Temporomandibular joint (TMJ) ankylosis is a condition in which condylar movement is restricted because of a fibrous or bony union between the mandibular condyle and temporal bone. The soft tissue (fibrous) union of joint components is called fibrous ankylosis, and the interosseous connection of the mandibular condyle to the temporal bone or zygomatic bone is called bony ankylosis [1]. TMJ ankylosis is most often caused by trauma, followed by systemic or local infection, and secondary to unknown causes [2]. Posttraumatic ankylosis occurs predominantly in adults, whereas infection is the most common cause in the pediatric age group [3,4]. TMJ ankylosis has a negative impact on the patient’s mouth opening.

Diagnostic imaging plays a vital role in diagnosing TMJ ankylosis and establishing a treatment plan [5]. Conventional radiography was the common diagnostic imaging technique used before computed tomography (CT) or cone beam computed tomography (CBCT) [6]. However, it was difficult to evaluate the extent of the ankylosing mass through conventional radiography because of poor spatial resolution; there were also limitations in evaluating the need for multiple sections of the joint [7]. CT or CBCT generates image volumes that allow the user to reconstruct a thin cross-sectional image of the anatomy in the coronal and sagittal sections in a modified axis along the long axis of the condylar heads without superimposition of the surrounding anatomic structures. These modified sections provide less distorted representation than conventional radiography.

This report describes a case of a middle-aged woman who developed fibrous ankylosis of the left TMJ while repeating treatment for the mouth opening limitation and pain of TMJ. We report the findings observed via radiographic and CBCT images through continuous observation. The study protocol was approved by the Ethics Committee of Chosun University Dental Hospital (approval no. CUDHIRB 2204 001 Q01), and the need for written informed consent was exempted by the committee.

A 58-year-old female patient first visited our hospital 9 years ago (June 2013) with complaints of teeth mobility, pain, and sound in her jaw while eating. The active mouth opening (AMO) was 28 mm, and there was pain in the right TMJ.

A panoramic radiograph revealed a relatively clear appearance of both mandibular condyles (Fig. 1), along with severely generalized alveolar bone loss. A transcranial radiograph showed that both mandibular condyles were slightly moved in the articular fossa, but they could not move beyond the articular eminence (Fig. 2).

Based on the clinical examination, she was diagnosed with disc displacement without reduction and degenerative osteoarthritis on both TMJs. We recommended medication, physical therapy, and oral appliance treatment, but she did not return to the hospital.

After 3 years (February 2016), she returned to the hospital due to worsening of her mouth opening limitation and pain in the TMJ. The AMO was 20 mm. She had developed these symptoms 4 months earlier and underwent treatment with a stabilized appliance at another clinic for 2 months.

She experienced spontaneous pain that became worse at night, and no change in the symptoms. We administered medication, physical therapy, and oral appliance treatment four times with the same diagnosis, after which she did not visit the hospital again.

After 3 years (November 2019), she returned with the complaint of her mouth opening limitation. Upon clinical examination, the AMO was 25 mm, and there was no pain during mouth opening. A panoramic radiograph revealed a slight deformation in the appearance of both mandibular condyles, and in particular, the cortical bone of the right mandibular condyle appeared irregular (Fig. 3). In addition, there was more severely generalized alveolar bone loss. A transcranial radiograph revealed a slight movement of the mandibular condyle on both sides, which appeared to be lower than previously observed (Fig. 4). In particular, almost no movement was observed in the left mandibular condyle.

On CBCT imaging, the right TMJ showed a very narrow joint space between the mandibular condyle and the articular fossa (Fig. 5A, B), but this joint space was not observed in the left TMJ, and hence appeared to be connected by bone (Fig. 5C, D). The case was diagnosed as bony ankylosis of the left TMJ. Therefore, we performed arthrocentesis twice and prescribed a mouth opening exercise.

