This study was done to assess TMJ changes in RA patients and their relative to disease chronicity and comparing the diagnostic effectiveness of CBCT and MRI in detecting radiographic changes of TMJs. There is no international radiographic classification or scoring measurements to evaluate TMJ changes in RA patients.11 Therefore, we aimed to find TMJ changes as dimensional condylar changes and radiographic osteoarthritic features.
In our study, the frequency of TMJ involvement in RA patients was 85%, while it was reported to vary from 2–86% in other studies.12–14 Such differences might be due to the different types of examination, patient selection criteria, the use of diagnostic techniques and the inclusion criteria. Based on the results of some other studies, same damaging pathway as found in other joints also seen in TMJ involvement which believed to be is straightly related to the severity and extent of RA.15 These findings are not confirmed by our study and some other studies.16
In our RA patients, 25% of patients had facial pain followed by jaw pain (20%), then clicking during mouth opening (2.5%), and muscle pain and joint pain during a right lateral excursion of the mandible (2.5%). TMJ pain was found in 65%, muscle pain in 42%, and joint sound in 51% of RA patients in a study done in Iran.16 Such differences might be related to examination methods of TMJs, variation in the number of included cases, types and frequency of drug intake in RA patients and inclusion of cases with TMD.
In the current study, the mean of unassisted opening and maximum unassisted opening of mouth were close to each other in RA (39.03 mm) and control (44.5 mm) groups. In contrast, the mean of maximum assisted mouth opening in RA patients was 39.65 mm and 44.8 mm in the control group, which was higher than the results found by Ardic et al., 2006,17 who reported unassisted opening to be 37.5 mm in RA and 39.1 mm in control groups, however, they reported higher range of assisted opening (44.3 mm in RA and 45.2 mm in control groups).
Additionally, we found that the mean of right lateral jaw excursion was 5.63 mm in RA and 9.5 mm in control groups, while the mean of left lateral jaw excursion was 5.63 mm and 7.2 mm in RA and control groups. These findings were lower than the results of a study that reported right excursion of 6.7 mm and 8.7 mm in RA and control groups, respectively and left excursion of 6.9 mm and 7.9 mm in RA control groups, respectively.17 Most studies show a decreased range of motion in RA patients, which might be caused by reduced joint space, sclerosis, or changed condylar positioned as an adaptive procedure.
In our study, we investigated four laboratory tests of RA (ESR, RF, CRP and Anti-CCP) to find any correlation between them and radiographic changes of TMJs. There was a positive correlation between ESR, RF, Anti-CCP with radiographic changes detected on TMJs. Regarding our ESR and FR outcomes, they were agreed with a study done in Iran.16 However, our results for the relation between RF and Anti-CCP with radiographic changes are controversial to a study done in Egypt. 11
In our RA patients, the most common osseous change was condylar head erosion (67.5%) which was higher than the results of other studies18 19 who reported 13.3% and 50%, respectively, and close to the result found by Gheita et al., 2012 20 (62.5%) but lower than those found by other studies21,22 who reported 72% and 85%, respectively. We detected flattening in both RA and control groups (65% and 50%, respectively) which was close to the results of a study conducted in Egypt 23 who found 89.3% and 50%, respectively and higher than the results of Voog et al., 2004 who found 30% flattening in RA patients. 19
Moreover, we found subchondral cyst only in the RA group (17.5%), which was higher than the outcomes of Deoghare and Degwekar, 201022 (10%) but was lower than some other researches18–20, 23 who reported 32.1%, 23.3%, 30%, and 20.83%, respectively. Furthermore, we found sclerosis in the RA patients (15%), which was much lower than the results reported by other studies19, 20, 23 who reported 64.3%, 75%, and 41.67%, respectively.
In our RA patients, the frequency of osseous change of condyle (erosion) was 80% which was in agreement with results found by other studies24, 25 who reported 80% and 83.3%, respectively but higher than Abdel Aziz and Esha, 201726 (52.5%), and lower than the result of a study conducted in Japan27 who found erosion in 96% of RA cases. On the other hand, the frequency of articular eminence erosion was 25% which was higher than the results reported by other studies25, 27 who found 9.5% and 8.2%, respectively, but lower than the reported result26 (50%). Whereas, the condylar head flattening was seen in 25%, higher than the results found by Abdel Aziz and Esha, 2017, Hirahara et al., 2017 (15% and 16.6%, respectively). 25, 26
In our patients, synovial proliferation was found in 20%, which is different from the results of other studies25, 27, who reported 100% and 85.7%, respectively. The frequency of effusion was 10% which was much lower than the results reported by other studies24, 25, 27 who reported 67.5%, 30.9%, and 33%, respectively. Consequently, the mean condylar length was 6.88 mm in RA patients and 7.61 mm in control cases, which was lower than the results of Youssef et al., 2020 who found 8.66 mm in RA and 8.27 mm in control groups11. Our results for control cases were close to the results of a study done in Malaysia10 (7.50 mm in Malays and 7.20 mm in Chinese). The mean of condylar width was 16.77 mm in RA patients and 16.53 mm in control cases which were slightly lower than the results reported by other researchers10, 11 who found 17.89 mm in RA/17.99 mm in controls and 17.18 mm in Malays and 17.80 mm in Chinese, respectively but was higher than the results reported by Manja and Rajaduray, 201928 who found 11.67 mm in patients with clicking and 11.18 mm in patients without clicking.
Consequently, in this study, the mean of condylar height was 18.02 mm in RA patients and 21.14 mm in control cases which were close to results found by Manja and Rajaduray, 201928, who found 18.9 mm in patients with clicking and 22.81 mm in patients without clicking) and by Al-koshab et al., 2015 (17.0 mm in Malays and 18.37 mm in Chinese). 10 Our results were much higher than Youssef et al., 2020 (4.3 mm in RA and 4.87 mm in control cases). 11 These drastic differences might be related to the height measurement method that is almost done from the most superior point of the condylar head down to the line of measuring the ML dimension of the condyle. The only decreased measurement was in the condylar height of RA patients concerning control cases that indicate bone changes in the upper condylar surface with fewer or no damage in the other sides.
Comparison of CBCT and MRI
Many researchers stated the high capacity and superiority of CBCT in evaluating osseous changes of the TMJ than other imaging modalities. 29 Due to the great consistency of CBCT established by previous researches, we reflected CBCT a gold standard in estimating osseous damages compared to MRI.
However, the investigative capability of MRI to find osseous alterations of the TMJ using cadaver samples had been evaluated. This study demonstrated that the MRI had 75% sensitivity and 84% specificity in detecting osseous abnormalities. In this regard, evaluation of 106 TMJs was done by CBCT, and MRI and low sensitivity (30–82%) with high specificity (84–90%) of MRI for detecting osseous abnormalities were seen30 as well as a study on 20 TMJs was done and sensitivity of 25–90.9% with a specificity of 70.8–97.2% were found26. Generally, the low sensitivity of MRI in detecting osseous abnormalities might be due to the restricted resolution of MRI, and the slice thickness of MRI, as mainly ≥ 3 mm is used, which might be too profuse to identify indirect osseous damages. 31 Additionally, fibrous tissues within TMJ and the connection of the lateral pterygoid muscle nearby the articular surface of the condyle, which can be explained as either an osseous anomaly or as a disc. They may result in false-positive or -negative findings. 32 Finally, when identifying osseous deformities in the articular fossa and eminence, complications sometimes rise by the magnetic susceptibility artefacts. 33, 34