Radiographic Interpretation

The[39] field of view (FOV) (Figs. 2-9 and 2-10) ranges from as small as a portion of a dental arch to an area as large as the entire head. The selection of the FOV depends on several factors. Among the most important are the following:
· Diagnostic task
· Type of patient
· Spatial resolution requirements
Neuropathic[44] orofacial pain or atypical odontalgia (AO), also known as chronic continuous dentoalveolar pain (CCDAP)131a and persistent idiopathic facial pain (PDAP),80a is related to a tooth, teeth, or pain at an extraction site where no clinical or radiographic pathosis is evident. Two systematic reviews of AO showed the incidence of persistent pain of more than 6 months’ duration after nonsurgical and surgical endodontic treatment, excluding local inflammatory causes, was 3.4%.130a The pathophysiology of this pain is uncertain, but it is hypothesized to involve deafferentation of peripheral sensory neurons in predisposed patients. The diagnosis of AO is challenging and depends on the patient history and clinical examination findings, in addition to the absence of radiographic findings. In some cases the symptoms from AP and AO are closely related. Pigg et al.146a conducted a study of 20 patients with AO. All of the patients had at least one tooth in the region of discomfort that had undergone invasive treatment; 21 of 30 teeth had undergone endodontic treatment. These researchers found that 60% had no periapical lesions, and among those who did, CBCT showed 17% more periapical lesions than conventional radiography. This study demonstrated that CBCT may be a useful supplement to 2D radiography (see Fig. 2-15).
Diagnosis[44] of Endodontic Treatment Failures
Failure of previous endodontic therapy can be attributed to various factors, such as procedural errors, missed canals, or persistent periapical pathosis. Knowledge of the cause of failure is pertinent to the treatment of these cases because it allows the cause to be adequately rectified. With the advent of CBCT, in select cases of retreatment in which the cause of failure is otherwise undetectable, adequate information may be collected to apply to the treatment plan (Fig. 2-16). The technology is most useful in detecting uninstrumented and unfiled canals,[45] extension of the root canal filling, and the presence and extent of periradicular bone loss. The sensitivity of CBCT and PA radiographs for diagnosing strip perforations in root-filled teeth has been shown to be low.51 Radiopaque filling materials in the root canals of endodontically treated teeth can produce streak artifacts, which can mimic fracture lines or perforations.166,198
Vertical[45] Root Fractures
Vertical root fractures (VRFs) that run along the long axis of a tooth are often difficult to diagnose clinically. The prevalence of VRF in endodontically treated teeth has been reported to range from 8.8% to 13.4%.61,174.196 These fractures typically run in the buccolingual direction and are confined to the roots, making it difficult to visualize the fracture. Visualizing the fracture on a conventional radiograph is possible when the x-ray beam is parallel to the plane of the fracture.153 Challenges in diagnosis with regard to the extent and exact location of the fracture often lead to unwarranted extraction of teeth. Since the introduction of CBCT to dentistry, various reports of the application of the technology to detect vertical root fractures have been published. The reported sensitivity for detection of VRFs has ranged from 18.8% to 100%115; by comparison, conventional radiographs have a reported sensitivity of approximately 37%48,75 (Fig. 2-17). CBCT has been used to visualize VRFs in controlled clinical studies in which clinical diagnosis was difficult.48 Vertical root fractures were successfully detected at a spatial resolution ranging from 76 to 140 microns. However, only a limited number of units provide such high resolution. A comparison of various CBCT units for the detection of VRFs demonstrated that the units with flat panel detectors (FPDs) were superior to the image intensifier tube/charge-coupled device (IIT/CCD)–based detectors; the smaller FOV and the ability to view axial slices also improved detection of VRFs.76 Continued improvement of sensor technology, including the use of FPDs, has resulted in enhanced resolution. Voxel dimensions are smaller in these units. Detection of vertical root fractures with thickness ranging from 0.2 to 0.4 mm was found to be more accurate with CBCT than with digital radiography.133,138 The presence of root canal filling in the teeth lowers the specificity of CBCT in detecting vertical root fractures75,76,95; this has been attributed to the radiopaque material causing streak artifacts that mimic fracture lines.198
