How CBCT is Changing Surgical Outcomes Assessment

By Chafic Safi, D.M.D., M.Sc., FRCD(C)

There is a consensus in endodontics that conventional two-dimensional (2D) periapical radiographs often present a challenge when it comes to their interpretation. The compressed three-dimensional (3D) structures on a 2D image along with projection geometry, superimposition of anatomic structures, distortion, and background noise account for the limitations of conventional periapical radiography. Therefore, interpreting 2D radiographs is often a subjective process and can lead to various opinions. In two important studies, Goldman et al. (1,2) showed that there was only 47% agreement among six examiners, two of which were endodontists, when evaluating healing of periapical lesions using 2D radiographs.  When the same examiners were asked to re-evaluate the films at two different time points, three examiners had only 72% to 88% agreement with their previous interpretations.  Considering that radiographic imaging constitutes a key component in our daily practice, it is clear that 2D imaging offers limited value when it comes to diagnosis, treatment planning, and outcome assessment.

On the other hand, Cone Beam Computed Tomography (CBCT) is a radiographic modality that has proven to be superior to 2D radiographs. Thanks to CBCT’s ability to accurately reproduce the periapical tissues and their three-dimensional relationship to anatomical landmarks, it is now gaining more popularity amongst endodontists. Several studies have shown that when compared to 2D radiographs, CBCT imaging has a higher sensitivity in detecting apical periodontitis (3,4,5). This has prompted The AAE and the AAOMR to issue an updated joint statement on the usage of CBCT in Endodontics. Nevertheless, CBCT is mainly used in the preoperative stages of conventional and especially surgical endodontics.

However, there are a number of recent studies suggesting that CBCT has an impact on surgical outcome assessment. Traditionally, surgical outcome assessment was based using the criteria defined by Rud et al.(7) and Molven et al. (8). In 2016, von Arx et.al (9) used these criteria to assess the treatment outcome one year after surgery using 2D and 3D imaging. The results showed a third of cases with persistent radiolucencies on CBCT. Since Rud’s and Molven’s criteria are based on 2D imaging, von Arx decided to redefine the CBCT criteria (10), based on Chen’s experimental dog study who correlated CBCT and histology results (11). These criteria showed that there are various healing rates according to the parameters observed, and that cortical bone was the slowest to heal. 5 years later, the same author re-assessed the same surgical cases using the same CBCT criteria, showing that there was a higher success rate when compared to the 1-year results, with cortical bone still lagging behind (12). These two studies did not compare CBCT to 2D radiographs, but still showed that CBCT surgical outcome assessment is not simple and that healing is a continuous process that can take up to 5 years.

Another set of surgical assessment criteria, the modified Penn 3D criteria, was established by Schloss et al. (13) and also based on the works of Chen et al (11). In their study, Schloss et al. compared surgical healing on 2D (Molven’s criteria) and 3D imaging after a mean follow-up period of 23.7 months, and also performed volumetric analysis of lesion size. They found that CBCT analysis was more precise than traditional 2D images in evaluating lesion size and healing with a significant difference.

Using Molven’s criteria and the Penn 3D criteria, Safi et al. showed in a randomized controlled trial that there was a substantial agreement between 2D and 3D surgical outcome assessment. However, their study had a mean follow-up period of 15 months when compared to 23.7 months in Schloss et al.’s study. This possibly suggests that differences in outcome assessment become apparent after a certain period, when comparing 2D and 3D imaging. Interestingly, they were also able to show that in some cases the cortical plate was healed but not the trabecular bone, challenging von Arx’s findings, and questioning healing kinetics and histological results of such cases, with possibility of scar tissue formation.

These findings, undoubtedly prove that CBCT imaging should not only be taught of in the preoperative stages of endodontics, but also in outcome assessment especially in the long-term surgical aspect of our field.

References

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14. Safi C, Kohli MR, Kratchman SI, Setzer FC, Karabucak B. Outcome of Endodontic Microsurgery Using Mineral Trioxide Aggregate or Root Repair Material as Root-end Filling Material: A Randomized Controlled Trial with Cone-beam Computed Tomographic Evaluation. J Endod 2019; 45: 831-9

Dr. Chafic Safi is adjunct assistant professor, University of Pennsylvania, Department of Endodontics.