Imaging findings
Case 316
【Progress】
She was scheduled to take oral rehabilitation and brace.
【Discussion】
Mastication initiates from taking food at mouth entrance. Opening and closing mouth is preserved by innervation of mandibular branch of trigeminal nerve. Trigeminal nerve includes three branches: ophthalmic, maxillary and mandibular branch nerves. The ophthalmic and maxillary nerves purely sensory innervation and the mandibular nerve has sensory and motor functions (1, 2).
Lateral pterygoid muscle works to open mouth, while medial pterygoid muscle works to close mouth. Both muscles get blood supply from superficial temporal branch artery. They connect articular disk in an articular capsule of the jaw joint (1,2).
Articular disk is required to reduce friction between mandibular fossa of temporal bone and condylar process (head) of mandibular bone (3-5). Virtually, osteosclerosis, deformity or destruction of the condylar head would occur without articular disk because condylar head would directly hit to anterior tubercle without articular disk. Articular disk, configured like a necktie, rides on condylar head in opening and closing mouth.
In closing mouth in normal situation, articular disk rides on condylar head a little anteriorly, while in opening mouth, articular disk just fit to ride condylar head at center. Dislocation of articular disk tends to shift more anteriorly in closing mouth. It is mildly anterior dislocation returns to make fit in opening mouth, that indicates dislocation with reduction. Meanwhile, dislocation anteriorly not only in closing mouth but also in opening mouth that indicates dislocation without reduction. Dislocation without reduction implies more stage-advanced than dislocation with reduction (6 – 8). Dislocation without reduction also associates with flattening or deformity of condylar head (7, 8). Although the reason remains unclear, articular disk dislocation predominantly occurs in middle-aged female rather than male (1, 2).
In our case of a forty-two-year-old female, MRIT2WI sagittal images of right jaw joint depict anteriorly dispositioned articular disk in both closing mouth and opening mouth, indicating dislocation without reduction, while those of left jaw joint, anteriorly dispositioned disk in closing mouth but returned to original fitting position in opening mouth, indicating dislocation with reduction. Further, right articular disk is shrunken with deformity of condylar head, indicating chronic, time-passed process right jaw joint osteoarthritis. Then, it is crucial to check not only to check displacement of articular disk with or without reduction but also to check configuration of condylar head.
【Summary】
We presented a forty-two-year-old female for more painful right jaw joint rather than left jaw joint. MRT2WI images depict right articular disk displaced anteriorly in both closing and opening mouth, indicating dislocation without reduction, while those depict left articular disk displaced anteriorly in closing mouth and returned to original position in opening mouth, indicating dislocation with reduction. It is borne in mind that normal position of articular disk (necktie configuration) places slightly anterior to condylar head and fit to ride on condylar head in opening mouth. Articular disk tends to displace anteriorly and in case of displace anteriorly without reduction, it associates with deformity and/or shrinkage of condylar head. In radiological interpretation, it is crucial to check not only to check displacement of articular disk with or without reduction but also to check configuration of condylar head.
【References】
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2023.11.14