The main clinical indications include:

Technique summary

Conventional panoramics usually image both condylar heads, although to guarantee this the technique can be modified by raising the X-ray tubehead and cassette carriage assembly to a slightly higher level in relation to the patient (so-called high panoramic, as shown in Fig. 30.4).

The main clinical indications are the same as for a conventional panoramic radiograph. If the equipment includes specific TMJ programmes these should be regarded as the views of choice as additional information can be provided when the mouth is opened.

Technique summary

The technique can be summarized as follows:

• The patient is positioned with their Frankfurt plane angled 5° downwards within a panoramic unit with their mouth closed but using a special nose/chin support as shown in Fig. 30.5A instead of the bite-peg

• The head is accurately positioned using the light beam markers and immobilized using the temple supports

• The distance from the external auditory meatus to the canine light is measured and the anteroposterior position of the chin support adjusted manually to ensure that the condyles appear in the middle of the image

• During the exposure, first the left and then the right condyle is imaged in the closed position

• The equipment automatically returns to the start position

• The patient is instructed to open the mouth, as shown in Fig. 30.5B

• The left and right condyles are then exposed in the open position and the resultant image is shown in Fig. 30.6.

The main clinical indications include:

Technique and positioning

This projection can be taken with a dental X-ray set and an extraoral cassette. The technique can be summarized as follows:

1. The patient holds the cassette against the side of the face over the TMJ of interest. The film and the mid-sagittal plane of the head are parallel. The patient’s mouth is open and a bite-block is inserted for stability.

2. The X-ray tubehead is positioned in front of the opposite condyle and beneath the zygomatic arch. It is aimed through the sigmoid notch, slightly posteriorly, across the pharynx at the condyle under investigation, as shown in Fig. 30.7. Usually this view is taken of both condyles to allow comparison.

Diagnostic information

The information provided includes:

• The shape of the head of the condyle and the condition of the articular surface from the lateral aspect (Fig. 30.8)

• A comparison of both condylar heads.

Cone beam CT

Cone beam CT (CBCT) described in Chapter 16 is increasingly being used as an alternative to CT to image the bony elements of the TMJ as shown in Figs 30.9 and 30.10. Sectional or slice images of all aspects of the joints are produced, but in addition, using appropriate software, 3-D images can be created, as shown in Fig. 30.11.

Magnetic resonance (MR)

Magnetic resonance imaging described in Chapter 18 is now established as one of the more useful investigations of the bony and soft tissue elements of the TMJ. It is particularly useful for determining the position and form of the disc when the mouth is both open and closed (see Fig. 30.12). As mentioned in Chapter 18, cineloop or pseudodynamic echo sequences are generally used for TMJ imaging:

Computed tomography (CT)

Computed tomography described in Chapter 18, like cone beam CT, provides sectional or slice images of the joint. The advantages of CT are that it can produce images of the hard and soft tissues in the joint, including the disc, in different planes.

These include:

Technique (Fig. 30.13)

This can be summarized as follows:

1. Non-ionic aqueous contrast medium (e.g. iopamidol-Niopam® 370) is injected carefully into the lower joint space, using fluoroscopy to aid the accurate positioning of the needle.

2. The primary record is obtained ideally using video-recorded fluorography or cinefluorography which allows imaging of the joint components as they move. Only the lateral aspects of the joints are seen.

3. Thin-section tomography of the joint can also be performed if required, to provide information on the medial and lateral aspects of the joint. Typically, five or six slices, 2–3 mm apart, are used with the patient’s mouth open and closed.

4. If further information is required, the contrast medium can be introduced into the upper joint space and the investigation repeated.

Arthroscopy

Arthroscopy gives direct visualization of the TMJ and allows certain interventional procedures to be performed; these include:

Arthroscopy is usually considered as the last line of investigation before full surgical exploration of the joint is carried out.

