In this chapter, the main uses of cone-beam computed tomography (CBCT) in endodontics are discussed in light of some of the most recently published literature. There is no doubt that CBCT use in dentistry is increasing due to its advantages compared to other radiographic imaging techniques; however, it comes at the expense of increased exposure to ionising radiation. Its use should follow sound principles and have the potential to improve the diagnosis and positively impact the decision-making process of the clinician.
The use of radiographic methods is an essential part of endodontics. It is well established that conventional two-dimensional radiographic techniques have limitations in terms of diagnostic yield, due to factors such as anatomical noise  and geometric distortion . Cone beam computed tomography (CBCT) has been increasingly used worldwide as a three-dimensional imaging technique that overcomes most of the shortcomings of conventional radiographs, particularly in complex cases .
27.2 Detection of Apical Periodontitis
Well-designed ex vivo human as well as animal studies with reference standards have concluded that CBCT is more accurate than periapical radiographs (PR) in detecting apical periodontitis [6–8] as CBCT is known to overcome many of the limitations of two-dimensional PR .
Root canal treatment of teeth with preoperative radiographic signs of apical periodontitis (AP) has been shown to have lower radiographic success rates when compared to teeth with no signs of AP . Subtle or ‘hidden’ periapical changes that may otherwise be missed or impossible to visualise using PR can be detected using CBCT examinations (Figure 27.1), which has the potential to result in earlier diagnosis and treatment of endodontic disease or advise against inappropriate treatment decisions [11, 12].
Kruse et al.  used histopathology as a reference standard in cadavers to show that the diagnostic accuracy of CBCT depends on the treatment status of the tooth. In non-root filled teeth, the diagnostic accuracy is higher than in root filled teeth, nevertheless it was high in all instances. The radiographic appearance of the periodontal ligament can be variable when assessed with CBCT , particularly when compared to PR , and there is a risk of ‘overdiagnosis’ of AP. It has been suggested that the clinician’s ability to interpret and diagnose correctly AP on CBCT scans is dependent on their experience  and therefore appropriate training is essential [16, 17].
27.3 Root Canal Anatomy
Clinicians can underestimate the true complexity of root canal anatomy when evaluating radiographic images because of the two-dimensional nature of PR and the associated radiographic ‘anatomical noise’ [19–21] as well as the inherent population  and age-related changes .
CBCT has been shown to be more accurate than PR for detecting fine root canal anatomy such as the presence of additional roots  or the presence of unusual anatomical variations in terms of root canal morphology [25, 26]. It has been highlighted that specialist endodontists failed to identify the presence of additional root canals in up to 41% of cases when using PR as compared to CBCT ; similarly, a significant proportion of second mesio-buccal (MB2) canals were identified with the adjunct of CBCT as compared to PR alone .
CBCT is almost ubiquitously indicated in cases with aberrant anatomy such as dens invaginatus [18, 27, 28] or germinated or fused teeth . The additional information gained from a CBCT in these situations informs the clinician as to the number, position, and likely obstacles that may be encountered during treatment (Figure 27.2). Owing to the increased use of three-dimensional imaging in research (such as micro-CT and CBCT) as well as clinical CBCT and improved awareness of the wide range of anatomical variations in the human dentition, a new system for classifying the root and canal morphology as well as dental anomalies have been introduced [30, 31].
A contemporary and novel indication for the use of CBCT allows for the combination of 3D optical scans as well as CBCT data sets to fabricate endodontic stents with guide sleeves to facilitate guided endodontic access cavity preparation in teeth diagnosed with pulp canal obliteration  and three-dimensional navigation in endodontic microsurgery . The purported benefits include conservative access cavity preparation, reduced technique sensitivity, decreased chair time, as well as a less iatrogenic damage [34, 35]. These data sets have been used with software packages such as 3D EndoTM (Dentsply Sirona, York, PA, USA) to improve treatment planning and reduce stress levels of clinicians because they provide a user-friendly interface that allows the clear visualization and measurements of the root canals, as well as prediction of potential areas of risk .
27.4 Root Canal Retreatment
The underlying shortcomings and cause of post-treatment disease following root canal treatment may not be readily assessed with periapical radiographs. CBCT scans are more likely to detect untreated root canal anatomy, perforations, voids, or incomplete root canal fillings (Figure 27.3), all of which may have a negative impact on the outcome of the primary treatment [37, 38]. Careful interpretation and a good understanding of the limitations of CBCT scans are mandatory, particularly in root filled teeth because the appearance of artefacts caused by beam hardening can be mistakenly diagnosed as missed canals, voids, or even vertical root fractures [39, 40].
