Angular Evaluation of the TMJ Using Axial MRI: Vector-Based Analysis of Condylar and Lateral Pterygoid Angles in Anterior Disc Displacement

Angular Evaluation of the TMJ Using Axial MRI: Vector-Based Analysis of Condylar and Lateral Pterygoid Angles in Anterior Disc Displacement | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Angular Evaluation of the TMJ Using Axial MRI: Vector-Based Analysis of Condylar and Lateral Pterygoid Angles in Anterior Disc Displacement Muhammed Enes Naralan, Binali Çakır This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6756792/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 14 Nov, 2025 Read the published version in Scientific Reports → Version 1 posted 11 You are reading this latest preprint version Abstract This study aimed to investigate angular changes in the temporomandibular joint (TMJ) associated with anterior disc displacement (ADD) through axial magnetic resonance imaging (MRI). Specifically, the lateral pterygoid muscle (LPM) attachment angle and the condylar position angle were evaluated using a coordinate-based vector analysis method. A total of 151 patients and 302 TMJs were retrospectively evaluated. Joints were categorized into three groups: healthy, ADD with reduction (ADDwR), and ADD without reduction (ADDwoR). On axial MRI slices, angular measurements were obtained using a pixel-based coordinate system and calculated using the dot product method. Intra-observer reliability was assessed using intraclass correlation coefficients (ICCs). Measurement reliability was high (ICC = 0.965 for LPM angle, ICC = 0.969 for condylar angle). No significant differences were found in LPM angle between groups (p = 0.51). In contrast, condylar position angle was significantly lower in both ADD groups compared to healthy joints (p = 0.01). No statistically significant difference was observed between the ADDwR and ADDwoR groups. A significant decrease in condylar position angle was observed in joints affected by ADD, possibly indicating adaptive joint remodelling over time. However, no angular change was observed in the attachment angle of the lateral pterygoid muscle. The vector-based measurement method demonstrated high intra-observer reliability and may offer a reproducible approach for angular assessment of TMJ structures. Health sciences/Health care/Medical imaging/Magnetic resonance imaging Health sciences/Health care/Dentistry/Dental radiology Temporomandibular joint anterior disc displacement lateral pterygoid muscle condylar position angular analysis MRI dot product Figures Figure 1 Introduction The temporomandibular joint (TMJ) is a diarthrodial joint formed by the mandibular condyle and the mandibular fossa of the temporal bone, playing a key role in essential functions such as chewing, speaking, and swallowing. The stability and mobility of this joint are closely related to surrounding tissues, particularly the function of the lateral pterygoid muscle (LPM). 1 The LPM is primarily responsible for mandibular protrusion and lateral deviation, as well as assisting in mouth opening. 2 This muscle has two heads: the superior head attaches to the articular disc and capsule to ensure disc stability, while the inferior head functions in mandibular opening and protrusion. 3 Among temporomandibular joint disorders (TMD), anterior disc displacement (ADD) is one of the most frequently encountered pathologies. 4 , 5 ADD is characterized by anterior displacement of the articular disc relative to the condyle, which may result in joint pain, limited mouth opening, and chewing difficulty. 1 , 3 ADD is classified into two main types: anterior disc displacement with reduction (ADDwR) and anterior disc displacement without reduction (ADDwoR). In particular, in long-standing and untreated cases of ADD, notable morphological changes occur in the condyle and articular disc. 6 , 7 Prolonged condylar displacement may lead to the condyle repositioning within a new fossa, and during this process, changes such as fibrosis within the joint, perforation in retrodiscal tissues, and cartilage degeneration can be observed. 6 , 8 The LPM exhibits significant morphological and functional alterations depending on the presence and duration of ADD. In short-term conditions, hypertrophy may occur as a compensatory mechanism to maintain joint stability; whereas in chronic ADD cases, atrophy, fat infiltration, and fibrosis become prominent. 9 – 11 These pathological changes in the LPM are associated with reduced functional capacity and increased intramuscular heterogeneity. 7 , 12 Several studies have reported notable atrophy and increased T1 signal intensity in the LPM, particularly in ADDwR cases. 9 , 10 Biomechanical factors play a crucial role in the functional stability of the TMJ. The relationship between muscle force and joint angle is a critical element in the regulation of TMJ movement. 13 – 15 As the angle between the direction of muscle pull and the position of the condyle increases, the risk of anterior disc displacement rises. 5 , 15 , 16 In particular, hypertonicity of the superior head of the LPM has been identified as a major contributing factor in the development of ADD. 1 , 4 While previous studies have indicated that alterations in joint angles may contribute to disc displacement, few have quantitatively evaluated the angular relationship between the lateral pterygoid muscle vector and condylar position in vivo. Among imaging modalities, magnetic resonance imaging (MRI) is considered the most reliable method for evaluating the soft tissue structures of the TMJ. 9 , 17 MRI allows for detailed assessment of disc position, condylar morphology, and structural changes in the LPM, such as fat infiltration, atrophy, and fibrosis. 10 , 11 Among MRI planes, axial slices provide the most reliable visualization of the lateral pterygoid muscle’s orientation and its attachment to the condyle, allowing for accurate vector-based angular assessment. Mathematical methods such as the dot product can be used to calculate angular relationships between the muscle and the condyle. 18 , 19 By utilizing pixel-based positional data, the angle between two vectors can be reliably calculated. This makes it possible to quantify angular changes between the pulling direction of the LPM and the position of the condyle, thus revealing the role of these changes in the development of ADD. 14 , 20 This method can numerically demonstrate both alterations in the LPM’s direction of pull and changes in condylar position. Hence, it enables direct measurement of the impact of muscle and joint biomechanics on the pathogenesis of ADD. In this retrospective study, the LPM attachment angle and condylar position angle values in healthy individuals were established, and changes in these angles in patients with ADD were evaluated. We hypothesized that patients with ADD would show a decreased condylar position angle and possible changes in the LPM attachment angle, with variations depending on ADD subtype. The aim of this study is to evaluate, through an MRI-based vectorial analysis, the changes in the LPM attachment angle and condylar position angle in individuals with ADD, and to explore the potential relationship between these angles and the development of ADD. Material method This study was approved by the Non-Interventional Ethics Committee of Recep Tayyip Erdoğan University (2025/86) and was conducted in accordance with the principles of the Declaration of Helsinki. As the study had a retrospective design, the requirement for informed consent was waived by the ethics committee. The research was carried out in the Departments of Oral and Maxillofacial Radiology at the Faculties of Dentistry of Recep Tayyip Erdoğan University and Atatürk University. Patients who underwent MRI examinations for temporomandibular joint disorders between September 1, 2022, and January 1, 2025, were included. Clinical records were reviewed to confirm that imaging was requested primarily for joint-related complaints rather than incidental findings. Inclusion criteria for MRI images consisted of images oriented such that axial planes were parallel to the ground, sagittal planes were perpendicular to the ground, and coronal planes were perpendicular to the sagittal plane. Radiologically healthy individuals and patients diagnosed solely with ADD were included. Radiologically healthy individuals (no disc displacement or osseous pathology) and patients diagnosed exclusively with ADD, based on MRI criteria, were included. Patients with systemic diseases, abnormal bony changes, arthritis, or other joint pathologies, as well as those with artifacts or positioning errors on MRI, were excluded. MRI images used in the study were obtained using 1.5 Tesla Siemens Magnetom Aera, 1.5 Tesla Siemens Magnetom Avanto, and 3 Tesla Siemens Magnetom Skyra systems (Siemens Medical Systems, Erlangen, Germany). The imaging protocol included T1-weighted and T2-weighted sequences. T1-weighted sequences were acquired with a repetition time (TR) ranging from 7 to 8.6 ms and an echo time (TE) between 2.95 and 4 ms. T2-weighted sequences had TR values up to 3500 ms and TE values up to 120 ms (in specific sequences not used for angular measurement). Slice thickness varied between 3 and 5 mm, and all images were obtained with a 512×512 matrix and field of view (FOV) between 250–260 mm. No contrast agent was administered. ADD assessment was performed using parasagittal T1 and T2 sequences. In the closed-mouth position, if the articular disc exceeded + 10° anterior to the 12 o'clock position of the condyle, it was considered indicative of ADD.⁶ In the open-mouth position, re-establishment of the disc over the condyle was classified as ADDwR, while failure to reposition was classified as ADDwoR. Coordinate determination and angular measurements were performed on axial MRI slices using a pixel-based coordinate system. Analyses were conducted using the MicroDicom DICOM Viewer (MicroDicom Ltd, Sofia, Bulgaria). The evaluation was performed on the axial slice where the LPM was most prominently visible. The origin point of the muscle (x1, y1) was marked as the starting point, and the insertion point (x2, y2) was defined as the midpoint where the muscle attaches to the condyle. The medial and lateral poles of the condyle were marked at coordinates (x3, y3) and (x4, y4), respectively, in the slice where the condyle appeared widest. This pixel-based coordinate plane enabled precise measurements at the smallest units of the image, and all measurements were performed using this system. This coordinate-based measurement process is illustrated in Fig. 1 , which demonstrates the anatomical landmarks and vector orientations used for angular calculations. To assess the position of the condyle and establish a standard reference plane, a perpendicular projection from the lateral pole of the condyle (x4, y4) to the coronal plane was created in the axial slice where the condyle was widest. The projection point was defined by combining the x-coordinate of the lateral pole with the y-coordinate of the medial pole, creating a reference point at (x4, y3). In this study, the reference plane was defined by the vector between this projection point (x4, y3) and the medial pole of the condyle (x3, y3). Orientation and angular measurements were standardized based on this reference vector. This method ensured consistency in measuring the condyle’s position relative to a fixed reference plane. Two primary angular measurements were conducted: the LPM angle (angle formed between the muscle and the condyle) and the condylar position angle (angle between the condyle and the coronal plane).