Study design
To address the research purpose, the investigators designed and implemented a cross-sectional retrospective study. The study population was composed of all patients presenting for evaluation and management of TMJ ADD recruiting from the Temporomandibular Joint Specialist Clinic, The First Affiliated Hospital of Xinjiang Medical University, China, between March 2018 and May 2021. The study protocol was approved by the Ethics Committee of the Stomatological School of Xinjiang Medical University, The First Affiliated Hospital of Xinjiang Medical University (approval no. K202108-25) and followed the principles outlined in the Declaration of Helsinki. Informed consent was provided by all families. All data generated or analyzed during this study are included in this published article.
According to the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) [20], the diagnostic key points of ADD include the following: TMJ clicking sounds or noises during different time phases of opening and closing movements; various degrees of limitation in opening the mouth; mandible deflection when opening the mouth; and pain confined to the TMJ area at rest and during function.
Study sample
Inclusion criteria
The inclusion criteria were as follows: ADD with or without reduction that had not been treated previously; no history of infection, trauma, and tumor in the otic area or TMJ; ability to undergo plain and enhanced MRI examinations; high-resolution CBCT scan of the TMJ within 3 months of the MRI examination; and willingness to accept our medical treatment.
Exclusion criteria
Patients who met any of the following criteria were excluded: obvious organ dysfunction or organ failure; radiographic examination showed organic lesions in the TMJ; a history of osteoarthritis involved with the TMJ (e.g., juvenile idiopathic arthritis); congenital cranio-maxillo-facial anomalies (e.g., condylar hypertrophy) and/or any other TMJ disease; and contraindications for MRI and CBCT examinations.
MR image acquisition
A 3-Tesla system equipped with the multichannel transcranial magnetic stimulation/MRI head-neck coil array (MAGNETOM Aera; Siemens Healthineers, Erlangen, Germany) was used during the resting-state functional MRI examination of the bilateral TMJ without sedatives or intravenous contrast medium. The patient was kept in the supine position so that the Frankfurt horizontal plane was perpendicular to the table surface. Scanning was performed in the oblique sagittal (wide open and closed mouth), axial (wide open and closed mouth), and coronal (closed mouth) planes so that the projection angle was in line with Schüller’s position. Fast spin echo sequences using T1-weighted imaging, T2-weighted imaging, and proton density-weighted imaging generating contiguous sections of 20 axial slices, 15 coronal slices, and 18 sagittal slices, respectively, were used to evaluate different TMJ segments. The technical parameters for T1-weighted imaging, T2-weighted imaging, and proton density-weighted imaging, respectively, were as follows: repetition time (TR) = 700 ms, echo time (TE) = 10 ms, flip angle = 120°, field of view (FOV) = 25.6 cm × 25.6 cm, matrix = 256 × 256, number of acquisitions = 1, slice thickness = 2 mm, and slice gap = 0.2 mm; TR/TE = 5000 ms/92.5 ms, flip angle = 120°, FOV = 21 cm × 21 cm, matrix = 320 × 288, number of acquisitions = 2, slice thickness = 3 mm, and slice gap = 4 mm; and TR/TE = 3000 ms/64 ms, flip angle = 120°, FOV = 14 cm × 14 cm, matrix = 288 × 192, number of acquisitions = 2, slice thickness = 2 mm, and slice gap = 1 mm. All imaging protocols were identical for all patients. All magnetic resonance images were analyzed by two clinicians (a radiologist and an oral and maxillofacial specialist).
CBCT image acquisition
All patients underwent high-resolution CBCT of the TMJ under uniform conditions. A head positioner and cursor positioning system were used to position the midsagittal plane of the face of the patient vertical to the ground and the Frankfurt horizontal plane parallel to the ground. Patients remained immobile in the mandibular postural position (binocular smooth inspect facing forward, no chewing, no swallowing, no speaking, and the upper and lower dentitions naturally maintaining the intercuspal position) during the scanning procedure. The technical parameters were as follows: tube voltage, 85 kilovolt peak; effective tube current, 7 mA; thickness layer of the scanning process, 0.15 mm; reconstructed slice thickness, 0.625 mm; reconstructive interval, 0.5 mm; revolution speed, 1 s/rotation; and matrix, 512 × 512. The CBCT protocol included the GALILEOS® COMFORTPLUS (Sirona Dental Systems GmbH, Bensheim, Germany) unit with a FOV of 20 × 19 cm, isotropic voxels of 0.3 mm in the axial slice thickness, and 15 s of total scanning time (Additional file 1).
