Tomography in endodontics. 1st part. Online class on the Carlos Ferrari Endodontics channel on youtube.
In: Carlos Ferrari et al. Chap. Radiology in Endodontics. Ricardo Machado. Endodontics. Princípios Técnicosose Biológicos. Ed. Gen, 2022:
Computed Tomography in Endodontics
Despite the applicability of radiographic examination in the different phases of endodontic treatment or retreatment (conventional and surgical), its limitations must be considered. The advent of computed tomography has provided important advances to different dental specialties, especially due to the three-dimensionality of the images obtained. However, the high cost, difficult access and low resolution of the images still represented an impediment to their use in clinical routine.
The development of Cone-Beam Computed Tomography (CBCT) provided greater accessibility to the exam due to the reduction of costs previously practiced, lower doses of radiation and higher quality images. In Endodontics, its use became popular with the emergence of devices with even more accurate resolution and images with better detail and clarity. Therefore, there is a tendency for CBCT to be used for all cases from diagnosis to proservation.
CBCT has numerous advantages, such as three-dimensional visualization, no overlaps, observation in multiple planes, and dimensional fidelity, as well as facilitating communication between professional and patient, and between professionals.
However, the exam has relevant disadvantages, such as the cost, still relatively high compared to the radiographic exam, and the production of image artifacts (interferences caused by the presence of metal). These disadvantages tend to decrease with time, with the popularization of the exams and the development of new technologies and software.
General concepts
Voxel and FOV
The smallest unit of a three-dimensional image and therefore used in tomography is called a voxel, which has three dimensions and a cubic shape. The smaller the voxel of an image, the better the definition. Therefore, for Endodontics, the ideal is that the images are formed by the smallest voxel units. The FOV (field of view) refers to the size of the area that will be exposed and will be part of the examination. For Endodontics, the FOV can be from about 4 × 4 cm, in order to encompass the tooth to be studied and the adjacent region.
Image acquisition
In CBCT, there is an X-ray beam in a conical format that, when rotated around the patient, produces a series of images that will be grouped by the software, later giving rise to a three-dimensional image of the area studied. This image is then processed to constitute the slices and reconstructions. The images obtained are classified as hypodense, isodense, and hyperdense, according to their density, similarly to the radiolucent, neutral, and radiopaque images used in radiographs.
Cuts and reconstructions
After image acquisition to obtain a single three-dimensional image, one can investigate the area/tooth in different planes, using filters and other graphic resources. The basic cuts are sagittal, coronal and axial, the latter being the most relevant for endodontic diagnosis. In addition, cross-sections can be performed in any plane and direction.
Using image processing software, it is also possible to do a panoramic reconstruction, which can have the thickness and capture area of the image customized. A full panoramic reconstruction (upper and lower arches) is similar to a normal panoramic radiograph, but without overlaps.
Another important reconstruction is 3D, in which a three-dimensional model of the captured area is produced, with numerous possibilities for treatment, colorization, density change, and slicing. In addition, 3D models can be printed, for diagnostic and surgical planning.
In summary, the most commonly used tomographic images in Endodontics are those provided from axial and cross-sections, and 3D reconstructions.
Applications of Cone-Beam Computed Tomography in Endodontics
CBCT can be used in all phases of endodontic treatment or retreatment, from diagnosis to proservation. A CT scan is able to provide significantly more information than a periapical radiograph. Therefore, it justifies the fact that in 30 to 60% of cases there is a change in diagnosis or planning when a professional evaluates a periapical radiograph and a CBCT of the same tooth or area.
CBCT is useful for the three-dimensional analysis of dental morphology, revealing much more accurately the dimensions of the pulp chamber, the quantity and characteristics of the root canals. In retreatments, it is of utmost importance in the detection of untreated canals, deviations, perforations, etc.
CBCT can also be used to detect cracks or root fractures. However, the line confirming this hypothesis is not always observed, making clinical and/or surgical prospection necessary. In these cases, a major obstacle to diagnosis lies in the occurrence of image artifacts, producing hypodense and hyperdense lines, most often observed in teeth with metal intraradicular retainers
In cases of root resorption, CBCT comprises a much more effective means than radiographic examination for its diagnosis. Moreover, only a three-dimensional examination can identify the occurrence of communications between a resorption and the root canal and between the root canal and periodontal tissues (external and internal resorption, respectively).
CBCT is more accurate in identifying hypodense images compared to radiographic examination42. Therefore, it is a more reliable exam in the detection of early stage periapical lesions, in the establishment of differential diagnosis between lesions of endodontic and non-endodontic origin, in surgical planning and in proservation. CBCT reveals images in the periapical region earlier, at stages not yet observable on periapical radiographs, and with greater possibility of detection. In cases of larger images, there is no consensus in the literature that CBCT can be a reliable method to differentiate between cysts and periapical granulomas.
When hypodense images are located in the maxillary posterior teeth, CBCT can be instrumental in the differential diagnosis of odontogenic sinusitis by revealing the communication of lesions with the maxillary sinus, cortical disruption, and thickening of adjacent mucosa.36 This condition is common and underdiagnosed by both dentists and physicians.
CBCT can also be used to analyze the proximity of root apices to important anatomical structures, such as the maxillary sinus and mandibular canal. In addition, it allows for the prior observation of apical fenestrations, which can also be useful for the diagnosis of long-term postoperative pain with no apparent cause.
In dental trauma, CBCT is useful to reveal crown and/or root and bone fractures as well as to identify voids within the alveolus. CT scanning has proven to be appreciably more efficient than panoramic radiographs in identifying bone and alveolar fractures and than digital periapical radiographs in detecting horizontal root fractures, even with different angulations.
In cases of teeth with pulp chamber and root canal atrophic by mineralization - a common situation in traumatized anterior teeth - CBCT, combined with prototyping technology, can be used by means of guides made in 3D printers, to guide the access of a surgical drill to the periapical region. This treatment is called guided endodontic access. For more details, we recommend reading the Chapter, CAD/CAM Guided Endodontics (Endoguide 3D).
CT scanning can also be used for the diagnosis of foreign bodies, fractured instruments, perforations, overburation, and overextension.
tomography in endodontics