¹⁹ The dot product method was used to calculate the angles between two vectors, using the following formula: $$\:{\theta\:}=\text{arccos}\left(\frac{\left({x}_{2}-{x}_{1}\right)\cdot\:\left({x}_{4}-{x}_{3}\right)+\left({y}_{2}-{y}_{1}\right)\cdot\:\left({y}_{4}-{y}_{3}\right)}{\sqrt{{\left({x}_{2}-{x}_{1}\right)}^{2}+{\left({y}_{2}-{y}_{1}\right)}^{2}}\cdot\:\sqrt{{\left({x}_{4}-{x}_{3}\right)}^{2}+{\left({y}_{4}-{y}_{3}\right)}^{2}}}\right)$$ Angular measurements were calculated using the dot product, which provides the cosine of the angle between two vectors and ensures consistent directional assessment within the coordinate system. All coordinates were recorded at the pixel level, ensuring high-resolution measurement accuracy. The orientations of the vectors between the muscle and condyle were determined relative to this reference plane, and all measurements were conducted by a single dentomaxillofacial specialist (M.E.N). To assess measurement reliability, repeated measurements were performed on 25% of randomly selected cases. To evaluate intra-observer reliability, intraclass correlation coefficient (ICC) values with 95% confidence intervals were calculated using a two-way random-effects model (absolute agreement, single measurement). The obtained coordinate data were processed using formulas in Office 360 Excel (Microsoft, Seattle, USA) and used in statistical analyses. Statistical analysis was performed using SPSS 29.0 (IBM Corp., Armonk, NY, USA). The distribution characteristics of continuous variables were evaluated using the Kolmogorov-Smirnov and Shapiro-Wilk normality tests. Since the data were not normally distributed, non-parametric test methods were employed. Differences between right and left sides in healthy individuals were evaluated with the Wilcoxon test, and comparisons between groups were made using the Kruskal-Wallis H test. For variables with significant differences according to the Kruskal-Wallis test, the Post-hoc Dunn test was applied to identify which groups were responsible for the differences. The Mann-Whitney U test was used for comparisons based on sex. A p-value of < 0.05 was considered statistically significant for all analyses. Results A total of 151 patients and 302 TMJs were included in this study. The study sample included 115 females (76.2%) and 36 males (23.8%), with a mean age of 38.9 ± 12.4 years. When evaluating the joints included in the study, Of the 302 joints evaluated, 144 (47.7%) were classified as healthy, 110 (36.4%) as ADDwR, and 48 (15.9%) as ADDwoR. Intra-observer reliability was assessed using the ICC based on a two-way random-effects model, single-measurement, absolute agreement. Intra-observer reliability was excellent, with ICC values of 0.965 (95% CI: 0.943–0.981) for the LPM angle and 0.969 (95% CI: 0.948–0.984) for the condylar angle. ²¹ For the LPM attachment angle, the median value for the left joint was 69.43° (min: 41.64°, max: 83.18°), with a mean of 68.30° ± 8.79°. For the right joint, the median value was 70.20° (min: 46.27°, max: 177.52°), with a mean of 75.10° ± 26.31°. Regarding the condylar angle, the median value for the left joint was 159.12° (min: 137.07°, max: 179.99°), with a mean of 159.18° ± 7.95°. For the right joint, the median value was 157.69° (min: 145.01°, max: 179.84°), with a mean of 159.49° ± 7.93°. To evaluate whether there were statistical differences in measurements of healthy joints between genders, the Mann-Whitney U test was used. The p-value for the LPM attachment angle was found to be 0.163, indicating no statistically significant difference between male and female patients. Similarly, the p-value for the condylar position angle was calculated as 0.104, showing no significant difference between genders. These findings indicate that sex does not significantly affect the LPM attachment angle or condylar position angle in healthy individuals. When the LPM attachment angle and condylar position angle in healthy individuals were evaluated using the Wilcoxon test, no significant difference was observed between the right and left joints. These findings suggest that angular symmetry is maintained between the right and left TMJs in healthy individuals, supporting the anatomical consistency of the measurement method. According to the results of the Kruskal-Wallis test, there was no statistically significant difference in LPM attachment angle among the groups (p = 0.51). This result confirms that LPM attachment angle does not significantly differ across the three groups, including healthy, ADDwR, and ADDwoR. On the other hand, analysis of the condylar position angle revealed a significant difference among the groups (p = 0.01), suggesting a potential relationship between condylar position and the presence of ADD. Notably, the condylar angle in the ADDwoR group was lower compared to healthy individuals. (Table 1 ) Table 1 LPM Attachment Angle and Condylar Position Angle Across Groups with Kruskal-Wallis Test Results n Median LPM Attachment Angle(Min.–Max.) Median Condylar Position Angle (Min.–Max.) LPM Attachment Angle Group p -Value Condylar Angle Group p -Value Healthy 144 69.42 (41.64–177.52) 158.72 (137.07–179.99) 0.51 0.01* ADDwR 110 68.30 (31.77–178.03) 157.27 (140.53–177.45) ADDwoR 48 70.68 (50.08–143.14) 155.59 (133.10–177.89) * Indicates statistical significance based on Kruskal-Wallis test results ADDwR: Anterior disc displacement with reduction ADDwoR: Anterior disc displacement without reduction LPKA: Lateral pterygoid muscle attachment angle According to the results of the post-hoc Dunn test, a statistically significant difference in condylar position angle was found between healthy individuals and both ADDwR and ADDwoR patients. The p-value for the difference between the healthy group and the ADDwR group was calculated as 0.01, and the p-value for the difference between the healthy group and the ADDwoR group was also 0.01. On the other hand, no significant difference was observed between the ADDwR and ADDwoR groups (p = 0.46). Although ADD was associated with a significantly reduced condylar angle compared to healthy joints, no significant difference was observed between ADDwR and ADDwoR, suggesting that disc reduction status does not substantially influence this angular change. (Table 2 ) Table 2 Significance Levels of Condylar Position Angle Within Groups According to Post-hoc Dunn Test Comparison n p Healthy vs. ADDwR 144 0.01* Healthy vs. ADDwoR 110 0.01* ADDwR vs. ADDwoR 48 0.46 * Indicates statistical significance based on post-hoc Dunn test results ADDwR: Anterior disc displacement with reduction ADDwoR: Anterior disc displacement without reduction To further detail the differences between groups, the Mann-Whitney U test was applied. This test was conducted to determine whether there were statistically significant differences in LPM attachment angle and condylar position angle among healthy individuals, ADDwR patients, and ADDwoR patients. According to the results, no statistically significant differences were found in any of the comparisons regarding the LPM attachment angle (p > 0.05). Although no statistically significant difference was found, the median LPM angle values were slightly higher in healthy individuals compared to the ADDwR and ADDwoR groups. (Table 3 ) Table 3 Mann-Whitney U Test Results: Intergroup Comparisons of LPM Attachment Angle and Condylar Position Angle Comparison Median Difference U Value p -Value Direction of Difference (Higher Value) Lateral Pterygoid Muscle Attachment Angle Healthy vs. ADDwR 1,36 8765 0,14 Healthy Healthy vs. ADDwoR 0,01 3416 0,90 Healthy ADDwR vs. ADDwoR -1,35 2300 0,19 ADDwoR Condylar Position Angle Healthy vs. ADDwR 1,70 8212 0,61 Healthy Healthy vs. ADDwoR 2,26 3897 0,18 Healthy ADDwR vs. ADDwoR 0,55 2909 0,31 ADDwR ADDwR: Anterior disc displacement with reduction ADDwoR: Anterior disc displacement without reduction Statistically significant differences in condylar position angle were observed between healthy individuals and both ADD groups (p < 0.05). However, no significant difference was found between the ADDwR and ADDwoR groups. Overall, the condylar angle tended to be greater in healthy individuals. These findings suggest that changes in condylar position angle may be associated with anterior disc displacement. However, whether the ADD is with or without reduction does not appear to be a determining factor for the condylar position. Regarding the LPM attachment angle, no statistically significant difference was observed among the groups. Nonetheless, when the direction of the difference was examined, it was noted that the mean LPM angle was higher in healthy individuals. Discussion Our findings confirm that anterior disc displacement is associated with changes in condylar positioning, while LPM angular orientation appears unaffected. While the condylar position angle showed a significant change, the LPM attachment angle did not exhibit a meaningful difference. This contrast suggests that structural remodelling in the joint may occur independently of measurable angular changes in muscle orientation. In this study, no statistically significant differences were found between genders in terms of LPM attachment angle or condylar position angle. This finding is consistent with existing literature suggesting that gender does not have a marked effect on TMJ biomechanics. 12 , 21 While Melke et al. 22 reported that LPM volume is greater in males than in females, our study did not detect a significant angular difference between genders. The lack of angular difference between gneders contrasts with reports of LPM volume differences. This discrepancy may be due to differences in measurement parameters or sample composition, particularly the female-dominated cohort. The dot product method used for measurements in this study is consistent with other coordinate system approaches recommended in the literature for calculating joint angles. 19 , 23 – 25 In particular, Van Hauwermeiren et al. 19 proposed a standardized coordinate system to more objectively represent the biomechanical data of joints. This system, which is aligned with joint surfaces, provides high ICC values and enhances measurement consistency in complex geometric structures such as the TMJ. The high ICC values (0.965–0.969) indicate excellent intra-observer reliability, supporting the consistency of the coordinate-based method used. MRI is the gold standard for TMJ evaluation due to its superior soft tissue contrast and absence of radiation exposure 9 , 17 , 26 Although sagittal slices are commonly used to assess disc position and anterior-posterior condylar movement 1 , 9 they are limited in evaluating the orientation of the LPM. Since the LPM primarily operates in the anteroposterior plane, axial slices provide clearer visualization of its attachment and directional vector 7 , 11 , 15 , 27 , 28 Therefore, in this study, angular measurements were performed on axial slices, which offer a broader field of view for assessing both LPM orientation and mediolateral condylar deviations. All MRI systems used in this study had field strengths ≥ 1.5T, which are widely accepted in the literature as sufficient for joint and muscle evaluation. 29 Since the imaging methods were limited to two-dimensional (2D) axial slices, the spatial detail that could be provided by three-dimensional (3D) evaluations could not be obtained. In the literature, 3D imaging has been reported to enable a more accurate and comprehensive assessment of TMJ biomechanics. 7 , 11 From a clinical perspective, this limitation may have prevented a complete depiction of the three-dimensional spatial relationship between the muscle and the condyle. Despite the absence of 3D imaging, the anteroposterior orientation of the LPM justifies the use of axial 2D slices for this angular analysis. The literature emphasizes that the primary function of the LPM is to advance the mandible and maintain anteroposterior stability of the articular disc, and that the anteroposterior movement of the muscle plays a more decisive role in TMJ biomechanics. 