Today, a significant increase in TMD prevalence is observed, with a rate of 10–70% in the general population and 16–68% in children and adolescents. The increasing number of TMD cases may be related to increased psychological pressure on today’s society. Besides these disorders, there may be different causes for several different specific conditions. The similarity of symptoms for different disorders causes difficulties in clinical diagnosis [9].
In addition to the primary clinical examination, various methods, and techniques for diagnosing TMD. MRI is accepted as the gold standard in the evaluation of articular disc as well as soft tissues. On the other hand, CT is used to diagnose bone lesions, such as bone erosion, fractures, postoperative deformities, and deformities of the temporal bone. Bone scintigraphy is helpful for the evaluation of osteoarthritis and joint inflammation. In recent years, the US has been defined as an essential method for imaging the TMJ. [9, 10].
First, it is necessary to determine which imaging methods are suitable for TMD diagnosis. Choosing the appropriate imaging modality depends on what kind of information the referring clinician wants. Although each imaging technique has its strengths and weaknesses, information about the location of the disc may be required in most cases to diagnose TMD [11, 12].
Detailed clinical, physical and additional psychological examinations are considered the gold standard for diagnosing TMD. Clark et al. According to TMD, the only need for imaging is to generate critical information that can influence treatment decisions [13]. If the method does not generate such information, the cost–benefit ratio of the procedure is meager. However, since the clinical diagnosis of TMD is based on the patient’s symptoms together with an objective assessment, researchers have reported that TMJ diseases cannot be reliably evaluated by clinical examination alone [14, 15].
Elias et al. reported in their study that the normal TMJ range was 1.4–1.6 mm on the US scans in adults [16]. In their study, Kirkhus et al. found the mean joint space distance in the US to be 1.3 ± 0.67 [0.4–3.4] with the mouth closed. He calculated the median value of the joint space distance as 0.9 on average [17]. Our study calculated the mean joint space distance 1.39 ± 0.51 [0.6–3.2] on the right and 1.38 ± 0.50 [0.7–3.2] on the left. We calculated the median value of the joint space distance as 1.3 on the right and 1.35 on the left. We saw similar results in both studies.
Melchiorre et al., in their study of 68 children and adolescents with an average age of 11, calculated that the average joint distance was less than 1.4 mm [18].
In their study with 30 participants, Kumar et al. found the TMJ interval distance of 0.04 mm with mouth closed and 0.11 mm with mouth open in the US scans in adults with temporomandibular dysfunction [19]. Our study found the joint space distance in the US as closed mouth 1.39 mm on the right and 1.38 mm on the left. We found it 1.27 mm on the right and 1.28 mm on the left in the open mouth. We obtained quite different results from these studies in the literature.
In their study of 23 patients, Uysal et al. diagnosed 34.4% of Disc Displacement with Reduction, 37.5% of Disc Displacement without Reduction, and 28.12% of healthy discs [20]. In their study of 74 patients, Talmaceanu et al. were diagnosed as 43.24% healthy disc, 30.41% Disc Displacement with Reduction, and 20.27% Disc Displacement without Reduction. [21]. Our study diagnosed 52% of healthy disc, 5% of Disc Displacement without Reduction, and 43% of Disc Displacement with Reduction for right TMJ. We diagnosed 51% healthy disc, 5% Disc Displacement without Reduction for left TMJ, and 44% Disc Displacement with Reduction. When the clinical diagnoses were examined, we saw that the rates of people diagnosed with Disc Displacement with Reduction and healthy disc among these studies in the literature were relatively high, but we had meager rates for the diagnosis of Disc Displacement without Reduction.
In general, two possible reasons for increased masseter muscle thickness are considered. First, an increase in muscle fiber filament and fiber diameter causes thickening when a muscle contracts. Another possible cause is increased edema in the muscle [22].
According to Franks, the temporal muscle usually takes an active role in fast, short movements but in long-term contractions, such as masseter muscle bruxism. This event is one of the reasons for the high incidence of masseter muscle tenderness [23].
Although CT and MRI are used to view the normal anatomy and pathology of the masseter muscle, thanks to significant advances in diagnostic imaging technology, real-time US is an accurate method for measuring muscle thickness as it is considered an easy and repetitive, non-invasive, and inexpensive procedure. Based on this information, US was used for masseter muscle thickness measurements in our study [24].
Telkar et al. found the mean US thickness of the resting masseter muscle to be 8.71 ± 0.44 [7.90–9.40] mm in their study of 47 patients [25]. In our study, we calculated the resting US thickness of the right masseter muscle as 8.71 ± 1.91 [5.2–17.30] mm, and the left masseter muscle as i8.62 ± 1.69 [4.7–13.30] mm. We found that the finding we obtained in our study was quite similar to the literature.
Nabeih and Speculand first performed US imaging of the TMJ and disc in 1991 with a 3.5 MHz transducer. In 1992, Stefanoff et al. reported successful results by evaluating the TMJ disc with a 5 MHz transducer in asymptomatic participants [26, 27]. After these preliminary studies, several publications have shown the sensitivity, specificity, and accuracy in imaging the TMJ condyle–disc position. Most studies have emphasized the diagnostic value of US compared to MRI findings [28, 29].
Although the specificity, sensitivity, and accuracy in the diagnosis of disc displacement are lower than MRI and CT, it has been suggested that it is a valuable method for examinations performed in large groups. In the presence of intracapsular irregularity, it was reported that MRI and US were in good agreement in determining the disc position [20].
The most significant advantage of the US is that it helps the diagnosis of TMJ intracapsular irregularities at a much lower cost than MRI. In this sense, studies on the US’s potential use and diagnostic capacity are increasing [14].
