Condylar position on cone-beam computed tomography images and its correlation with condylar size on panoramic radiographs

Introduction

Temporo-mandibular joint (TMJ) is a complex synovial joint located between the condylar head and mandi­bular fossa of the temporal bone at the base of the skull. TMJs are located bilaterally and operate simultaneously, connecting the mandible to the skull. Anatomical components of TMJ include the mandibular condyle, mandi­bular fossa, articular eminence of the temporal bone, soft tissue components of the articular disc, attachments, and articular space [1, 2]. Morphological changes or asymmetry of TMJs may occur due to the effect of parameters, such as a missing tooth, mechanical wear, premature contacts, parafunctional habits, unilateral cross-bite, and dento-skeletal discrepancies [3]. Factors, such as age, gender, occlusal and muscular forces, facial growth pattern, pathological conditions, class II malocclusion with asymmetry, temporo-mandibular disorders, and outcomes of some faulty orthodontic and prosthodontic treatments, may also alter the morphology and function of TMJ. Such changes often lead to morphological compensation of TMJ [4].
Commonly used imaging modalities for evaluation of TMJ comprise panoramic, submentovertex, trans-cranial, trans-pharyngeal, and cephalometric radiography, conventional tomography, computed tomography (CT), and magnetic resonance imaging (MRI). More recent radiographic modalities include volumetric CT or cone-beam computed tomography (CBCT), sonography, and three-dimensional reconstructions [5].
Bi-dimensional imaging has limitations compared with tri-dimensional imaging. Bi-dimensional images cannot offer a comprehensive view of TMJ structures in all three planes, resulting in an incomplete or distorted representation, particularly when assessing condyle’s morphology or TMJ’ spatial relationships. Tri-dimensional imaging overcomes these constraints by providing a holistic, three-dimensional representation, allowing for more accurate assessments and diagnoses [6, 7].
Panoramic radiography provides a comprehensive two-dimensional (2D) view of the jaws; however, lower image quality compared with intra-oral radiography, dependence on the operator, and geometric image distortion, e.g., magnification and unequal elongation, are among its drawbacks. CBCT has several advantages over medical CT, such as lower cost, smaller size of equipment, and lower radiation dose. It is also more easily available for dento-maxillofacial examinations. However, poor soft tissue contrast is a major drawback of CBCT [8].
Previous studies assessed the TMJ morphology and related influential factors using cephalograms and pano­ramic radiographs, which are non-specific for condylar assessment. Exclusive imaging modalities for TMJ include the trans-cranial and trans-pharyngeal radiography. However, in these imaging modalities, the technician has to adjust the head position, which may cause dimensional and morphological errors in an assessment of TMJ. However, technical errors can be omitted in CBCT by using a software.
Panoramic radiography is commonly requested by dental clinicians. Mandibular condyles can be assessed on panoramic radiographs to some extent. However, the angulation of condylar head on the condylar neck can affect condylar morphology and cause errors in correct estimation of the shape and size of condyles on pano­ramic radiographs. For instance, in a patient with TMJ pain due to temporo-mandibular disorder, such errors can lead to misdiagnosis if dental clinician is not aware of the effect of deviation and rotation of the condylar head on the condylar neck and its size, and may mistakenly attribute the pain to false asymmetry of the size of right and left condyles or false hypoplasia of one condyle; whereas, condyles usually have the same size in majority of individuals, and it is the rotation of condylar head at one side that makes it appear smaller than contralateral condyle on panoramic images. However, this error can be detected on CBCT scans. Panoramic radiography does not allow evaluation of the angle of rotation of condylar head on the condylar neck. However, this angle can be calculated on CBCT axial sections.

Objectives

This study aimed to assess the condylar position on CBCT images and its correlation with the apparent condylar size on panoramic radiographs.

Material and methods

This cross-sectional study was conducted among 32 patients presenting to the Radiology Department of School of Dentistry, Tabriz University of Medical Sciences between 2021 and 2022 who required both pano­ramic radiography and CBCT for diagnostic purposes not related to this study (such as dental implant placement). The study protocol was approved by the Ethics Committee of Tabriz University of Medical Sciences.

Eligibility criteria

Patients aged between 20 and 80 years who required both CBCT and panoramic radiography, and presented with equal size of the right and left condyles on CBCT scans were enrolled. Exclusion criteria were history of surgery or fracture of the jaw or TMJ, congenital anomalies of TMJ, pathological lesions of the jaw, faulty restorations, complete or partial denture, complete edentulism, history of systemic diseases, and taking medications affecting the joints.