5 Clinically, the fact that the LPM's main pulling direction is anteroposterior made it more meaningful for this study to focus on anteroposterior angles. Future imaging studies should examine the three-dimensional movement patterns of the muscle in greater detail to better reflect them in clinical applications. In presented study, no statistically significant difference was observed between the right and left TMJ structures. This finding aligns with the expected right-left symmetry in craniofacial anatomy. It also underscores the importance of the measurement method used in this study, demonstrating that it is both unbiased and anatomically consistent. Symmetry analyses conducted in different anatomical regions in the literature also support this outcome. For example, in a study evaluating the volume of the masseter muscle, no significant difference was found between the right and left sides in either individuals with scoliosis or control subjects. 30 Similarly, Bakhshayesh et al. used 3D imaging and volume fusion techniques to assess pelvic structures and reported that the right and left hemipelvis were clinically symmetrical in healthy individuals. 31 At the muscular function level, Tan et al. 32 showed that muscle synergies became more symmetrical between sides in patients undergoing robotic rehabilitation after stroke, and that this improvement developed alongside motor recovery. Additionally, Ren et al. 33 , analyzed and found a high degree of similarity in movement patterns between the right and left extremities in healthy individuals, while noting that this symmetry was disrupted in neurodegenerative diseases. All these findings suggest that the absence of side-to-side differences in our study is not only a physiologically expected result, but also an indicator of the validity of the method used. In this study, a statistically significant change in condylar position angle was detected in patients with ADD (p < 0.05). In the study by Wadhawan et al. 8 , it was reported that in patients with ADD, the condyle was positioned more posteriorly and superiorly, and that this adaptive change led to angular alterations in joint biomechanics. Similarly, in the study by Manfredini et al. 5 it was emphasized that hyperactivity of the LPM contributed to changes in condylar position. The observed decrease in condylar position angle among ADD patients supports prior findings of joint remodelling and posterior-superior displacement of the condyle in chronic cases. 15 The lower condylar angle observed particularly in ADDwoR patients indicates that compensatory changes may have occurred in the joint, potentially affecting joint function. The literature reports that in prolonged condylar displacements, fibrotic structures may form in an effort to increase joint stability, resulting in the condyle being fixed in a new position. 6 The findings of this study demonstrate the adaptive changes occurring in the condyles of patients with ADD. The observed decrease in condylar position angle in both ADDwR and ADDwoR groups raises the question of whether this angular change is a contributing factor to disc displacement or a result of chronic adaptation. While some studies have suggested that altered condylar orientation may precede disc displacement and facilitate its development through biomechanical misalignment 15 , others have reported that prolonged disc displacement can cause remodelling and posterior-superior condylar shift as a secondary outcome 8 . Given the cross-sectional nature of our study, causality cannot be established. However, the angular difference observed in both ADD subtypes—even in the absence of reduction—suggests that remodelling may play a larger role in shaping joint biomechanics over time. It has also been noted that this adaptation mechanism may limit joint mobilization in non-surgical treatments.⁸ This finding represents an important factor that should be considered in maintaining joint stability and planning treatment. It is suggested that conservative treatment approaches applied during the early stages of ADD may be more effective before morphological changes occur in the joint. In contrast, in advanced ADDwoR patients, biomechanical alterations within the joint may limit the success of non-surgical treatment approaches. In the study by Shahab et al. 15 it was shown that a condylar horizontal angle greater than 30° was associated with ADD, and that the intercondylar angle was smaller in patients with ADD. In our study, while no statistically significant difference was found in the LPM attachment angle, the condylar position angle was found to be associated with ADD. This discrepancy suggests that the angular parameters assessed may influence joint biomechanics in different ways. The study by Shahab et al. 15 focused on macro-level changes in condylar and joint mechanics, whereas our study evaluated the local effects of the LPM attachment angle. The study by Ren et al. 33 demonstrated that maintaining a stable disc position does not lead to significant morphological changes in the disc. When the disc remains in a stable position, it may not induce morphological changes in the LPM either, as the muscle’s requirement for active contraction is reduced. In contrast, the study by Ngamsom et al. 11 reported that in ADDwoR patients, the disc remains fixed in an anterior position, allowing the condyle to acquire a stable position as well, resulting in minimal angular differences. In current study, no statistically significant difference was found in the LPM attachment angle across groups. This result may be explained by two complementary factors: 1 the possibility of muscle adaptation in long-term ADD, where angular orientation remains stable despite internal structural changes (such as atrophy or fibrosis); and 2 the limitations of 2D MRI, which may fail to capture the full spatial orientation of the muscle. This suggests that while the LPM undergoes morphological changes in ADD, these may not always translate into measurable angular deviations on standard axial imaging. The findings of our study are consistent with these explanations in the literature. No significant difference in condylar position angle was found between ADDwR and ADDwoR patients. This finding suggests that whether ADD is with or without reduction may result in similar biomechanical outcomes in the joint. Similarly, the literature indicates that in the advanced stages of ADD, the condyle and articular disc may transition into a new stable position, leading to structural changes in the joint becoming fixed over time. 7 The literature indicates that the LPM undergoes significant morphological and functional changes in patients with ADD. In the study by Wang et al. 9 , increased severity of ADD was associated with fat infiltration and greater muscle heterogeneity in the LPM. These changes were reported to be especially prominent in the ADDwoR group and were linked to long-term dysfunction. The study by Ngamsom et al. 11 also reported alterations in the superior head of the LPM, including hypertrophy, atrophy, and contracture. The role of LPM hyperactivity in the pathogenesis of ADD is further supported by the study of Manfredini et al. 5 The lack of angular differences in the LPM may stem from the limitations of 2D imaging, which cannot fully capture the complexity of muscle orientation. Moreover, long-term disc displacement could lead to muscular adaptation that preserves angular alignment despite internal changes. The role of the LPM in the development of ADD has been addressed in various studies in the literature. For instance, some studies suggest that hyperactivity of the LPM may trigger the development of ADD, while others indicate that it may contribute to joint stability. In the study by Wang et al. 9 , it was reported that in the advanced stages of ADD, fat infiltration and atrophy occur in the LPM, leading to reduced muscle function. In the study by Ngamsom et al. 11 , no direct correlation was found between LPM hyperactivity and pathological changes in the joint. This may be another factor that explains why no significant difference was observed in the LPM angle in our study. The relationship between the LPM and anterior disc displacement has been addressed in numerous studies in the literature. In the study by Wang et al. 9 , it was reported that the LPM undergoes functional changes in conjunction with disc displacement; however, these changes could not be definitively correlated with angular parameters. Similarly, in the study by Liu et al. 10 , significant structural changes in the LPM were observed in the presence of ADD, but no direct association with angular measurements could be established. This does not imply a complete rejection of the hypothesis. The hypothesis that the LPM angle plays an important role in the development of ADD should be reconsidered considering factors such as compensatory adaptation of the muscle, varying patterns of muscle activity across different stages of the disorder, and methodological limitations. Particularly in advanced stages of ADD, the biomechanical function of the LPM may change, which could be reflected in its angular position. Furthermore, the low sample size in the ADDwoR group may have limited the detection of statistical differences. This may have contributed to the lack of significant findings in LPM attachment angle comparisons. This study offers a reproducible angular measurement approach for TMJ evaluation, though further validation with functional and 3D data is required to establish clinical utility. By applying a pixel-based vectorial analysis, it provides a reproducible method for evaluating angular changes in TMJ structures. While the approach shows promise for future studies, additional validation and functional correlations are needed to support its broader clinical application. This study has several limitations. First, the angular measurements were derived from two-dimensional MRI slices, which may not fully represent the three-dimensional dynamics of the lateral pterygoid muscle. Second, no functional assessments such as electromyography were performed to evaluate the muscle’s activity directly. Third, all measurements were conducted by a single observer. Although intra-observer reliability was excellent, the lack of inter-observer validation limits the generalizability of the results. Future studies should incorporate dynamic imaging and multi-observer analysis to validate and expand upon the current findings. In future studies, the functional movements of the LPM should be examined in more detail, and the dynamic structure of the muscle should be evaluated with additional imaging methods. Considering morphological parameters such as fat infiltration, fibre composition, and volumetric changes will further contribute to shaping clinical approaches for a better understanding of the role of the muscle in the ADD process. Conclusion The results of this study suggest a potential relationship between condylar position and anterior disc displacement, whereas no significant difference was found in muscle angle. These findings highlight the complexity of TMJ biomechanics and the need for comprehensive evaluation methods. The vector-based approach used here offers a reproducible technique for angular analysis, but further studies incorporating functional and three-dimensional assessments are required to confirm its clinical applicability. Declarations Competing interests The authors declare no competing interests. Funding No funding. Author Contribution M.E.N. designed the study, performed the data collection and angular measurements, conducted the statistical analysis, and wrote the initial draft of the manuscript. B.Ç. supervised the study, contributed to data interpretation, provided critical revisions, and approved the final version of the manuscript. All authors reviewed and approved the final manuscript. Acknowledgement The authors would like to thank Dr. Yüksel Sümeyra Naralan for providing valuable support and guidance in the statistical analysis of the study. The authors used a generative large language model solely to assist with language refinement and proofreading. All scientific content, including data analysis, interpretation, and the final approval of the manuscript, was entirely conducted and validated by the authors. Data Availability The datasets generated and/or analysed during the current study are not publicly available due to patient privacy restrictions but are available from the corresponding author on reasonable request. References Omami, G. & Lurie, A. Magnetic resonance imaging evaluation of discal attachment of superior head of lateral pterygoid muscle in individuals with symptomatic temporomandibular joint. Oral Surg. Oral Med. Oral Pathol. Oral Radiol. 