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Objective: to explore the association between the distance of disc displacement and disc morphology in patients with temporomandibular disorders (TMDs). Methods: a total of 717 joints in 473 subjects were enrolled in this cross-sectional study. The magnetic resonance imaging (MRI) of each patient was evaluated for temporomandibular joint (TMJ) disc morphology classification and position. The distance of the disc displacement and disc length were measured for smoothing spline prediction. A stratified analysis was performed based on the types of disc positions. The disc width and length-width ratio (L/W) were also measured. Descriptive statistics, one-way analysis of variance, smoothing spline analysis, threshold analysis, and two piecewise linear regression were performed to investigate the association between the displacement distance and length of discs. Results: the differences in displacement distance among morphological categories and among different disc positions were statistically significant. Nonlinear relationships were found between distance and length in all subjects. Two turning points of distance (−1.8 mm and 1.7 mm) were found, dividing the curve into three segments. Disc width and L/W were significantly different among discs in the three segments of the curve. The correlation coefficient (β) for the three segments were as follows: −0.6 [95% confidence interval (CI) = −0.9 to −0.3, p < 0.001], 0.0 (95% CI = −0.1 to 0.0, p = 0.027), and −0.7 (95% CI = −0.8 to −0.7, p < 0.001). Nonlinear relationships were also found between the distance and length in cases with anterior disc displacement (ADD), anterior disc displacement with reduction (ADDWR), and without reduction (ADDWoR). Conclusion: the turning points of the disc displacement distance may be considered as a potential reference value for high-risk disc deformation and ADD. Disc length decreases sharply with anterior disc displacement when the disc displacement distance is over 1.7 mm. Prospective and long-term studies are required to clarify the natural course of the disc at different stages of the regression curve. [ABSTRACT FROM AUTHOR]

Background: Temporomandibular joint osteoarthritis (TMJ‐OA) causes severe symptoms such as chewing difficulties, acute pain and even maxillofacial deformity. However, there is hardly any effective disease‐curing strategy because of uncertainty in aetiology. Animal model is an excellent tool to investigate the mechanism, prevention and treatment on diseases. Currently, although several TMJ‐OA animal models have been established, there are almost no comparative studies on different models, which poses a great challenge for selecting suitable models. Objective: To compare three TMJ‐OA induction methods and assess their applicability considering pathological changes in the cartilage, subchondral bone, osteoclasts, and synovium. Methods: Murine models were employed and followed for 3 and 6 weeks after experimental procedures (surgery, injection, crossbite). The TMJ changes were evaluated by Safranin‐O/Fast green staining, immunofluorescence staining, micro‐CT, TRAP staining, and HE staining. Results: In the Surgery group, a pronounced drop in bone volume fraction was observed. In the Injection group, chondrocytes were mostly disordered or arranged in clusters and a substantial increase in the OARSI score and osteoclasts was found. The OARSI score and osteoclasts also increased significantly in the Crossbite group, although to a lower extent compared with injection. Conclusion: Osteoarthritis‐like changes were observed in all models. Concerning the applicability of the different induction methods, surgery might be an important resource for the assessment of post‐traumatic TMJ‐OA and subchondral bone changes in early stages. Injection induces a severe end‐stage osteoarthritis in a short time and provides model basis for advanced TMJ‐OA. Crossbite might be more reasonable model to explore the pathogenesis mechanism of temporomandibular arthritis due to occlusal disorders. [ABSTRACT FROM AUTHOR]