Sample size

A pilot study was conducted to calculate the sample size. Accordingly, regression coefficient for the ratio of the size of condylar head on panoramic radiograph/ the size of condylar head on CBCT scan was found to be 4.46. Also, standard deviation of the size of condylar head on panoramic radiograph and CBCT scan was found to be 0.98 and 7.91, respectively. Considering a study power of 90% and type I error of 0.05, the sample size was calculated to be 26. To increase reliability of findings, the sample size was increased by 20%, and 32 samples were evaluated.

Methodology

Written informed consent was obtained from participants to use their radiographs for research purposes. All CBCT scans were obtained with NewTom VGi CBCT scanner (QR Verona, Italy), with a flat-panel detector, 1,536 × 1,920 pixel resolution, 127 x 127 µm2 voxel size, 14-bit depth, 360-degree rotation, 18-second scanning time, and maximum voltage of 110 kVp. Initial and final reconstruction of images were carried out using NNT Viewer version 8.0.0. Exposure parameters were adjusted automatically. CBCT images were viewed on a 19-inch LCD monitor (190B; Philips) with 1,024 × 1,208 pixel resolution and 32-bit depth in a semi-dark room by an oral and maxillofacial radiologist and a senior dental student. Head position was standardized in the software, and slice interval for axial sections was selected to be 0.3 mm. On coronal view, constriction rectangle was parallelized to supra-orbital ridge. On axial section, scroll bar was adjusted to reveal anterior nasal spine (ANS) and second cervical vertebra (axis). Symmetry index passed through the center of ANS and axis to achieve symmetry. Next, axial sections were assessed. The largest dimension of longitudinal axis of each condyle (connecting its inner and outer poles) was measured (Figure 1), and then its angulation relative to sagittal plane was calculated (Figure 2).
Panoramic images were obtained with RayScan dental X-ray system (South Korea), as instructed by the manufacturer, with 69-90 kVp, 7 mA, 14-16 second time, and Scanner v. 2.0.1 software. The largest antero-posterior dimension of the condylar head (from the most prominent point of condylar convexity in the posterior region of condylar head to the anterior part of pterygoid fossa) was calculated bilaterally using a measurement tool of the software (Figure 3). All the measured values were recorded in a checklist.

Statistical analysis

Linear regression was applied to analyze the correlation between the right and left condylar angulation on CBCT scans and the right and left condylar size on panoramic radiographs. All statistical analyses were carried out using SPSS version 19 (SPSS Inc., IL, USA), with 0.05 level of significance.

Results

A total of 35 patients (35 CBCT scans and 35 pano­ramic radiographs) were evaluated in this study, out of which 20 (57.1%) were females and 15 (42.9%) were males. The mean age of patients was 46.38 ± 9.92 years (range, 26-70 years).
Table 1 presents the size (mm) and angulation (degrees) of the right and left condyles on the panoramic radiographs and CBCT scans. The linear regression test revealed that each 1-degree increase in the angulation of the right and left condyles on CBCT scans increased the size of the right and left condyles on panoramic radiographs by 0.03 mm, but this increase was not statistically significant (p = 0.33). The linear regression test also showed that by considering the left condyle as a reference for comparison of the effect of angulation change, each 1-degree increase in the right condyle angulation on CBCT scans increased the size of the right condyle on panoramic radiographs by 0.11 mm, and this increase was statistically significant (p < 0.001).

