PMC7333388_01
Images of the teeth and radiographic and computed tomographic images of the temporomandibular joint (TMJ). a The labial portion of the canine tooth (red ellipse line) in the left maxilla is worn down by the opposite portion in the left mandible. b The jaw is maximally opened, but locking occurs between the left canine teeth. c After crown reduction of the canine teeth was performed, the jaw could be opened to a greater extent than shown in (b). However, normal mouth opening was not performed (maximum 2 cm). d The left TMJ shows a more prominent irregular joint surface than does the right TMJ on the anterior-posterior view. e & f The joint space widening and joint surface irregularity are more severe in the left TMJ than in the right TMJ on the left and right oblique views. The blue ellipse lines indicate the left and right TMJs. g The joint space widening and joint surface irregularity are more severe in the left TMJ than in the right TMJ. h TMJ image of a normal rhesus monkey
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Fig1
After quarantine, lockjaw was identified (Fig. 1b and supplementary video 1). Moderate to severe attrition was identified in the middle labial portion of the left maxillary canine, which was caused by the locked portion of the left mandibular canine (Fig. 1a). More severe irregularity in the joint surface was observed in the left TMJ compared with the right TMJ in the radiographic and computed tomographic examinations (Fig. 1d-h), and the diagnosis based on these examinations was DJD of both TMJs with fibrous ankylosis.  The mouth opening distance slightly increased, and the maximum distance of mouth opening was approximately 20 mm after the locked portion of the left canine teeth was removed (Fig. 1c and supplementary videos 3 and 4).
Gross images of the TMJ and microscopic images of the articular surface of the TMJ of the right mandible taken during necropsy. a & b Degenerated cartilage and adhesive fibrotic tissue are identified in both TMJs (a; mandible, b; temporal bone). c and f The articular cartilage of the TMJ is replaced by fibrotic tissue in the scan view. d and g Magnified image of the right square in (c) and (f). Fibrocartilage in most areas of the TMJ is identified, and normal cartilage is absent. This fibrocartilage is more cellular than normal articular cartilage, and the unevenly distributed collagen arrays are disorganized. There is no inflammatory reaction. e and h Magnified image of the left square in (c) and (f). Proliferative bland-looking fibroblasts are located in marrow tissue and adjacent bony tissue. c, d, and e; h & e staining. f, g, and h Masson's trichrome staining. Bar = 50 mum
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Fig2
The masseter muscle appeared normal, and fibrotic synovial tissue and joint surface irregularity were observed by necropsy (Fig. 2a&b). The presence of fibrocartilage in most areas of the TMJ was confirmed by histology (Fig. 2c-h). The diagnosis was fibrous ankylosis of the TMJ associated with DJD.