114 , 650–657. 10.1016/j.oooo.2012.07.482 (2012). Dergin, G. et al. Evaluating the correlation between the lateral pterygoid muscle attachment type and internal derangement of the temporomandibular joint with an emphasis on MR imaging findings. J. Craniomaxillofac. Surg. 40 , 459–463. 10.1016/j.jcms.2011.08.002 (2012). Butts, R., Dunning, J., Perreault, T., Mettille, J. & Escaloni, J. Pathoanatomical characteristics of temporomandibular dysfunction: Where do we stand? (Narrative review part 1). J. Bodyw. Mov. 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Temporomandibular joint adaptations following two-phase therapy: an MRI study. Orthod. Craniofac. Res. 11 , 235–250. 10.1111/j.1601-6343.2008.00436.x (2008). Wang, S. et al. Evaluation of lateral pterygoid muscle in patients with temporomandibular joint anterior disk displacement using T1-weighted Dixon sequence: a retrospective study. BMC Musculoskelet. Disord . 23 , 125. 10.1186/s12891-022-05079-1 (2022). Liu, M. Q. et al. Functional changes of the lateral pterygoid muscle in patients with temporomandibular disorders: a pilot magnetic resonance images texture study. Chin. Med. J. (Engl) . 133 , 530–536. 10.1097/CM9.0000000000000658 (2020). Ngamsom, S. et al. The intravoxel incoherent motion MRI of lateral pterygoid muscle: a quantitative analysis in patients with temporomandibular joint disorders. Dentomaxillofac Radiol. 46 , 20160424. 10.1259/dmfr.20160424 (2017). Wang, S. et al. Gender differences in lateral pterygoid muscle in patients with anterior disk displacement. Oral Dis. 29 , 3481–3492. 10.1111/odi.14391 (2023). Nickel, J. C. et al. Mechanics- and Behavior-Related Temporomandibular Joint Differences. J. Dent. Res. 103 , 1083–1090. 10.1177/00220345241265670 (2024). Kundu, T., Zakir Hossain, M., Pluta, M. & Grill, W. in Health Monit. Struct. Biol. Systems 2013 (2013). Shahab, S., Amoozad Khalili, Z., Emami Meybodi, E. & Banakar, M. Relation between Condyle Horizontal Angle and Intercondylar Angle with Disc Displacement in Patients with Temporomandibular Joint Disorders: An MRI Evaluation. Radiol Res Pract 3846525, (2023). 10.1155/2023/3846525 (2023). Kohinata, K. et al. Retrospective magnetic resonance imaging study of risk factors associated with sideways disk displacement of the temporomandibular joint. J. Oral Sci. 58 , 29–34. 10.2334/josnusd.58.29 (2016). D'Ippolito, S. M. et al. Evaluation of the lateral pterygoid muscle using magnetic resonance imaging. Dentomaxillofac Radiol. 39 , 494–500. 10.1259/dmfr/80928433 (2010). van den Bogert, A. J., Geijtenbeek, T., Even-Zohar, O., Steenbrink, F. & Hardin, E. C. A real-time system for biomechanical analysis of human movement and muscle function. Med. Biol. Eng. Comput. 51 , 1069–1077. 10.1007/s11517-013-1076-z (2013). Van Hauwermeiren, L. et al. Joint coordinate system for biomechanical analysis of the sacroiliac joint. J. Orthop. Res. 37 , 1101–1109. 10.1002/jor.24271 (2019). Jakubowski, K. L., Ludvig, D., Bujnowski, D., Lee, S. S. M. & Perreault, E. J. Simultaneous Quantification of Ankle, Muscle, and Tendon Impedance in Humans. IEEE Trans. Biomed. Eng. 69 , 3657–3666. 10.1109/TBME.2022.3175646 (2022). Guerrero, M. E., Beltran, J., de Laat, A. & Jacobs, R. Can pterygoid plate asymmetry be linked to temporomandibular joint disorders? Imaging Sci. Dent. 45 , 89–94. 10.5624/isd.2015.45.2.89 (2015). Melke, G. S. F., Costa, A. L. F., Lopes, S., Fuziy, A. & Ferreira-Santos, R. I. Three-dimensional lateral pterygoid muscle volume: MRI analyses with insertion patterns correlation. Ann. Anat. 208 , 9–18. 10.1016/j.aanat.2016.05.007 (2016). Wu, G. et al. ISB recommendation on definitions of joint coordinate systems of various joints for the reporting of human joint motion–Part II: shoulder, elbow, wrist and hand. J. Biomech. 38 , 981–992. 10.1016/j.jbiomech.2004.05.042 (2005). Wu, G. & Cavanagh, P. R. ISB recommendations for standardization in the reporting of kinematic data. J. Biomech. 28 , 1257–1261. 10.1016/0021-9290(95)00017-c (1995). Wu, G. et al. ISB recommendation on definitions of joint coordinate system of various joints for the reporting of human joint motion–part I: ankle, hip, and spine. International Society of Biomechanics. J. Biomech. 35 , 543–548. 10.1016/s0021-9290(01)00222-6 (2002). Imanimoghaddam, M., Madani, A. S. & Hashemi, E. M. The evaluation of lateral pterygoid muscle pathologic changes and insertion patterns in temporomandibular joints with or without disc displacement using magnetic resonance imaging. Int. J. Oral Maxillofac. Surg. 42 , 1116–1120. 10.1016/j.ijom.2013.01.022 (2013). Segami, N. et al. Does joint effusion on T2 magnetic resonance images reflect synovitis? Part 2. Comparison of concentration levels of proinflammatory cytokines and total protein in synovial fluid of the temporomandibular joint with internal derangements and osteoarthrosis. Oral Surg. Oral Med. Oral Pathol. Oral Radiol. Endod . 94 , 515–521. 10.1067/moe.2002.126697 (2002). Segami, N. et al. Does joint effusion on T2 magnetic resonance images reflect synovitis? Comparison of arthroscopic findings in internal derangements of the temporomandibular joint. Oral Surg. Oral Med. Oral Pathol. Oral Radiol. Endod . 92 , 341–345. 10.1067/moe.2001.117808 (2001). Kopp, M. et al. MRI of Temporomandibular Joint Disorders: A Comparative Study of 0.55 T and 1.5 T MRI. Invest. Radiol. 59 , 223–229. 10.1097/RLI.0000000000001008 (2024). Ucar, I. et al. Is scoliosis related to mastication muscle asymmetry and temporomandibular disorders? A cross-sectional study. Musculoskelet. Sci. Pract. 58 , 102533. 10.1016/j.msksp.2022.102533 (2022). Bakhshayesh, P., Zaghloul, A., Sephton, B. M. & Enocson, A. A novel 3D technique to assess symmetry of hemi pelvises. Sci. Rep. 10 , 18789. 10.1038/s41598-020-75884-y (2020). Tan, C. K. et al. Lateral Symmetry of Synergies in Lower Limb Muscles of Acute Post-stroke Patients After Robotic Intervention. Front. Neurosci. 12 , 276. 10.3389/fnins.2018.00276 (2018). Ren, Y. F., Isberg, A. & Westesson, P. L. Condyle position in the temporomandibular joint. Comparison between asymptomatic volunteers with normal disk position and patients with disk displacement. Oral Surg. Oral Med. Oral Pathol. Oral Radiol. Endod . 80 , 101–107. 10.1016/s1079-2104(95)80025-5 (1995). Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 14 Nov, 2025 Read the published version in Scientific Reports → Version 1 posted Editorial decision: Revision requested 17 Jun, 2025 Reviews received at journal 08 Jun, 2025 Reviews received at journal 31 May, 2025 Reviewers agreed at journal 30 May, 2025 Reviewers agreed at journal 29 May, 2025 Reviewers agreed at journal 29 May, 2025 Reviewers invited by journal 29 May, 2025 Editor assigned by journal 29 May, 2025 Editor invited by journal 29 May, 2025 Submission checks completed at journal 28 May, 2025 First submitted to journal 27 May, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6756792","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":464609608,"identity":"93e0820d-cfb6-40d2-9c38-61a97dfdb975","order_by":0,"name":"Muhammed Enes Naralan","email":"data:image/png;base64,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","orcid":"","institution":"Recep Tayyip Erdoğan University","correspondingAuthor":true,"prefix":"","firstName":"Muhammed","middleName":"Enes","lastName":"Naralan","suffix":""},{"id":464609613,"identity":"cabee1db-1c50-4092-8666-40b0816f956f","order_by":1,"name":"Binali Çakır","email":"","orcid":"","institution":"Atatürk University","correspondingAuthor":false,"prefix":"","firstName":"Binali","middleName":"","lastName":"Çakır","suffix":""}],"badges":[],"createdAt":"2025-05-27 07:53:17","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6756792/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6756792/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41598-025-23800-7","type":"published","date":"2025-11-14T15:58:41+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":83897138,"identity":"b1154e71-9fde-4c3d-9c17-5ee7119a6059","added_by":"auto","created_at":"2025-06-04 08:55:44","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":153066,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eVector-based angular measurement of the temporomandibular joint (TMJ) on axial MRI.\u003c/strong\u003e\u003cbr\u003e\n(A) Axial T2-weighted MR image showing the anatomical landmarks used in coordinate-based vector analysis. The origin and insertion points of the lateral pterygoid muscle (LPM), as well as the medial and lateral poles of the condyle, are marked and labeled with their respective pixel coordinates: origin of LPM (x1, y1), insertion of LPM (x2, y2), medial condylar pole (x3, y3), lateral condylar pole (x4, y4), and the projected reference point (x4, y3). A 512×512 coordinate grid is superimposed to ensure spatial accuracy in angular measurement.\u003cbr\u003e\n(B) Schematic representation of the angular relationships. The lateral pterygoid muscle attachment angle is defined between the LPM vector and the condylar axis, while the condylar position angle is measured between the condylar axis and the reference plane. This vector-based approach allows for precise and reproducible evaluation of angular changes in TMJ structures.\u003c/p\u003e","description":"","filename":"Picture1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6756792/v1/ccb1d4e751ec22c0b69e1be7.jpg"},{"id":96105147,"identity":"0865ad40-d809-43d1-b92e-bc09e0b4c2f9","added_by":"auto","created_at":"2025-11-17 16:09:20","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1068074,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6756792/v1/a439557d-ce4c-4f67-8b01-f3f3f54e8112.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Angular Evaluation of the TMJ Using Axial MRI: Vector-Based Analysis of Condylar and Lateral Pterygoid Angles in Anterior Disc Displacement","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe temporomandibular joint (TMJ) is a diarthrodial joint formed by the mandibular condyle and the mandibular fossa of the temporal bone, playing a key role in essential functions such as chewing, speaking, and swallowing. The stability and mobility of this joint are closely related to surrounding tissues, particularly the function of the lateral pterygoid muscle (LPM). \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e The LPM is primarily responsible for mandibular protrusion and lateral deviation, as well as assisting in mouth opening. \u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e This muscle has two heads: the superior head attaches to the articular disc and capsule to ensure disc stability, while the inferior head functions in mandibular opening and protrusion. \u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eAmong temporomandibular joint disorders (TMD), anterior disc displacement (ADD) is one of the most frequently encountered pathologies. \u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e,\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e ADD is characterized by anterior displacement of the articular disc relative to the condyle, which may result in joint pain, limited mouth opening, and chewing difficulty. \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e ADD is classified into two main types: anterior disc displacement with reduction (ADDwR) and anterior disc displacement without reduction (ADDwoR).