The[48] accidental introduction of root canal instruments, irrigating solutions, obturation material, and root tips into the maxillary sinus has been reported. Serious consequences associated with the intrusion of foreign bodies into the maxillary sinus include pain, paresthesia, and aspergillosis, a rare but well-documented complication of endodontic treatment.16a Guivarc’h et al.71a reported that the overextension of heavy metal–containing root canal sealers, such as zinc oxide eugenol cement, may promote fungal infection in immunocompromised patients, leading to bone destruction and damage to adjacent structures. This case report described the use of computed tomography to assess the patient before surgery and at 6 months.71a The use of CBCT as an aid in the localization and retrieval of an extreme overextension of thermoplasticized injectable gutta-percha into the sinus and contiguous soft tissues has been described by Brooks and Kleinman.26
Calcified[49] Canals
According to the Pew Research Center, 10,000 U.S. individuals will reach the age of 65 every day until 2030, and the nation’s 65-year-old and over cohort will grow to 81 million in 2050, up from 37 million in 2005 (also see Chapter 26).82 This aging population will present increasing challenges for dental clinicians because calcification of the root canal system increases as part of the natural aging process,69 possibly leading to more untreated canals that may serve as a niche for microorganisms.19,88 Pulp chambers in the crown of the tooth decrease in size, forming more rapidly on the roof and floor of posterior teeth.184 Typically, root canals calcify at the coronal aspect first, with decreasing calcification as the canal travels apically. Magnification and illumination are essential tools for the identification and treatment of calcified canals, but CBCT can assist in the perioperative treatment of such conditions.16 Preoperative assessment of calcified teeth using CBCT can suggest the best tactic for locating calcified canals in the chamber floor and roots[50] using software-based measurement tools. The insertion of radiopaque markers, such as instruments or obturation material, can facilitate reliable canal localization using available multiplanar reformations. The increased sensitivity and specificity provided by CBCT can also assist in the determination of the periapical status of calcified root canals that may not require measures that can lead to procedural errors, such as off-course access, instrumental fracture, or root perforation.83 The difficulty in locating calcified canals can be further compounded by morphologic anomalies associated with gender and ethnic origin.163 CBCT can be an important adjunct to magnification and illumination in these cases.
Although[54] the literature describes many classification systems, this section divides inflammatory root resorption into two groups, according to location: internal root resorption (IRR) and external root resorption (ERR).177 IRR is a relatively rare occurrence that is usually detected on routine diagnostic PA or panoramic radiographs.102,139 It is characterized by structural changes in the tooth that appear as oval or round radiolucent enlargements of the pulp canal, usually with smooth, well-defined margins.32 IRR is usually asymptomatic, associated with pulpal necrosis coronal to the resorptive lesion and vital or partially vital pulps where active.140 These lesions can easily be confused with extracanal invasive cervical resorption because the radiographic appearance of the two lesions can be identical. CBCT is helpful for diagnosing the location and exact size of IRR. In a study by Estrela et al.,52 48 PA radiographs and CBCT scans were exposed on 40 individuals.52 IRR was detected in 68.8% of PA radiographs, whereas CBCT scans showed 100% of the lesions. Conventional radiographs were able to detect only lesions between 1 and 4 mm in 52.1% of the images, whereas CBCT was able to show 95.8% of the lesions. This finding was in agreement with other studies that demonstrated the value of tomographic analysis.36,105 In a study by Kim et al.,92 the extent and location of the IRR was accurately reproduced with the fabrication of a rapid prototyping tooth model. Although relatively few systematic studies on artificially induced IRR have been reported because of the difficulty in creating such defects, Kamburoglu and Kursun90 concluded that high-resolution CBCT imaging in detecting simulated small internal resorptive lesions.
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