CBCT technology: How has it impacted clinical endodontic care?

As a partial disclaimer, I am an enthusiastic early adopter of CBCT imaging in endodontics and believe the benefits far outweigh any additional costs and potential risks. I also acknowledge that high-level clinical evidence to support this enthusiasm is currently lacking, although case series studies¹ and clinical experience have shown that CBCT imaging, when compared to standard 2-dimensional (2D) imaging, allows for greater accuracy in diagnosis and treatment planning and has the potential to enhance patient safety. The addition of CBCT to the patient's history and standard clinical tests and examinations allows clinicians to better inform their patients of treatment benefits, risks, alternatives, and prognoses. It also can result in the avoidance of treatment when the additional information gained by a CBCT scan indicates that extraction may be the preferred option.

Limited field of view (FOV) CBCT (< 8 cm) is most commonly used in endodontics and provides higher resolution (smaller voxel size), reduced scatter radiation and noise, and lower radiation exposure compared to full-arch and full-jaw CBCT.² Radiation exposure from a typical limited FOV CBCT is approximately 47 µSv, or roughly equivalent to6 days of normal background radiation.

In July 2015, an updated joint position statement by the American Association of Endodontists (AAE) and the American Academy of Oral and Maxillofacial Radiology (AAOMR) was released³ (a minor update was issued in 2016). The most salient parts of the position statement are summarized as follows: “Limited FOV CBCT should be considered the imaging modality of choice” for initial treatment of teeth with the potential for extra canals and/or complex anatomy (potentially including almost all teeth except some maxillary anterior teeth), diagnosis in patients with contradictory or nonspecific clinical signs and symptoms, intra-appointment identification of calcified canals, detection of vertical root fractures when 2D imaging is nonconclusive, evaluation of incomplete healing and the possible need for nonsurgical or surgical retreatment, treatment planning for microsurgical endodontic treatment and implant placement, and the diagnosis and treatment of minor dentoalveolar trauma and resorptive defects. Recent research has suggested that diagnostic accuracy may be significantly improved when using CBCT compared to traditional 2D imaging and that the final treatment plan may change in up to 50% of cases when CBCT is used.^4,5

Limitations and caveats include the potential for imaging artifacts, especially in the vicinity of radiopaque materials such as gutta percha and metallic restorations; cost of equipment; need for additional training and experience to properly interpret CBCT scans; and current lack of solid evidence to support the position that routine use of CBCT in endodontics leads to improved treatment outcomes. This final caveat, however, is true of any new technology and is not a reason to reject it but, rather, to proceed with an open mind and remain current with the best evidence as it becomes available.

The greatest impact of CBCT imaging in clinical endodontics has been in the area of diagnosis. However, because diagnosis and treatment planning are clinically intertwined, the effect of this imaging modality can be extended to both diagnosis and treatment planning during endodontic care. The primary etiology of endodontic disease is known to be microbial contamination of the periapex through the root canal space; therefore, identification and disinfection of all root canals and associated spaces is paramount in providing the highest possible chance of success during clinical care.

Missed root canals are a major cause of endodontic failure. Thus, identifying the location of all canals prior to treatment or discovering any missed canals in failed cases can improve prognosis and treatment planning before or after primary treatment. This is where 3-dimensional (3D) CBCT imaging truly shines compared to standard 2D periapical radiographs. Although standard periapical imaging remains the primary diagnostic tool in endodontics, it cannot provide information regarding overlapping roots and additional canal anatomy in some cases. An axial section through such teeth via CBCT imaging can allow the clinician to determine whether aberrant anatomy exists and where it can be found during the access procedure. This information can help improve both the efficacy and efficiency of access and instrumentation. Knowing in advance that additional anatomy does not exist can help reduce exploration time, while foreknowledge of the location of additional canals can help clinicians target their search and reduce unnecessary dentin removal.

Furthermore, CBCT imaging is useful in locating the position and extent of resorptive lesions and some dystrophic calcifications and aids clinicians in determining treatment strategies in such cases. This imaging also can help clinicians determine the presence of possible perforations and other procedural errors in previously initiated treatment while assisting in treatment planning these cases for more predictable outcomes.

Another benefit of this imaging modality is in the treatment planning of failed initial treatment and triage of cases for a surgical versus a nonsurgical approach through better assessment of the source of failure. For example, incomplete cleaning and shaping or missed root canals are best retreated nonsurgically, whereas a surgical approach may be recommended when canals appear adequately obturated but unyielding coronal obstructions are present. Additionally, in cases in which surgical treatment is chosen, information gathered from assessment of the significant jaw anatomy, such as the location of the inferior alveolar nerve, mental nerve, and maxillary sinus, as well as the depth and distance to roots from the buccal alveolar plate, can be critical to the surgeon for optimal treatment planning and safer outcomes.