\u003c/p\u003e \u003cp\u003eIn particular, in long-standing and untreated cases of ADD, notable morphological changes occur in the condyle and articular disc. \u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e,\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e Prolonged condylar displacement may lead to the condyle repositioning within a new fossa, and during this process, changes such as fibrosis within the joint, perforation in retrodiscal tissues, and cartilage degeneration can be observed. \u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e,\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eThe LPM exhibits significant morphological and functional alterations depending on the presence and duration of ADD. In short-term conditions, hypertrophy may occur as a compensatory mechanism to maintain joint stability; whereas in chronic ADD cases, atrophy, fat infiltration, and fibrosis become prominent. \u003csup\u003e\u003cspan additionalcitationids=\"CR10\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e These pathological changes in the LPM are associated with reduced functional capacity and increased intramuscular heterogeneity. \u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e,\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e Several studies have reported notable atrophy and increased T1 signal intensity in the LPM, particularly in ADDwR cases. \u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e,\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eBiomechanical factors play a crucial role in the functional stability of the TMJ. The relationship between muscle force and joint angle is a critical element in the regulation of TMJ movement. \u003csup\u003e\u003cspan additionalcitationids=\"CR14\" citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e As the angle between the direction of muscle pull and the position of the condyle increases, the risk of anterior disc displacement rises. \u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e,\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e,\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e In particular, hypertonicity of the superior head of the LPM has been identified as a major contributing factor in the development of ADD. \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e While previous studies have indicated that alterations in joint angles may contribute to disc displacement, few have quantitatively evaluated the angular relationship between the lateral pterygoid muscle vector and condylar position in vivo.\u003c/p\u003e \u003cp\u003eAmong imaging modalities, magnetic resonance imaging (MRI) is considered the most reliable method for evaluating the soft tissue structures of the TMJ. \u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e,\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e MRI allows for detailed assessment of disc position, condylar morphology, and structural changes in the LPM, such as fat infiltration, atrophy, and fibrosis.\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e,\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e Among MRI planes, axial slices provide the most reliable visualization of the lateral pterygoid muscle\u0026rsquo;s orientation and its attachment to the condyle, allowing for accurate vector-based angular assessment.\u003c/p\u003e \u003cp\u003eMathematical methods such as the dot product can be used to calculate angular relationships between the muscle and the condyle. \u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e,\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e By utilizing pixel-based positional data, the angle between two vectors can be reliably calculated. This makes it possible to quantify angular changes between the pulling direction of the LPM and the position of the condyle, thus revealing the role of these changes in the development of ADD. \u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e,\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e This method can numerically demonstrate both alterations in the LPM\u0026rsquo;s direction of pull and changes in condylar position. Hence, it enables direct measurement of the impact of muscle and joint biomechanics on the pathogenesis of ADD.\u003c/p\u003e \u003cp\u003eIn this retrospective study, the LPM attachment angle and condylar position angle values in healthy individuals were established, and changes in these angles in patients with ADD were evaluated. We hypothesized that patients with ADD would show a decreased condylar position angle and possible changes in the LPM attachment angle, with variations depending on ADD subtype.\u003c/p\u003e \u003cp\u003eThe aim of this study is to evaluate, through an MRI-based vectorial analysis, the changes in the LPM attachment angle and condylar position angle in individuals with ADD, and to explore the potential relationship between these angles and the development of ADD.\u003c/p\u003e"},{"header":"Material method","content":"\u003cp\u003eThis study was approved by the Non-Interventional Ethics Committee of Recep Tayyip Erdoğan University (2025/86) and was conducted in accordance with the principles of the Declaration of Helsinki. As the study had a retrospective design, the requirement for informed consent was waived by the ethics committee.\u003c/p\u003e\n\u003cp\u003eThe research was carried out in the Departments of Oral and Maxillofacial Radiology at the Faculties of Dentistry of Recep Tayyip Erdoğan University and Atat\u0026uuml;rk University. Patients who underwent MRI examinations for temporomandibular joint disorders between September 1, 2022, and January 1, 2025, were included. Clinical records were reviewed to confirm that imaging was requested primarily for joint-related complaints rather than incidental findings.\u003c/p\u003e\n\u003cp\u003eInclusion criteria for MRI images consisted of images oriented such that axial planes were parallel to the ground, sagittal planes were perpendicular to the ground, and coronal planes were perpendicular to the sagittal plane. Radiologically healthy individuals and patients diagnosed solely with ADD were included. Radiologically healthy individuals (no disc displacement or osseous pathology) and patients diagnosed exclusively with ADD, based on MRI criteria, were included. Patients with systemic diseases, abnormal bony changes, arthritis, or other joint pathologies, as well as those with artifacts or positioning errors on MRI, were excluded.\u003c/p\u003e\n\u003cp\u003eMRI images used in the study were obtained using 1.5 Tesla Siemens Magnetom Aera, 1.5 Tesla Siemens Magnetom Avanto, and 3 Tesla Siemens Magnetom Skyra systems (Siemens Medical Systems, Erlangen, Germany). The imaging protocol included T1-weighted and T2-weighted sequences. T1-weighted sequences were acquired with a repetition time (TR) ranging from 7 to 8.6 ms and an echo time (TE) between 2.95 and 4 ms. T2-weighted sequences had TR values up to 3500 ms and TE values up to 120 ms (in specific sequences not used for angular measurement). Slice thickness varied between 3 and 5 mm, and all images were obtained with a 512\u0026times;512 matrix and field of view (FOV) between 250\u0026ndash;260 mm. No contrast agent was administered.\u003c/p\u003e\n\u003cp\u003eADD assessment was performed using parasagittal T1 and T2 sequences. In the closed-mouth position, if the articular disc exceeded\u0026thinsp;+\u0026thinsp;10\u0026deg; anterior to the 12 o\u0026apos;clock position of the condyle, it was considered indicative of ADD.⁶ In the open-mouth position, re-establishment of the disc over the condyle was classified as ADDwR, while failure to reposition was classified as ADDwoR.\u003c/p\u003e\n\u003cp\u003eCoordinate determination and angular measurements were performed on axial MRI slices using a pixel-based coordinate system. Analyses were conducted using the MicroDicom DICOM Viewer (MicroDicom Ltd, Sofia, Bulgaria). The evaluation was performed on the axial slice where the LPM was most prominently visible. The origin point of the muscle (x1, y1) was marked as the starting point, and the insertion point (x2, y2) was defined as the midpoint where the muscle attaches to the condyle. The medial and lateral poles of the condyle were marked at coordinates (x3, y3) and (x4, y4), respectively, in the slice where the condyle appeared widest. This pixel-based coordinate plane enabled precise measurements at the smallest units of the image, and all measurements were performed using this system. This coordinate-based measurement process is illustrated in Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e, which demonstrates the anatomical landmarks and vector orientations used for angular calculations.\u003c/p\u003e\n\u003cp\u003eTo assess the position of the condyle and establish a standard reference plane, a perpendicular projection from the lateral pole of the condyle (x4, y4) to the coronal plane was created in the axial slice where the condyle was widest. The projection point was defined by combining the x-coordinate of the lateral pole with the y-coordinate of the medial pole, creating a reference point at (x4, y3). In this study, the reference plane was defined by the vector between this projection point (x4, y3) and the medial pole of the condyle (x3, y3). Orientation and angular measurements were standardized based on this reference vector. This method ensured consistency in measuring the condyle\u0026rsquo;s position relative to a fixed reference plane.\u003c/p\u003e\n\u003cp\u003eTwo primary angular measurements were conducted: the LPM angle (angle formed between the muscle and the condyle) and the condylar position angle (angle between the condyle and the coronal plane).\u0026sup1;⁹ The dot product method was used to calculate the angles between two vectors, using the following formula:\u003c/p\u003e\n\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e$$\\:{\\theta\\:}=\\text{arccos}\\left(\\frac{\\left({x}_{2}-{x}_{1}\\right)\\cdot\\:\\left({x}_{4}-{x}_{3}\\right)+\\left({y}_{2}-{y}_{1}\\right)\\cdot\\:\\left({y}_{4}-{y}_{3}\\right)}{\\sqrt{{\\left({x}_{2}-{x}_{1}\\right)}^{2}+{\\left({y}_{2}-{y}_{1}\\right)}^{2}}\\cdot\\:\\sqrt{{\\left({x}_{4}-{x}_{3}\\right)}^{2}+{\\left({y}_{4}-{y}_{3}\\right)}^{2}}}\\right)$$\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eAngular measurements were calculated using the dot product, which provides the cosine of the angle between two vectors and ensures consistent directional assessment within the coordinate system. All coordinates were recorded at the pixel level, ensuring high-resolution measurement accuracy.\u003c/p\u003e\n\u003cp\u003eThe orientations of the vectors between the muscle and condyle were determined relative to this reference plane, and all measurements were conducted by a single dentomaxillofacial specialist (M.E.N). To assess measurement reliability, repeated measurements were performed on 25% of randomly selected cases. To evaluate intra-observer reliability, intraclass correlation coefficient (ICC) values with 95% confidence intervals were calculated using a two-way random-effects model (absolute agreement, single measurement). The obtained coordinate data were processed using formulas in Office 360 Excel (Microsoft, Seattle, USA) and used in statistical analyses.\u003c/p\u003e\n\u003cp\u003eStatistical analysis was performed using SPSS 29.0 (IBM Corp., Armonk, NY, USA). The distribution characteristics of continuous variables were evaluated using the Kolmogorov-Smirnov and Shapiro-Wilk normality tests. Since the data were not normally distributed, non-parametric test methods were employed. Differences between right and left sides in healthy individuals were evaluated with the Wilcoxon test, and comparisons between groups were made using the Kruskal-Wallis H test. For variables with significant differences according to the Kruskal-Wallis test, the Post-hoc Dunn test was applied to identify which groups were responsible for the differences. The Mann-Whitney U test was used for comparisons based on sex. A p-value of \u0026lt;\u0026thinsp;0.05 was considered statistically significant for all analyses.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eA total of 151 patients and 302 TMJs were included in this study. The study sample included 115 females (76.2%) and 36 males (23.8%), with a mean age of 38.9\u0026thinsp;\u0026plusmn;\u0026thinsp;12.4 years.