Processing of imaging materials and data measurements
A picture archiving and communication system workstation created the TMJ MRI data. All MRI performed using the DICOM format were processed using ImageJ software version 1.52 (National Institutes of Health, Bethesda, Maryland, USA) to classify the following three subtypes based on the TMJ disc location [21]: normal articular disc position (NADP); ADD with reduction (ADDwR); and ADD without reduction (ADDwoR) (Fig. 1A–E).
CBCT images were exported to the SIDEXIS XG Digital Radiography system (Sirona Dental Systems GmbH, Bensheim, Germany) and imported to Mimics software version 19.0 (Materialise Inc., Leuven, Belgium) for 3D plane reorientation and reconstruction. The 3D parameterized modeling was performed by reorienting every plane, setting the grayscale thresholds (226–3071 HU), determining the condyle boundary (Fig. 2A, B), completing 3D reconstruction of the condyle (Fig. 3A, B), and completing 3D reconstruction of the glenoid fossa (Fig. 4A–D).
Using the reconstructed 3D model, 3-matic Research software version 11.0 (Materialise Inc., Leuven, Belgium), Geomagic Wrap 2017 (64bit) (Raindrop 3D Systems Inc., Wilmington, North Carolina, USA), and Mimics software version 19.0 (Materialise Inc., Leuven, Belgium), the following 10 representative morphological parameters were calculated and output automatically through the above measuring softwares: condylar volume (CV); condylar superficial area (CSA); fossa volume (FV); fossa superficial area (FSA); the proportion of the condylar volume in the articular fossa (CV%); the proportion of the condylar superficial area in the articular fossa (CSA%). The definition of measured space is based on the spatial relationship between the condyle and the articular fossa. a. anterior joint space (AJS), the shortest distance between the front of condyle and the front of fossa; b. medial joint space (MJS), the shortest distance between the medial side of condyle and the medial side of fossa; c. posterior joint space (PJS), the shortest distance between the posterior side of condyle and the posterior side of articular fossa; d. superior joint space (SJS), the shortest distance from the uppermost point of the condyle to the articular fossa (Fig. 5A, B). Based on the reconstruction of condyle and fossa, the CV, CSA, FV, and FSA values were calculated and output automatically when double-clicked on the icon in display interface (Fig. 5C, D); and, correspondingly, the CV% value was evaluated using the following formula: CV% =|CVcondyle-CVfossa|÷ CVcondyle; the CSA% value was evaluated using the following formula: CSA% =|CSAcondyle-CSAfossa|÷ CSAcondyle.
Statistical analysis
Statistical analysis was performed using Statistical Package for Natural Science (version 26.0; IBM SPSS; Armonk, New York, USA). The Kolmogorov–Smirnov test was used to verify the normality of all data. Normally distributed data are expressed as mean ± standard deviation (SD) (\(\overline{x} \pm s\)). Non-normally distributed data are presented as quartile (25th percentile, 75th percentile). Pairwise methods were used to perform multiple comparisons. The Kruskal–Wallis H test was performed for the non-normal data. A one-way analysis of variance followed by a least significant difference post hoc analysis was performed for normal data with homoscedasticity. Dunnett’s T3 post hoc test was performed for normal data with heteroscedasticity. P < 0.05 was considered statistically significant. GraphPad Prism software version 6.0 (Graph Pad Software Inc., San Diego, California, USA) was used to plot values. The receiver-operating characteristic (ROC) curve was analyzed to assess the diagnostic efficacy of morphological parameters. By calculating the area under the curve (AUC), the diagnostic accuracy was graded as follows: excellent, 0.9–1.0; good, 0.8–0.9; fair, 0.7–0.8; poor, 0.6–0.7; and failure, 0.5–0.6 [22]. A multivariate logistic ordinal regression analysis was used to investigate factors associated with TMJ ADD. A predictive model was generated based on the results of the multivariate logistic ordinal regression analysis. R software version 4.0.4 (R Foundation for Statistical Computing, Vienna, Austria) was used for mathematical model construction.