Application of CBCT in the diagnosis of a cracked tooth – by Professor Gary S.P. Cheung

Radiography is an indispensable tool in any dental practice. Indeed, radiographic examination is invariably listed as one of the special investigation methods for nearly all oral and maxillofacial conditions. Conventional or film-based radiographic methods produce two-dimensional projections of the three-dimensional anatomical structures and require good knowledge of human anatomy for accurate interpretation.

The basics of CBCT

Computed tomography (CT) has revolutionised diagnostic imaging in that it provides a three-dimensional visualisation of the anatomical structures. Medical CT devices are typically supine gantry-style units that take up quite a lot of space in the radiology centres of hospitals. Yet, some oral and maxillofacial surgery (OMFS) clinics have resorted to such imaging method to visualise important structures that are situated in the operation field.

Today, with the advent of cone beam computed tomography (CBCT), 3D imaging has become possible in many dental practices. The dental specialities that most often utilise this imaging technique are perhaps OMFS, implant dentistry and endodontics. This short article aims to present some comments concerning the use of CBCT for the diagnosis of cracked tooth.

Two of the most often quoted and considered parameters of CBCT devices are field of view (FOV) and resolution. FOV refers to the volume of tissue in the patient’s head that is irradiated during exposure and, later, reconstructed in the computer as the region of interest (ROI). In general, the larger the FOV, the higher the radiation dose to the patient – hence, limited or small FOV scans are typically proposed by endodontists.

The resolution of a CBCT unit refers to its ability to show fine details. The smaller the size of a voxel, the smallest 3D element in volumetric analysis, the higher the image resolution [1]. Nowadays, most brands of CBCT scanners for dentistry manage an isotropic voxel size of 125 microns or better, with some devices achieving a voxel size of 75 microns.

The pros and cons of CBCT in the diagnosis of dental cracks

A cracked tooth has been a diagnostic challenge for many clinicians. Typically, the pulpal symptoms associated with the “cracked tooth syndrome” are poorly localised and may not be readily reproduced. A good knowledge of the symptomatology is of paramount importance in the diagnosis of dental cracks [2]. Then, visual examination under high magnification is also essential (Figure 1).

Figure 1. Clinical photos of a patient who complained about occasional, vague, dull, non-localised pain upon biting on the left side.

There is a clinical test, or a so-called wedge test, available, and it aims to reproduce the pain by applying stress to each suspect tooth, but that runs the risk of aggravating the extent of the crack. Conventional radiographs have limited value because of the projection geometry, that is, any crack lines not running in the same direction as the X-ray beam would become hidden and not detected in a periapical radiograph. If the offending tooth cannot be identified early, it may become fractured at a later date, rendering the tooth unrestorable. The possibility of detecting a crack and visualising its extension using a high-resolution CBCT device is highly appealing [3].

It is worth noting that the spatial resolution of CBCT scanners is about 75 microns under the best possible condition (i.e. in the absence of patient movement throughout the scan and with minimal interference or artefacts caused by metallic or radiopaque materials). That is, one should expect a realistic resolving power of about 100 microns, or 0.1 mm. If a “crack” should reach that width, it ought to be considered as a gap or fracture, with the crack line extending much further than the extent of that gap. In fact, the great majority of dental cracks can be detected under good lighting and magnification rather than by CBCT imaging (cf. Figures 1 and 2).
 

Figure 2. CBCT images of the same patient in Fig. 1 showing the left side of the jaws – top row: frontal plane showing the upper and lower first molar; bottom row: transverse plane at the level near the base of the occlusal fissures of tooth 16, with crosshair indicating the location of the section shown in the top row.

Conclusions

To the author, CBCT is not an appropriate tool for identifying the presence of a crack. Rather, it provides information that may indicate the development of some pathological reactions in response to the presence of a crack. Depending on the severity and extent of the crack, such responses may take the form of as follows:
a) Thickening of the sinus mucosa (see Figure 2) – which is not uncommonly seen for maxillary posterior tooth with apical periodontitis [4, 5]. 
b) Alveolar bone resorption – bony defects (Figure 3) may occur adjacent to dental cracks that had become infected and laden with bacteria.

Figure 3. CBCT images of a patient who had received the pulp revascularisation treatment of the lower left second premolar (tooth 35) for over 4 years, returned with history of one episode of pain after accidental biting on a hard object about a year before. Note the presence of localised alveolar bone defects at the buccal and lingual aspect of this 35, but the absence of discernible cracking of the root dentine in the transverse plane. The vertical root fracture of tooth 35 was diagnosed and, indeed, confirmed after extraction.

In summary, when a crack line is discernible on radiographs and/or CBCT images, treatment should include eradicating the fractured part of the tooth. In cases where some forms of biological response could be detected but a crack line is not visible in CBCT, meticulous examination under the operating microscope should be performed to rule out the presence of dental cracks, especially for patients with symptoms suggestive of cracked tooth.

Dr Gary S.P. Cheung, BDS, MDS, PhD, is the Clinical Professor in Endodontics and Associate Dean for the Undergraduate Education at the Faculty of Dentistry in the University of Hong Kong. He is the founder of the Hong Kong Endodontic Society, and he also serves as Supervisor of Training for the Specialty Board in Endodontics in Hong Kong. He has published over 40 papers in peer-reviewed journals, and has lectured extensively in Asia, Europe and the United States.

References

[1] Pauwels R, Beinsberger J, Stamatakis H, et al. (2012) Comparison of spatial and contrast resolution for cone-beam computed tomography scanners. Oral Surg Oral Med Oral Pathol Oral Radiol 114, 127–135.

[2] Cheung GSP (2014) Cracked tooth – a syndrome or conundrum? Hong Kong Medical Diary 19 (6), 13–16. (https://www.fmshk.org/database/hkmd/hkmd201406.pdf)

[3] Gao A, Cao D, Lin Z (2021) Diagnosis of cracked teeth using cone-beam computed tomography: literature review and clinical experience. Dentomaxillofacial Radiology 49, 20200407. (doi: 10.1259/dmfr.20200407)

[4] Matsumoto Y, Ikeda T, Yokoi H, Kohno N (2015) Association between odontogenic infections and unilateral sinus opacification. Auris Nasus Larynx 42, 288–293. (http://dx.doi.org/10.1016/j.anl.2014.12.006) 

[5] Gurhan C, Sener E, Mert A, Sen GB (2020) Evaluation of factors affecting the association between thickening of sinus mucosa and the presence of periapical lesions using cone beam CT. International Endodontic Journal 53, 1339–1347.