\u003c/p\u003e \u003cp\u003eWhen evaluating the joints included in the study, Of the 302 joints evaluated, 144 (47.7%) were classified as healthy, 110 (36.4%) as ADDwR, and 48 (15.9%) as ADDwoR.\u003c/p\u003e \u003cp\u003eIntra-observer reliability was assessed using the ICC based on a two-way random-effects model, single-measurement, absolute agreement. Intra-observer reliability was excellent, with ICC values of 0.965 (95% CI: 0.943\u0026ndash;0.981) for the LPM angle and 0.969 (95% CI: 0.948\u0026ndash;0.984) for the condylar angle. \u0026sup2;\u0026sup1;\u003c/p\u003e \u003cp\u003eFor the LPM attachment angle, the median value for the left joint was 69.43\u0026deg; (min: 41.64\u0026deg;, max: 83.18\u0026deg;), with a mean of 68.30\u0026deg; \u0026plusmn; 8.79\u0026deg;. For the right joint, the median value was 70.20\u0026deg; (min: 46.27\u0026deg;, max: 177.52\u0026deg;), with a mean of 75.10\u0026deg; \u0026plusmn; 26.31\u0026deg;.\u003c/p\u003e \u003cp\u003eRegarding the condylar angle, the median value for the left joint was 159.12\u0026deg; (min: 137.07\u0026deg;, max: 179.99\u0026deg;), with a mean of 159.18\u0026deg; \u0026plusmn; 7.95\u0026deg;. For the right joint, the median value was 157.69\u0026deg; (min: 145.01\u0026deg;, max: 179.84\u0026deg;), with a mean of 159.49\u0026deg; \u0026plusmn; 7.93\u0026deg;.\u003c/p\u003e \u003cp\u003eTo evaluate whether there were statistical differences in measurements of healthy joints between genders, the Mann-Whitney U test was used. The p-value for the LPM attachment angle was found to be 0.163, indicating no statistically significant difference between male and female patients. Similarly, the p-value for the condylar position angle was calculated as 0.104, showing no significant difference between genders. These findings indicate that sex does not significantly affect the LPM attachment angle or condylar position angle in healthy individuals.\u003c/p\u003e \u003cp\u003eWhen the LPM attachment angle and condylar position angle in healthy individuals were evaluated using the Wilcoxon test, no significant difference was observed between the right and left joints. These findings suggest that angular symmetry is maintained between the right and left TMJs in healthy individuals, supporting the anatomical consistency of the measurement method.\u003c/p\u003e \u003cp\u003eAccording to the results of the Kruskal-Wallis test, there was no statistically significant difference in LPM attachment angle among the groups (p\u0026thinsp;=\u0026thinsp;0.51). This result confirms that LPM attachment angle does not significantly differ across the three groups, including healthy, ADDwR, and ADDwoR. On the other hand, analysis of the condylar position angle revealed a significant difference among the groups (p\u0026thinsp;=\u0026thinsp;0.01), suggesting a potential relationship between condylar position and the presence of ADD. Notably, the condylar angle in the ADDwoR group was lower compared to healthy individuals. (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e)\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eLPM Attachment Angle and Condylar Position Angle Across Groups with Kruskal-Wallis Test Results\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003en\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMedian LPM Attachment Angle(Min.\u0026ndash;Max.)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMedian Condylar Position Angle (Min.\u0026ndash;Max.)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eLPM Attachment Angle Group \u003cem\u003ep\u003c/em\u003e-Value\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eCondylar Angle Group \u003cem\u003ep\u003c/em\u003e-Value\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHealthy\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e144\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e69.42\u003c/p\u003e \u003cp\u003e(41.64\u0026ndash;177.52)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e158.72 (137.07\u0026ndash;179.99)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e0.51\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e\u003cb\u003e0.01*\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eADDwR\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e110\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e68.30\u003c/p\u003e \u003cp\u003e(31.77\u0026ndash;178.03)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e157.27 (140.53\u0026ndash;177.45)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eADDwoR\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e48\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e70.68 (50.08\u0026ndash;143.14)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e155.59 (133.10\u0026ndash;177.89)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e\n\u003ch3\u003e* Indicates statistical significance based on Kruskal-Wallis test results\u003c/h3\u003e\n\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eADDwR: Anterior disc displacement with reduction\u003c/h2\u003e \u003cdiv id=\"Sec6\" class=\"Section3\"\u003e \u003ch2\u003eADDwoR: Anterior disc displacement without reduction\u003c/h2\u003e \u003cdiv id=\"Sec7\" class=\"Section4\"\u003e \u003ch2\u003eLPKA: Lateral pterygoid muscle attachment angle\u003c/h2\u003e \u003cp\u003eAccording to the results of the post-hoc Dunn test, a statistically significant difference in condylar position angle was found between healthy individuals and both ADDwR and ADDwoR patients. The p-value for the difference between the healthy group and the ADDwR group was calculated as 0.01, and the p-value for the difference between the healthy group and the ADDwoR group was also 0.01. On the other hand, no significant difference was observed between the ADDwR and ADDwoR groups (p\u0026thinsp;=\u0026thinsp;0.46). Although ADD was associated with a significantly reduced condylar angle compared to healthy joints, no significant difference was observed between ADDwR and ADDwoR, suggesting that disc reduction status does not substantially influence this angular change. (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e)\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSignificance Levels of Condylar Position Angle Within Groups According to Post-hoc Dunn Test\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eComparison\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003en\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cem\u003ep\u003c/em\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHealthy vs. ADDwR\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e144\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e0.01*\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHealthy vs. ADDwoR\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e110\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e0.01*\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eADDwR vs. ADDwoR\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e48\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.46\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e* Indicates statistical significance based on post-hoc Dunn test results\u003c/h2\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003eADDwR: Anterior disc displacement with reduction\u003c/h2\u003e \u003cdiv id=\"Sec10\" class=\"Section4\"\u003e \u003ch2\u003eADDwoR: Anterior disc displacement without reduction\u003c/h2\u003e \u003cp\u003eTo further detail the differences between groups, the Mann-Whitney U test was applied. This test was conducted to determine whether there were statistically significant differences in LPM attachment angle and condylar position angle among healthy individuals, ADDwR patients, and ADDwoR patients.\u003c/p\u003e \u003cp\u003eAccording to the results, no statistically significant differences were found in any of the comparisons regarding the LPM attachment angle (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05). Although no statistically significant difference was found, the median LPM angle values were slightly higher in healthy individuals compared to the ADDwR and ADDwoR groups. (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e)\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMann-Whitney U Test Results: Intergroup Comparisons of LPM Attachment Angle and Condylar Position Angle\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eComparison\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMedian Difference\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eU Value\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cem\u003ep\u003c/em\u003e-Value\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eDirection of Difference (Higher Value)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eLateral Pterygoid Muscle Attachment Angle\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eHealthy vs. ADDwR\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1,36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e8765\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0,14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eHealthy\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eHealthy vs. ADDwoR\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0,01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3416\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0,90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eHealthy\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eADDwR vs. ADDwoR\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-1,35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2300\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0,19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eADDwoR\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eCondylar Position Angle\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eHealthy vs. ADDwR\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1,70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e8212\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0,61\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eHealthy\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eHealthy vs. ADDwoR\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2,26\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3897\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0,18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eHealthy\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eADDwR vs. ADDwoR\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0,55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2909\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0,31\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eADDwR\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eADDwR: Anterior disc displacement with reduction\u003c/h2\u003e \u003cdiv id=\"Sec12\" class=\"Section3\"\u003e \u003ch2\u003eADDwoR: Anterior disc displacement without reduction\u003c/h2\u003e \u003cp\u003eStatistically significant differences in condylar position angle were observed between healthy individuals and both ADD groups (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). However, no significant difference was found between the ADDwR and ADDwoR groups. Overall, the condylar angle tended to be greater in healthy individuals.\u003c/p\u003e \u003cp\u003eThese findings suggest that changes in condylar position angle may be associated with anterior disc displacement. However, whether the ADD is with or without reduction does not appear to be a determining factor for the condylar position.\u003c/p\u003e \u003cp\u003eRegarding the LPM attachment angle, no statistically significant difference was observed among the groups. Nonetheless, when the direction of the difference was examined, it was noted that the mean LPM angle was higher in healthy individuals.