBCT use. The practitioners should have formal training in context to radiation safety and adequate knowledge on safe use of the CBCT machine.

Brown et al. (2013) highlighted the fact that CBCT use in endodontics is a new technique in imaging modality that is widely used by dentists for the examination of hard tissues in maxillofacial regions. There is awareness witnessed in UK dental setting where the European Academy of DentoMaxilloFacial Radiology recognizes that endodontists should receive training in CBCT dental imaging; however, there is limited information available on how this training is applied and interpreted by them (Harris et al. 2012). It highlighted that training requirements regarding CBCT imaging is recognized at two levels in Europe. The Level 1 is aimed at training the dentists who prescribe imaging using CBCT like understanding appropriately the obtained reported images. Level 2 is the advanced level where it covers the skills that are needed for justification, carrying out and interpreting CBCT examination. Abella et al. (2015) also highlighted that CBCT operators need to be adequately trained for interpreting the images because it is different from conventional radiography. A rational and cautious approach along with basic training requirements on CBCT imaging should be followed regarding CBCT imaging in endodontics. Training is also required regarding hardware use in CBCT and image interpretation in endodontics.

As outlined by Qirresh, Rabi and Rabi (2016) CBCT use in dentistry is widespread and require specialized training in using it. After conducting an online questionnaire, it was found that CBCT is an advanced technique and it is realized and quite accepted that dental specialists require training. However, definite knowledge gap is present on CBCT use among the dental specialists. This highlights that training and development is mandatory prior to this technology use. Another study conducted in Iran by Tofangchiha et al. (2015) also stated that Iranian dentists have an average level of CBCT knowledge and require qualification programs for strengthening awareness among them regarding its application. Prior to its use, it is crucial to assess the skills and knowledge of the dentists on CBCT use and interpretation of obtained results. Therefore, from the above discussion, it is evident that specialized training is required on CBCT use among endodontists.

The guidelines and position statements provide help to all dentists in the evaluation of their patients and facilitate the process of performing high quality endodontic diagnosis and treatments. Major recommendations formulated by the AAE (Evans et al. 2013) focus on considering intraoral radiographs as the primary imaging modality for endodontic evaluation, and limited CBCT as the diagnosis choice in patients presenting non-specific or contradictory clinical signs. Furthermore, the statement also suggests that limited CBCT should also be considered for initial teeth treatment in cases that encompass complex morphology and extra canals. In addition, the endodontists should also consider CBCT in cases when preoperative CBCT has not been conducted. The criteria of using CBCT is followed in most endodontic applications owing to its benefits in increasing the spatial resolution, which in turn improves the accuracy of specific tasks such as, observing small features that include accessory canals, apical deltas, root fractures and calcifications (Scarfe et al. 2009). This is in accordance with the recommendation that a small FOV should be put to use for managing limited dento-alveolar trauma, luxation and root fractures. Studies (Machado 2015) have also provided evidence for the fact that CBCT has advanced in the form of a technology that is preferred by a range of scientists in the form of an imaging technique. Dentists have been identified to use the procedure as the standard imaging process that helps them to conduct dental implants, orthodontic, orthognathic and endodontic cases. The dentists follow the recommendations regarding use of CBCT because CBCT scanning has the potential to deliver doses that are an estimated 50-100 times less than conventional CT doses (Qirresh, Rabi and Rabi 2016). Furthermore, adherence to the recommendations can also be attributed to the fact that the technique has the capability of presenting a detailed and precise evaluation of the dental implant site (Dula et al. 2014), which in turn is facilitated by an accurate cross-sectional and three-dimensional image of the dental anatomic structures in safer and lower doses. In addition, dentists, who use this technique owing to its benefits related to oral and maxillofacial radiology, follow most of the recommendations.

Recently dental professionals have identified the limitations to two-dimensional radiographs and have begun using the CBCT technique for all endodontic procedures for histologic sectioning of the cervical third of the roots. These professionals show compliance to the recommendations, which in turn is established by the fact that they have recognized the usefulness of the procedure in the detection of missed canals, in case of non-healing root canals, root fracture identification and pathologic conditions that are non-specific of endodontic origin (Tyndall and Kohltfarber 2012). Furthermore, the recommendations put forth in the position statement are also followed in using CBCT for the prognosis of root reabsorption lesions. Other studies also suggest that the use of CBCT is more common among dentists who perform teeth implantation (Tofangchiha et al. 2016). Thus, it can be suggested that the dentists accurately follow the criteria provided in the position statement. Furthermore, the AAE statements are also followed for assessing the anatomy of teeth that lie in close proximity to the apices of the root. Thus, adherence to the recommendations have made dental professionals accept the fact that this radiologic procedure.

References

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