Case of the Month

An intriguing dental scan and how to interpret it

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Internal Derangements of the Temporomandibular Joint (TMJ)

Rx Scanner: MYRAY Hyperion X9 Pro


EFFECTIVE DOSE: 7 mA x 80.0 Kv

CLINICAL PARTICULARS: Bilateral TMJ (Temporomandibular Joint) Rx Scan in both Open-Mouth and Closed-Mouth positions to examine a Patient experiencing pain when opening their mouth fully and chewing. Resistant to long-term pain-relieving therapy.

Case of the month


The radio morphology of the condyles, cortical thickness, and structure appears normal. The cortical thickness of the corresponding glenoid fossa and the anterior and posterior prominences height look normal. No radiopathological evidence is visible in the mastoid region.

In the open position, the condyles slide over the articular prominence (reversible snap?).

Articular disc and pterygoid muscle pathologies are evident in the dynamic MRI of the TMJ.


The temporomandibular joint is a double condylar diarthrosis that consists of two articular surfaces, an intra-articular disc, a capsule, and ligaments. It is referred to as double due to a complex capsular, disc, and synovial structure that divides the joint cavity into two functional and anatomical parts.

The articular surfaces comprise the mandibular condyle surface, the temporal tubercle, and the glenoid cavity. The two articular surfaces are connected through the interposition of an oval-shaped articular meniscus that provides continuity with the joint capsule. The lateral and medial parts of the fibrocartilaginous disc are inserted into the condyle via the disc’s lateral ligaments. In the meniscus, two well-defined zones are anatomically and macroscopically noticeable, which, continuing anteroposteriorly, are comprised of the articular disc and the bilaminar zone.

  • Bilaminar zone: the bilaminar zone is called this way because it comprises two fasciae, an upper and a lower one, made of fibrous tissue between which lies a retrodiscal pad. Since the bilaminar zone is a whole with the other zones of the meniscus, it follows the latter in meniscal movements: thereby filling the space that would otherwise be left empty by the condyle during the translation movement, thus creating a negative pressure that becomes positive again when the condyle returns to its place.

Bilaminar zone
From a functional standpoint, the TMJ is divided into two parts; condylar-discal and temporo-discal. The condylar-discal part is involved in the rotational movement, which constitutes the first phase of mouth opening, while the temporodiscal part contributes to the downward and forward displacement of the condyle head by continuing the rotation of the first phase. The synergy of the two phases thus creates a complex roto-translational movement, resulting in the opening of the mouth.


The clinical symptoms of temporomandibular dysfunction, more commonly referred to as temporomandibular disorders (TMD), can be differentiated into:

  • Condylar-discal incoordination: Condylar-discal incoordination is characterized by a disruption of the synergy of the articular disc concerning the mandibular condyle. There can be four main clinical scenarios depending on the evolution and affect of the articular structures:
  1. Anterior TMJ dislocation
  2. Reducible joint disc dislocation (joint click)
  3. Irreducible joint disc dislocation (closed lock)
  4. Secondary osteoarthritis.
  • Muscular disorders: masticatory muscle disorders are those related to altered muscle tone, and the main clinical pictures consist of:
  1. Muscle splinting (protective co-contraction)
  2. Non-phlogistic myalgia (local muscle soreness)
  3. Myofascial pain
  4. Myositis and Myospasms


Internal derangements may develop if the disc morphology is altered and the disc ligaments are elongated. The dislocation’s extent depends on the disc’s severity and ligament alterations. If the articular disc remains in a forward position relative to the condyle, the dislocation is defined as “without reduction”. A reduced mouth opening (locked jaw) and pain in the ear and the temporomandibular joint area may arise. If, at some point in the joint’s range of motion, the disc returns to the head of the condyle, this is referred to as dislocation “with reduction”. Painless dislocation with reduction occurs in approximately one-third of the population at some point.

All types of dislocations can lead to capsulitis (or synovitis), which is the inflammation of the tissues surrounding the joint (e.g., tendons, ligaments, connective tissue, synovium). Capsulitis may also develop spontaneously or originate from arthritis, trauma, or infection.


A disc dislocation with reduction often involves a painless clicking or popping when opening the mouth. Pain may also be felt, particularly when chewing hard food. Patients are often embarrassed because they think others can hear the clicking noise when they chew.

Disc dislocation without reduction usually involves no sound; however, the maximum mouth opening between the upper and lower incisors is limited. This usually involves pain and changes in patients’ perception of their occlusion. It usually appears severely in patients suffering from chronic articular clicking; around 8-9% of the time, the patient wakes up unable to open their jaw fully.

In a small percentage of patients, the symptoms of disc dislocation without reduction self-heal spontaneously after 6-12 months.

Capsulitis causes localized joint pain, soreness, and sometimes a reduction in jaw opening.


A temporomandibular joint X-ray (and TMJ CBCT, indicated in case of patients with an already ascertained pathology) is a radiological examination used to determine any abnormalities that may affect the temporomandibular joint (TMJ).

No prior preparation is required to perform the temporomandibular joint X-ray, nor is it necessary to suspend medication. It is a quick, painless, and non-invasive examination that takes about 15 minutes.

If wearing them, the patient must take off any metal objects such as jewelry and dental prosthesis and wear a protective device to shield themselves from radiation.

The examination is performed with the patient standing with their head resting on a special support placed in front of the machine that emits the photon beam and records images. To ensure correct imaging, the patient must remain as still as possible and hold their breath when prompted by the operator.

During the examination, two projections are performed, both with open and closed mouth, allowing the different positions of the anatomical part during chewing to be observed.

For more detailed diagnostics regarding the TMJ examination, patients are referred to Functional Magnetic Resonance Imaging (MRI).

Functional MRI diagnostic objectives:

  • Morphological examination
  • Evaluation of spatial relationships between condyle, disc, fossa
  • Evaluation: Static, Pseudo-dynamic, Dynamic

Written by Dr. Lucisano Francesco Lead Radiographer – DentQ Italy

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