Mimics medical 21

DICOM of the MRI in the closed mouth position were used for threshold segmentation (Greyscale Value: 0–235) using Mimics Medical 21.0 software (Materialise, Belgium). Owing to the similar density between TMJ disc, the bone cortex of the condyle, articular eminence and the fossa, an experienced assessor would revise the segmentation manually in order to amend the disc border. After isolating the disc mask from the image background, the masks of discs were acquired to create 3D models of the discs (Fig. 1; Additional file 3).Fig. 1

The workflow of the 3D reconstruction of the TMJ disc

The overall disc volume and dimension of superficial area of the 3D disc model were then calculated. Disc length was measured as the maximum length along the sagittal plane, while the width was measured as maximum length along coronal plane. Furthermore, the maximum cross-sectional area in coronal plane and maximum longitudinal-sectional area in sagittal plane was measured. The condylar height was defined as the vertical distance between lines N and N′ as previously described [17 (link)]. The tangent of the posterior margin of mandibular ramus and the condyle was defined by Line R. Line N was a vertical line of the line R and tangent to the lowest point of the mandibular sigmoid notch. Line N' was designated as a parallel to line N and tangent to the condylar head (Additional file 4).

Patient’s CT scan data were input with Digital Imaging and Communications in Medicine (DICOM) format (Siemens CT machine, SOMATOM Sensation 16, Siemens AG, Forchheim Germany), the thickness of the fault was 2 mm so as to make a suitable virtual whole spine. All the tomographic pictures of the patient were imported into Mimics Medical 21.0 (Materialise NV, Leuven, Belgium). Virtual 3D model was created for measurements and 3D printing with threshold of 226-3071HU.