The additional information collected from a CBCT scan has been shown to have an impact on the decision-making process and treatment planning in cases of persistent disease [41, 42]. Rodriguez et al. [43, 44] demonstrated that the treatment modalities were influenced not only amongst general dental practitioners but also specialists when CBCT was used, particularly in cases with greater complexity.
27.5 Endodontic Surgery
CBCT has been recommended as a useful diagnostic tool for treatment planning in endodontic surgery [45–47]. It provides a more precise method of determination of the spatial distribution and relationship of periapical lesions of teeth with persistent disease and surrounding structures . Additionally, it allows the correct identification of missed anatomy (Figure 27.4) , influencing the diagnosis and treatment planning  and potentially improving the outcome of treatment .
In multi-rooted teeth, the surgical approach may be individualised to the root affected by AP, thus facilitating the surgical procedure , reducing the treatment time, and improving outcomes . The amount and accuracy of information provided by CBCT cannot be matched by that obtained with PRs. CBCT can be used as a precise measuring tool of root dimensions [53, 54], distance, and identification of important anatomical structures such as the mandibular canal, mental foramen, or the maxillary sinus [55, 56]; cortical and cancellous bone thickness ; position and presence of bone defects ; orientation of the long axis of the root of the tooth in relation to the cortical plate to aid correct bur depth and orientation ; and identification of isthmi  and other anomalous tooth anatomy [28, 58, 59]. Most of this information cannot be obtained with PR.
27.6 Dental Trauma
Plain film radiography (PRs as well as horizontal and vertical parallax radiography) are recommended for the assessment and diagnosis of traumatic dental injuries (TDI) . However, because of inherent limitations of PR, significant signs and/or injuries following a TDI may be overlooked [51, 64].
The benefits of using CBCT in localised dento-alveolar trauma include the ability to accurately diagnose and plan an appropriate intervention (if needed) based on a single small volume CBCT examination [65, 66]. It is also possible for the clinician to examine the associated soft tissues for the presence of any foreign bodies that may have been displaced during the trauma.
CBCT examination following TDI has been shown to provide greater objective examination and assessment (Figure 27.5) of the dental hard tissue [65–67] and the associated periodontium [66, 68, 69]. Furthermore, CBCT investigation has also been proven to be more sensitive to the detection of alveolar bone fractures when compared to PR [70, 71].
Patient psychology, particularly in younger patients following a TDI, can be one of the factors that render the intraoral PR rather difficult and/or too uncomfortable to perform effectively. The extraoral CBCT is more amenable from a patient comfort point of view as well as potentially reduces the radiation exposure since several PR images with different projections are usually required in addition to occlusal radiographic images. Furthermore, ‘late’ complications occurring following a TDI, such as resorptive pathosis or apical periodontitis, can be detected at an earlier stage and as such, treatment may be initiated .
CBCT should be considered for the diagnosis, management, and follow-up of localised complex TDIs as a result of the superior ability of CBCT to examine as well as identify any significant early or late pathosis associated with a TDI.
27.7 Diagnosis and Management of Root Resorption
Resorptive lesions that extend in the buccopalatal plane can only be precisely assessed with CBCT (Figure 27.6), which may be particularly relevant to investigate the presence of perforations . The prognosis of the various treatment modalities may be dependent on this information [76, 77]. Benchtop studies have demonstrated the increased level of accuracy of CBCT for detecting internal  and external root resorption [72, 79, 80].
The clinical implications of the increased accuracy and additional information obtained by CBCT imaging when compared to PR resulted in more appropriate treatment decisions for the management of root resorption as demonstrated by Patel et al.  and corroborated by other clinical studies [41, 43, 44, 82].
Inflammatory root resorption is more readily detectable when CBCT is used when compared with PR . The full extension and true nature of external cervical resorption (ECR) is difficult to appreciate using PR alone [84, 85]. These resorptive lacunae may have varying radiographic features due to different spread within the tooth, location, and relative content of fibrovascular and/or bone-like tissue . These features are more discernible when CBCT (Figure 27.6) is used, which have an impact on treatment planning . The previous two-dimensional Heithersay  classification does not clearly differentiate the circumferential spread and potential pulpal involvement of ECR defects. When this classification was used in both simulated ECR lesions  and in a clinical study , it was concluded that the Heithersay classification was not accurate for detecting ECR. Furthermore, PR fared worse than CBCT in terms of accuracy of location and circumferential spread, which ultimately resulted in poorer treatment options when PR alone was used. A three-dimensional classification was introduced by Patel et al.  to describe ECR using the additional information gained from CBCT scans. The importance of CBCT in the management of ECR has been highlighted in the European Society of Endodontology’s position statement on external cervical resorption .