However, although supplementary knowledge is always more helpful than not in diagnosis and treatment planning, financial considerations and the additional radiation exposure for this diagnostic imaging modality have precluded it from being a panacea like conventional periapical radiographs for all clinical cases. The recent joint position statement by the AAE and AAOMR³ in 2015 provides recommendations to help define proper use of this imaging modality during clinical care, and it should be referred to for a more in-depth understanding of the indications of use of CBCT imaging in endodontics.

The late Dr. Morton Amsterdam, the first chairman of a graduate program in endodontics and considered to be the “father of periodontal prosthesis,” said, “There are many ways to treat a disease, but only one correct diagnosis.” Sometimes clinicians need everything available to them to make that diagnosis. Dental medicine technology has developed enormously over the years, and one device that contributes to diagnosis, interpretation, and delivery of care is the cone beam.

CBCT has been a growing part of the endodontist's armamentarium. During a scan, the CBCT machine rotates around the patient, capturing images using a cone-shaped x-ray beam. A 3D representation is then created utilizing computer software. In endodontics, a limited FOV CBCT allows the imaging to be directed only at the area of interest and not the surrounding tissues. The smaller FOV provides higher resolution with less radiation exposure. Because the FOV is smaller, the voxel size can be reduced to aid in image clarity (0.076 mm to 0.2 mm versus 0.3 mm to 0.4 mm).

CBCT, however, is not the standard of care and should not be used routinely for endodontic diagnosis or screening purposes in the absence of clinical signs and symptoms. One concern, in particular, is overexposure to children. The Image Gently Campaign (imagegently.org) has raised awareness to lower radiation in imaging children.

Nevertheless, CBCT does have a place in endodontic diagnosis with complex cases. The AAE in association with the AAOMR published a joint position paper on CBCT usage in endodontics,³ and their recommendations include the following:

1. Endodontic diagnosis—The use of CBCT imaging must be consistent with ALARA principles (as low as reasonably achievable). Because the ionizing radiation dosage for CBCT imaging is higher than for traditional intraoral radiographs, clinicians need to consider the cumulative radiation exposure over a patient's lifetime. In some situations, when planar views are inconclusive, the addition of CBCT imaging might add value to the diagnosis. Examples of such cases include contradictory or nonspecific signs and symptoms associated with untreated and previously treated teeth, complex morphology, calcified canal location, and evaluation of non-healing lesions.

2. Initial treatment—CBCT imaging should be considered on teeth that have the potential for extra canals and complex morphology. Also, CBCT can aid in finding calcified canals. For immediate postoperative imaging, intraoral radiographs should be used.

3. Nonsurgical retreatment—If 2D images and the clinical examination are inconclusive in detecting vertical root fractures (VRFs), CBCT imaging should be considered. However, because of known artifacts that occur on previously root-filled teeth (eg, beam hardening), the clinician must maintain a high level of uncertainty in diagnosing a VRF based on the CBCT. Furthermore, CBCT imaging can be helpful for evaluating non-healing previous endodontic treatment and for developing any needed additional treatment, including nonsurgical, surgical, or extraction.

4. Surgical retreatment—CBCT should be considered the imaging modality of choice for presurgical treatment planning to localize root apex/apices and evaluate proximity to adjacent anatomical structures (eg, mental foramen, inferior alveolar bundle, sinus).

5. Special conditions—CBCT should be considered the imaging modality of choice to best evaluate the degree and severity of dentoalveolar trauma, alveolar fractures, luxations, root fractures, or displacement of teeth. In addition, differentiating between external versus internal root resorption can best be done with CBCT imaging, and its proximity to alveolar bone can be determined, to help formulate a restorative prognosis. CBCT imaging should be considered when implant placement is an option.

6. Outcomes assessment—Intraoral radiographs should still be used to evaluate postoperative healing after nonsurgical and surgical endodontic treatment.

CBCT imaging is revolutionizing endodontic care for patients. While an experienced diagnostician with the aid of a parallel and clear 2D radiographic image can correctly diagnose and treatment plan most endodontic problems, CBCT adds a third dimension and offers significant benefits that can accelerate clinicians' understanding of endodontic problems. Dr. Amsterdam was correct; we need to make a correct diagnosis. Treatment after that may proceed along different paths.

Bradford R. Johnson, DDS, MHPE

Professor and Department Head, Department of Endodontics, University of Illinois at Chicago, Chicago, Illinois; Diplomate, American Board of Endodontics

Allen Ali Nasseh, DDS, MMSc

Clinical Instructor, Department of Restorative Dentistry and Biomaterial Sciences, Harvard University School of Dental Medicine, Boston, Massachusetts; President, RealWorldEndo™,
 Wilmington, Delaware; Private Practice, Boston, Massachusetts

Louis E. Rossman, DMD

Past President, Foundation for Endodontics, Chicago, Illinois; Diplomate, American Board of Endodontics; Private Practice, Philadelphia, Pennsylvania