Discussion

This study assessed the condylar position on CBCT images and its correlation with the condylar size on panoramic radiographs. The results showed that by each 1-degree increase in the angulation of the right and left condyles on CBCT scans, the size of the right and left condyles increased by 0.03 mm on panoramic radiographs, but this increase was not statistically significant. However, this increase may become significant in a larger sample size. By considering the left condyle as the reference for comparison of the effect of changing the angulation, the results showed that by each 1-degree increase in the angulation of the right condyle on CBCT scans, the size of the right condyle on panoramic radiographs increased by 0.11 mm, and this increase was statistically significant.
Yokuş [9] reported the condylar size in antero-posterior dimension to be 6.70 ± 2.58 mm in males and 5.78 ± 1.28 mm in females, which was different from the values obtained in the present study. They assessed 400 condyles in the sagittal plane on MRI images. In the present study, the mean condylar size on panoramic radiographs was 10.86 mm and 10.47 mm in the right and left sides, respectively. Difference between the results of the two studies regarding the antero-posterior dimension of the condyles can be due to non-parallel position of the tube with the antero-posterior axis of the condyle in panoramic radiography; whereas MRI shows a corrected oblique sagittal view and the actual size of antero-posterior dimension of the condyles. Therefore, smaller values are expected to be reported by MRI. Also, panoramic images have magnification. They reported the condylar size in medio-lateral dimension on the axial view to be 18.77 ± 2.84 mm in males and 17.01 ± 2.29 mm in females, which was consistent with the present findings. In the present study, the mean condylar size in medio-lateral dimension on the axial view of CBCT scans was calculated to be 18.70 mm [9].
An inherent limitation of panoramic imaging is the superimposition of lateral and medial condyle poles, which hinders the precise representation of anterior-posterior dimension. Positional variation of these poles influenced by the horizontal condylar angle underscores the need for caution when interpreting measurements derived solely from panoramic views [10]. Variability in condylar angulations, especially horizontal condylar angulation, underlines the limitations of panoramic radiographs in accurately representing the condyle. As such, relying solely on panoramic imaging for comprehensive evaluation of the condyles, considering diverse angulations and magnifications, might be misleading [11].
Guercio Monaco et al. [12] measured the mean size of condyles in medio-lateral and antero-posterior dimensions to be 18.87 and 8.01 mm, respectively, by evaluating 100 condyles on CBCT scans. Their results regarding the size of medio-lateral dimension of the condyle were in agreement with the present findings. However, different values were reported regarding the antero-posterior dimension of the condyles, which could be due to magnification in panoramic radiography, different measurement techniques, or different sample sizes. Luo et al. [13] studied 186 sound condyles of young asymptomatic adults using MRI. They reported the size of condylar head to be 8.49 ± 1.04 mm in antero-posterior and 18.89 ± 1.58 mm in medio-lateral dimensions. Their results in medio-lateral dimension were in line with the present findings. However, their results in antero-posterior dimension were different from the measured values in the present study, probably due to different types of imaging modalities and different techniques of measurements. De Souza Nascimento et al. [14] studied the condyles of skeletal class II and III patients using CBCT. They measured the angle formed between the largest longitudinal axis of each condyle (connecting the inner and outer poles) and the coronal plane on the axial view, and found that the condylar angle relative to the coronal plane was 27.12 degrees in skeletal class II and 19.25 degrees in skeletal class III individuals. Their results are different from the current findings, which may be due to different inclusion criteria. The angle between the condylar axis and coronal plane in the present study was 21.72 degrees.
Lee et al. [15] assessed the correlation of horizontal condylar angle with TMJ osteoarthritis by evaluation of 86 sound condyles on CBCT images. They measured the angle formed between the largest condylar axis and coronal plane, which was 22.5 ± 7.7 degrees; this value was close to the value obtained in the present study (the mean angle of condyles relative to the sagittal plane was 21.72 degrees in the present study). Benson and Frederiksen [16] calculated the horizontal condylar angle on submentovertex images. They evaluated 16 TMJs and drew one line from the longitudinal axis of condyles and another line from the most posterior part of external auditory canal in the right and left sides. The formed angle was measured by a protractor and was considered as the horizontal condylar angle, which was 22 degrees for the right TMJ and 26 degrees for the left TMJ. These values were different from those of the present study due to different imaging modalities and methods of measurements. In the present study, the right and left condylar angles relative to the coronal plane were 20.13 and 23.31 degrees, respectively.
In total, the measurements made on the axial sections of different imaging modalities, such as MRI, CBCT, and even conventional extra-oral radiography were consistent with the present measurements of the condyles in medio-lateral dimension, and also the condylar angle relative to the sagittal plane on the axial section, which indicates that the axial section of different imaging modalities is more reliable for such measurements. How­ever, dimensions measured on panoramic radiographs are less reliable, and further investigations are warranted on this topic. Although no significant difference was found between CBCT and panoramic measurements within the population size of the current study, this crucial issue might require further examination using phantom models with their capability to manipulate the condyle’s neck and adjust its angle. A broader statistical population size can also contribute to further clarity on this subject.

Conclusions

The present results showed no significant correlation between the right and left condylar angles on CBCT scans with the right and left condylar size on panoramic radiographs. However, the difference in the right and left condylar angles on CBCT scans showed a significant correlation with the difference in condylar size on panoramic radiographs, such that by each 1-degree increase in the right condylar angle on CBCT scans, the right condylar size increased by 0.11 mm on panoramic radiographs.

Disclosures

1. Institutional review board statement: The study was approved by the Ethics Committee of Tabriz University of Medical Sciences, with approval number: IR.TBZMED.REC.1400.906.
2. Assistance with the article: None.
3. Financial support and sponsorship: None.
4. Conflicts of interest: The authors declare no potential conflicts of interest concerning the research, authorship, and/or publication of this article.

References