30: The temporomandibular joint

The temporomandibular joint

Introduction

The temporomandibular joint (TMJ) is one of the most difficult areas to investigate radiographically. This fact is underlined by the many types of investigations that have been developed over the years. Several plain radiographic projections and various modern imaging modalities are used for showing different parts of the complex joint anatomy. The clinical problems are complicated by the broad spectrum of conditions that can affect the joints, which can present with very similar signs and symptoms, and by prolonged searches for objective signs to explain TMJ pain dysfunction.

From the investigative point of view the knowledge required by clinicians includes:

Normal anatomy

The basic components of the TMJ include:

In addition to this knowledge of the static anatomy, clinicians need to be aware of the types and range of joint movements which result in the condyles moving downwards and forwards when patients open their mouths. These include:

Investigations

Modern imaging of the TMJ is dependent on the facilities available but could include:

Previously described transorbital and transcranial views are now seldom used and are only of historical interest.

Panoramic radiography

Main indications

The main clinical indications include:

Panoramic TMJ programmes

Main indications

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

image
Fig. 30.5 A Patient positioned with the mouth closed within a panoramic unit using the special nose/chin support and B positioned with the mouth open.

• 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.

image
Fig. 30.6 Panoramic TMJ field limitation programme images of normal right and left condylar heads in the mouth closed (c) and open (o) positions.

Transpharyngeal radiography

Main indications

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.

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Fig. 30.7 A Positioning for the left transpharyngeal – the patient is holding the film against the left TMJ, the mouth is open and the X-ray beam is aimed across the pharynx. B The side of the face with various anatomical structures – the zygomatic arch, condyle, sigmoid notch and coronoid process – drawn in to clarify the centring point of the X-ray beam which is marked. C Diagram of the positioning from the front showing the film parallel to the mid-sagittal plane and the X-ray beam aimed across the pharynx. D Diagram of the positioning from above, showing the X-ray beam aimed slightly posteriorly across the pharynx.

Related posts:

  1. 19: Introduction to radiological interpretation
  2. 12: Oblique lateral radiography
  3. 23: Implant assessment
  4. 21: The periapical tissues
  5. 22: The periodontal tissues and periodontal disease
  6. 31: The maxillary antra

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Jan 12, 2015 | Posted by in Oral and Maxillofacial Radiology | Comments Off on 30: The temporomandibular joint

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