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eOur findings confirm that anterior disc displacement is associated with changes in condylar positioning, while LPM angular orientation appears unaffected. While the condylar position angle showed a significant change, the LPM attachment angle did not exhibit a meaningful difference. This contrast suggests that structural remodelling in the joint may occur independently of measurable angular changes in muscle orientation.\u003c/p\u003e \u003cp\u003eIn this study, no statistically significant differences were found between genders in terms of LPM attachment angle or condylar position angle. This finding is consistent with existing literature suggesting that gender does not have a marked effect on TMJ biomechanics. \u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e,\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e While Melke et al. \u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e reported that LPM volume is greater in males than in females, our study did not detect a significant angular difference between genders. The lack of angular difference between gneders contrasts with reports of LPM volume differences. This discrepancy may be due to differences in measurement parameters or sample composition, particularly the female-dominated cohort.\u003c/p\u003e \u003cp\u003eThe dot product method used for measurements in this study is consistent with other coordinate system approaches recommended in the literature for calculating joint angles. \u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e,\u003cspan additionalcitationids=\"CR24\" citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e In particular, Van Hauwermeiren et al. \u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e proposed a standardized coordinate system to more objectively represent the biomechanical data of joints. This system, which is aligned with joint surfaces, provides high ICC values and enhances measurement consistency in complex geometric structures such as the TMJ. The high ICC values (0.965\u0026ndash;0.969) indicate excellent intra-observer reliability, supporting the consistency of the coordinate-based method used.\u003c/p\u003e \u003cp\u003eMRI is the gold standard for TMJ evaluation due to its superior soft tissue contrast and absence of radiation exposure \u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e,\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e,\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e Although sagittal slices are commonly used to assess disc position and anterior-posterior condylar movement \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e they are limited in evaluating the orientation of the LPM. Since the LPM primarily operates in the anteroposterior plane, axial slices provide clearer visualization of its attachment and directional vector \u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e,\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e,\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e,\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e,\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e Therefore, in this study, angular measurements were performed on axial slices, which offer a broader field of view for assessing both LPM orientation and mediolateral condylar deviations.\u003c/p\u003e \u003cp\u003eAll MRI systems used in this study had field strengths\u0026thinsp;\u0026ge;\u0026thinsp;1.5T, which are widely accepted in the literature as sufficient for joint and muscle evaluation. \u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eSince the imaging methods were limited to two-dimensional (2D) axial slices, the spatial detail that could be provided by three-dimensional (3D) evaluations could not be obtained. In the literature, 3D imaging has been reported to enable a more accurate and comprehensive assessment of TMJ biomechanics. \u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e,\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e From a clinical perspective, this limitation may have prevented a complete depiction of the three-dimensional spatial relationship between the muscle and the condyle. Despite the absence of 3D imaging, the anteroposterior orientation of the LPM justifies the use of axial 2D slices for this angular analysis. The literature emphasizes that the primary function of the LPM is to advance the mandible and maintain anteroposterior stability of the articular disc, and that the anteroposterior movement of the muscle plays a more decisive role in TMJ biomechanics.\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e Clinically, the fact that the LPM's main pulling direction is anteroposterior made it more meaningful for this study to focus on anteroposterior angles. Future imaging studies should examine the three-dimensional movement patterns of the muscle in greater detail to better reflect them in clinical applications.\u003c/p\u003e \u003cp\u003eIn presented study, no statistically significant difference was observed between the right and left TMJ structures. This finding aligns with the expected right-left symmetry in craniofacial anatomy. It also underscores the importance of the measurement method used in this study, demonstrating that it is both unbiased and anatomically consistent. Symmetry analyses conducted in different anatomical regions in the literature also support this outcome. For example, in a study evaluating the volume of the masseter muscle, no significant difference was found between the right and left sides in either individuals with scoliosis or control subjects. \u003csup\u003e\u003cem\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/em\u003e\u003c/sup\u003e Similarly, Bakhshayesh et al. used 3D imaging and volume fusion techniques to assess pelvic structures and reported that the right and left hemipelvis were clinically symmetrical in healthy individuals. \u003csup\u003e\u003cem\u003e\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/em\u003e\u003c/sup\u003e At the muscular function level, Tan et al.\u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e showed that muscle synergies became more symmetrical between sides in patients undergoing robotic rehabilitation after stroke, and that this improvement developed alongside motor recovery. Additionally, Ren et al.\u003csup\u003e\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e, analyzed and found a high degree of similarity in movement patterns between the right and left extremities in healthy individuals, while noting that this symmetry was disrupted in neurodegenerative diseases. All these findings suggest that the absence of side-to-side differences in our study is not only a physiologically expected result, but also an indicator of the validity of the method used.\u003c/p\u003e \u003cp\u003eIn this study, a statistically significant change in condylar position angle was detected in patients with ADD (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). In the study by Wadhawan et al. \u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e, it was reported that in patients with ADD, the condyle was positioned more posteriorly and superiorly, and that this adaptive change led to angular alterations in joint biomechanics. Similarly, in the study by Manfredini et al. \u003csup\u003e\u003cb\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/b\u003e\u003c/sup\u003e it was emphasized that hyperactivity of the LPM contributed to changes in condylar position. The observed decrease in condylar position angle among ADD patients supports prior findings of joint remodelling and posterior-superior displacement of the condyle in chronic cases.\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e The lower condylar angle observed particularly in ADDwoR patients indicates that compensatory changes may have occurred in the joint, potentially affecting joint function. The literature reports that in prolonged condylar displacements, fibrotic structures may form in an effort to increase joint stability, resulting in the condyle being fixed in a new position. \u003csup\u003e\u003cb\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/b\u003e\u003c/sup\u003e The findings of this study demonstrate the adaptive changes occurring in the condyles of patients with ADD.\u003c/p\u003e \u003cp\u003eThe observed decrease in condylar position angle in both ADDwR and ADDwoR groups raises the question of whether this angular change is a contributing factor to disc displacement or a result of chronic adaptation. While some studies have suggested that altered condylar orientation may precede disc displacement and facilitate its development through biomechanical misalignment \u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e, others have reported that prolonged disc displacement can cause remodelling and posterior-superior condylar shift as a secondary outcome \u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e. Given the cross-sectional nature of our study, causality cannot be established. However, the angular difference observed in both ADD subtypes\u0026mdash;even in the absence of reduction\u0026mdash;suggests that remodelling may play a larger role in shaping joint biomechanics over time.\u003c/p\u003e \u003cp\u003eIt has also been noted that this adaptation mechanism may limit joint mobilization in non-surgical treatments.⁸ This finding represents an important factor that should be considered in maintaining joint stability and planning treatment. It is suggested that conservative treatment approaches applied during the early stages of ADD may be more effective before morphological changes occur in the joint. In contrast, in advanced ADDwoR patients, biomechanical alterations within the joint may limit the success of non-surgical treatment approaches.\u003c/p\u003e \u003cp\u003eIn the study by Shahab et al.\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e it was shown that a condylar horizontal angle greater than 30\u0026deg; was associated with ADD, and that the intercondylar angle was smaller in patients with ADD. In our study, while no statistically significant difference was found in the LPM attachment angle, the condylar position angle was found to be associated with ADD. This discrepancy suggests that the angular parameters assessed may influence joint biomechanics in different ways. The study by Shahab et al. \u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e focused on macro-level changes in condylar and joint mechanics, whereas our study evaluated the local effects of the LPM attachment angle.\u003c/p\u003e \u003cp\u003eThe study by Ren et al. \u003csup\u003e\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e demonstrated that maintaining a stable disc position does not lead to significant morphological changes in the disc. When the disc remains in a stable position, it may not induce morphological changes in the LPM either, as the muscle\u0026rsquo;s requirement for active contraction is reduced. In contrast, the study by Ngamsom et al. \u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e reported that in ADDwoR patients, the disc remains fixed in an anterior position, allowing the condyle to acquire a stable position as well, resulting in minimal angular differences.\u003c/p\u003e \u003cp\u003eIn current study, no statistically significant difference was found in the LPM attachment angle across groups. This result may be explained by two complementary factors: \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e the possibility of muscle adaptation in long-term ADD, where angular orientation remains stable despite internal structural changes (such as atrophy or fibrosis); and \u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e the limitations of 2D MRI, which may fail to capture the full spatial orientation of the muscle. This suggests that while the LPM undergoes morphological changes in ADD, these may not always translate into measurable angular deviations on standard axial imaging.