TMJ (myofascial) pain dysfunction syndrome

This is the most common clinical diagnosis applied to patients with pain in the muscles of mastication, often worst in the early morning and evening, with occasional clicking and stiffness. The aetiology is said to include anxiety or depression, malocclusion, or muscle spasm.

Internal derangements

Symptoms include clicking, which may be painful, pain from the joint and/or musculature, trismus and hesitation of movement and locking usually with failure of opening. Conventional radiography may have revealed an alteration in the position of the head of the condyle, implying an abnormality in disc position. MRI is the investigation of choice to show:

Osteoarthritis

This degenerative arthrosis increases in incidence with age and commonly causes pain in the stressbearing joints, such as the hips and spine. It is now thought to be a systemic disease, or a complication of internal derangement of a joint, and stress merely causes the affected joint to be painful. Radiographic signs of osteoarthritis of the TMJ are often seen in the elderly, but are frequently of no clinical significance. Symptoms, if they occur, can include painful crepitus and trismus and are usually persistent.

Main radiographic features (see Figs 30.14–30.17)

These include:

• Osteophyte (bony spur) formation on the anterior aspect of the articular surface of the condylar head. The radiological appearance of small osteophyte formation is often referred to as lipping; extensive osteophyte formation is referred to as beaking

• Flattening of the head of the condyle on the anterosuperior margin

• Subchondral sclerosis of the condylar head which becomes dense and more radiopaque – a process sometimes referred to as eburnation

• A normal outline to the glenoid fossa though it may also become sclerotic

• Very rarely, there may be evidence of:

– Osteophyte formation posteriorly

– Subchondral cysts

– Erosion of the articular surface of the condylar head.

Rheumatoid arthritis

Rheumatoid arthritis is a generalized, chronic inflammatory, connective tissue disease affecting many joints. TMJ involvement can be found, particularly in severe rheumatoid arthritis, but even then TMJ symptoms are usually minor.

Main radiographic features (see Figs 30.18–30.20)

These include:

• Flattening of the head of the condyle

• Erosion and destruction of the articular surface of the head of the condyle which may be extensive causing the outline to become irregular

• Occasional osteophyte formation on the condylar head

• Hollowing of the glenoid fossa

• Reduction in the range of movement

• Features are usually bilateral and fairly symmetrical.

Juvenile rheumatoid arthritis (Still’s disease)

The radiographic features of juvenile rheumatoid arthritis are similar to the adult disease. In severe cases, the disease may cause interference with normal condylar growth producing micrognathia, or it may result in TMJ ankylosis.

Ankylosis

True ankylosis, i.e. fusion of the bony elements of the joint (see Fig. 30.21), is uncommon but is usually the result of:

Tomography, cone beam CT or CT are the investigations of choice because of the obvious problems of opening the mouth.

Tumours

Benign or malignant tumours develop occasionally in the head of the condyle. The radiographic features depend on the type and nature of the tumour involved, but there is usually an alteration in the shape of the condylar head. Typical examples include osteoma, chondroma (see Fig. 30.22) and chondrosarcoma.

Fractures and trauma

Fractures of the condylar necks are common after a blow to the chin (see Ch. 29). Very occasionally with this type of injury the condylar neck does not fracture but the head of the condyle either fractures, a so-called intra-capsular fracture (see Fig. 30.23) or is forced upwards, through the glenoid fossa into the middle cranial fossa (see (Fig. 30.24). Tomography, cone beam CT or CT will demonstrate the extent of any injury. Trauma can also result in unilateral or bilateral dislocation (see Fig. 30.25).

Developmental anomalies

Developmental defects affecting the TMJ are usually investigated using conventional radiography. They can be divided into:

• Condylar hypoplasia (unilateral or bilateral) (see Fig. 30.26)

• Condylar hyperplasia (unilateral or bilateral) (see Fig. 30.27)

• Bifid condyle (see Fig. 24.30)

• Post-radiotherapy

• Defects associated with specific disease or syndromes, for example:

– First arch syndrome

– Mandibular facial dysostosis (Treacher Collins syndrome).