The patient returned to the hospital after 2 years (April 2021), and underwent a radiograph. We detected no obvious changes in the mandibular condyle on the panoramic radiograph (Fig. 6). On CBCT, the joint surface of the right TMJ was irregular in the sagittal section (Fig. 7A, B), and the ankylosis of the left TMJ was clearly visible on the medial region (Fig. 7C, D). In the right TMJ, the joint space between the condyle and the fossa appeared slightly wider than that observed previously.

We performed a third arthrocentesis, and the patient stopped visiting the hospital thereafter. On the last panoramic radiograph, the mandibular condyles showed no significant difference compared with the previous radiograph.

TMJ disorders (TMDs) include clinical problems of the masticatory muscles, TMJ, and related structures and are classified as masticatory muscle disorders. TMDs are characterized by pain and dysfunction in the oral and maxillofacial regions. They can be classified into morphological abnormalities, joint disc displacement, dislocation, inflammatory conditions such as synovitis and capsulitis, osteoarthrosis, osteoarthritis, and fibrous and osseous ankylosis [8].

In general, TMJ ankylosis is divided into intra-articular ankylosis and extra-articular ankylosis, and it is further divided into fibrous and osseous ankylosis according to the type of tissue that limits mobility.

As mentioned before, TMJ ankylosis occurs in relation to trauma in most cases and progresses to fibrous or osseous ankylosis along with the arthritis in some cases. The present case, based on the diagnosis of disc displacement without reduction on both TMJ and degenerative arthritis, can be considered a case that progressed to ankylosis over time without proper treatment.

Diagnostic imaging is an essential tool in diagnosing TMJ ankylosis. Previously, conventional radiographs, such as lateral and posteroanterior skull, panoramic, and transcranial radiographs, were primarily used for diagnosing TMJ diseases [9]. As these radiographs overlap anatomical structures, there is a limit to analyzing the structures [10].

CT or CBCT is currently the imaging modality of choice to accurately demonstrate preoperative ankylosing masses and other surgically important findings, such as the outline of the mandibular condyle and pathological changes [6,11]. The osseous changes in the mandibular condyle such as erosion, osteophyte, and sclerosis can be easily identified in the coronal and sagittal sections of CT or CBCT images. In addition, three-dimensional (3D) CT or CBCT and rapid prototyping models provide useful information for radiologists and surgeons in the preoperative period. As these techniques provide an accurate and realistic representation of the joint structure, they are extremely useful for diagnosis and surgical planning [10,12]. In this case, using CBCT, TMJ ankylosis was identified and evaluated in each section.

As mentioned earlier, it is difficult to confirm TMJ ankylosis using conventional radiographs. Therefore, there have been reports of evaluating TMJ ankylosis using CT images, but there no reports of evaluating TMJ ankylosis using CBCT images [7,9-12]. Although the findings of CT or CBCT are not significantly different, CBCT is advantageous because it can evaluate the bone area in more detail with high spatial resolution images and the radiation exposure to the patient is also lower; however, it also has disadvantages because soft tissues cannot be identified. Moreover, when CT or CBCT is used, additional information can be obtained by reconstructing the 3D model. In the present case, the panoramic radiographs and transcranial radiographs did not reveal clear signs of ankylosis. Several cross sections were observed on CBCT to confirm ankylosis.

When the patient first visited the hospital, we believed that her condition could have been diagnosed quickly if it had been immediately confirmed with CBCT and magnetic resonance imaging to identify the cause of the mouth opening limitation. Unfortunately, there were several difficulties until the final diagnosis because the patient did not visit the hospital regularly.

In conclusion, the patient did not receive appropriate treatment for TMJ arthritis and visited the hospital repeatedly only when symptoms were present, resulting in ankylosis. However, conventional radiographic examination could not accurately evaluate the changes in the mandibular condyle, whereas CBCT could detect ankylosis. Therefore, dentists and oral and maxillofacial radiologists should approach the diagnosis and treatment of TMDs with more caution.

No potential conflict of interest relevant to this article was reported.