\u003c/p\u003e \u003cp\u003eThe findings of our study are consistent with these explanations in the literature. No significant difference in condylar position angle was found between ADDwR and ADDwoR patients. This finding suggests that whether ADD is with or without reduction may result in similar biomechanical outcomes in the joint. Similarly, the literature indicates that in the advanced stages of ADD, the condyle and articular disc may transition into a new stable position, leading to structural changes in the joint becoming fixed over time. \u003csup\u003e\u003cb\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/b\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eThe literature indicates that the LPM undergoes significant morphological and functional changes in patients with ADD. In the study by Wang et al. \u003csup\u003e\u003cem\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/em\u003e\u003c/sup\u003e, increased severity of ADD was associated with fat infiltration and greater muscle heterogeneity in the LPM. These changes were reported to be especially prominent in the ADDwoR group and were linked to long-term dysfunction. The study by Ngamsom et al. \u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e also reported alterations in the superior head of the LPM, including hypertrophy, atrophy, and contracture. The role of LPM hyperactivity in the pathogenesis of ADD is further supported by the study of Manfredini et al. \u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eThe lack of angular differences in the LPM may stem from the limitations of 2D imaging, which cannot fully capture the complexity of muscle orientation. Moreover, long-term disc displacement could lead to muscular adaptation that preserves angular alignment despite internal changes.\u003c/p\u003e \u003cp\u003eThe role of the LPM in the development of ADD has been addressed in various studies in the literature. For instance, some studies suggest that hyperactivity of the LPM may trigger the development of ADD, while others indicate that it may contribute to joint stability. In the study by Wang et al. \u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e, it was reported that in the advanced stages of ADD, fat infiltration and atrophy occur in the LPM, leading to reduced muscle function. In the study by Ngamsom et al. \u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e, no direct correlation was found between LPM hyperactivity and pathological changes in the joint. This may be another factor that explains why no significant difference was observed in the LPM angle in our study.\u003c/p\u003e \u003cp\u003eThe relationship between the LPM and anterior disc displacement has been addressed in numerous studies in the literature. In the study by Wang et al. \u003csup\u003e\u003cb\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/b\u003e\u003c/sup\u003e, it was reported that the LPM undergoes functional changes in conjunction with disc displacement; however, these changes could not be definitively correlated with angular parameters. Similarly, in the study by Liu et al.\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e, significant structural changes in the LPM were observed in the presence of ADD, but no direct association with angular measurements could be established.\u003c/p\u003e \u003cp\u003eThis does not imply a complete rejection of the hypothesis. The hypothesis that the LPM angle plays an important role in the development of ADD should be reconsidered considering factors such as compensatory adaptation of the muscle, varying patterns of muscle activity across different stages of the disorder, and methodological limitations. Particularly in advanced stages of ADD, the biomechanical function of the LPM may change, which could be reflected in its angular position. Furthermore, the low sample size in the ADDwoR group may have limited the detection of statistical differences. This may have contributed to the lack of significant findings in LPM attachment angle comparisons.\u003c/p\u003e \u003cp\u003eThis study offers a reproducible angular measurement approach for TMJ evaluation, though further validation with functional and 3D data is required to establish clinical utility. By applying a pixel-based vectorial analysis, it provides a reproducible method for evaluating angular changes in TMJ structures. While the approach shows promise for future studies, additional validation and functional correlations are needed to support its broader clinical application.\u003c/p\u003e \u003cp\u003eThis study has several limitations. First, the angular measurements were derived from two-dimensional MRI slices, which may not fully represent the three-dimensional dynamics of the lateral pterygoid muscle. Second, no functional assessments such as electromyography were performed to evaluate the muscle\u0026rsquo;s activity directly. Third, all measurements were conducted by a single observer. Although intra-observer reliability was excellent, the lack of inter-observer validation limits the generalizability of the results. Future studies should incorporate dynamic imaging and multi-observer analysis to validate and expand upon the current findings.\u003c/p\u003e \u003cp\u003eIn future studies, the functional movements of the LPM should be examined in more detail, and the dynamic structure of the muscle should be evaluated with additional imaging methods. Considering morphological parameters such as fat infiltration, fibre composition, and volumetric changes will further contribute to shaping clinical approaches for a better understanding of the role of the muscle in the ADD process.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThe results of this study suggest a potential relationship between condylar position and anterior disc displacement, whereas no significant difference was found in muscle angle. These findings highlight the complexity of TMJ biomechanics and the need for comprehensive evaluation methods. The vector-based approach used here offers a reproducible technique for angular analysis, but further studies incorporating functional and three-dimensional assessments are required to confirm its clinical applicability.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eCompeting interests\u003c/h2\u003e \u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eNo funding.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eM.E.N. designed the study, performed the data collection and angular measurements, conducted the statistical analysis, and wrote the initial draft of the manuscript. B.\u0026Ccedil;. supervised the study, contributed to data interpretation, provided critical revisions, and approved the final version of the manuscript. All authors reviewed and approved the final manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThe authors would like to thank Dr. Y\u0026uuml;ksel S\u0026uuml;meyra Naralan for providing valuable support and guidance in the statistical analysis of the study. The authors used a generative large language model solely to assist with language refinement and proofreading. All scientific content, including data analysis, interpretation, and the final approval of the manuscript, was entirely conducted and validated by the authors.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe datasets generated and/or analysed during the current study are not publicly available due to patient privacy restrictions but are available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eOmami, G. \u0026amp; Lurie, A. 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Comparison between asymptomatic volunteers with normal disk position and patients with disk displacement. \u003cem\u003eOral Surg. Oral Med. Oral Pathol. Oral Radiol. Endod\u003c/em\u003e. \u003cb\u003e80\u003c/b\u003e, 101\u0026ndash;107. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/s1079-2104(95)80025-5\u003c/span\u003e\u003cspan address=\"10.1016/s1079-2104(95)80025-5\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (1995).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Temporomandibular joint, anterior disc displacement, lateral pterygoid muscle, condylar position, angular analysis, MRI, dot product","lastPublishedDoi":"10.21203/rs.3.rs-6756792/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6756792/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study aimed to investigate angular changes in the temporomandibular joint (TMJ) associated with anterior disc displacement (ADD) through axial magnetic resonance imaging (MRI). Specifically, the lateral pterygoid muscle (LPM) attachment angle and the condylar position angle were evaluated using a coordinate-based vector analysis method. A total of 151 patients and 302 TMJs were retrospectively evaluated. Joints were categorized into three groups: healthy, ADD with reduction (ADDwR), and ADD without reduction (ADDwoR). On axial MRI slices, angular measurements were obtained using a pixel-based coordinate system and calculated using the dot product method. Intra-observer reliability was assessed using intraclass correlation coefficients (ICCs). Measurement reliability was high (ICC\u0026thinsp;=\u0026thinsp;0.965 for LPM angle, ICC\u0026thinsp;=\u0026thinsp;0.969 for condylar angle). No significant differences were found in LPM angle between groups (p\u0026thinsp;=\u0026thinsp;0.51). In contrast, condylar position angle was significantly lower in both ADD groups compared to healthy joints (p\u0026thinsp;=\u0026thinsp;0.01). No statistically significant difference was observed between the ADDwR and ADDwoR groups. A significant decrease in condylar position angle was observed in joints affected by ADD, possibly indicating adaptive joint remodelling over time. However, no angular change was observed in the attachment angle of the lateral pterygoid muscle. The vector-based measurement method demonstrated high intra-observer reliability and may offer a reproducible approach for angular assessment of TMJ structures.\u003c/p\u003e","manuscriptTitle":"Angular Evaluation of the TMJ Using Axial MRI: Vector-Based Analysis of Condylar and Lateral Pterygoid Angles in Anterior Disc Displacement","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-06-04 08:55:40","doi":"10.21203/rs.3.rs-6756792/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-06-17T05:02:27+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-06-08T22:34:58+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-05-31T16:21:00+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"237586667178452985709176787634087116248","date":"2025-05-30T11:35:13+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"244034685796523140596337052223772984971","date":"2025-05-29T20:44:19+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"64120595431515343561652747695788835363","date":"2025-05-29T15:20:54+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-05-29T14:27:50+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-05-29T14:25:33+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-05-29T11:54:48+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-05-28T11:55:21+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2025-05-27T07:44:04+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"92d9aea1-8f3b-47d6-bc02-fb9e920b3f5b","owner":[],"postedDate":"June 4th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":49331669,"name":"Health sciences/Health care/Medical imaging/Magnetic resonance imaging"},{"id":49331670,"name":"Health sciences/Health care/Dentistry/Dental radiology"}],"tags":[],"updatedAt":"2025-11-17T16:04:15+00:00","versionOfRecord":{"articleIdentity":"rs-6756792","link":"https://doi.org/10.1038/s41598-025-23800-7","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2025-11-14 15:58:41","publishedOnDateReadable":"November 14th, 2025"},"versionCreatedAt":"2025-06-04 08:55:40","video":"","vorDoi":"10.1038/s41598-025-23800-7","vorDoiUrl":"https://doi.org/10.1038/s41598-025-23800-7","workflowStages":[]},"version":"v1","identity":"rs-6756792","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6756792","identity":"rs-6756792","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}