TMJ radiographic techniques

:Techniques 1 -plain radiography

2- panoramic radiography3- Tomography4- Arthrography5- Computed tomography (CT)6- Magnetic resonance imaging (MRI)

*Plain radiography :

Plain films of TMJ are made with a stationary x-ray source and film. In order to avoid superimposition of adjacent anatomic bony structures making visualization of all parts of TMJ, different projections of transcranial films :have been applied, which include

- lateral transcranial view - transmaxillary view

- submental-vertex view - transpharyngeal view

-lateral transcranial

-Transmaxillary

-Submental vertex

-Transpharyngeal view

*Panoramic radiography

It’s a good imaging method for evaluating TMJ since information about the teeth and other parts of the jaws were also shown on the image

However, the relationship between the condyle and glenoid fossa cannot be evaluated in the panoramic film because the fossa cannot be seen with superimposition of the base of the skull and zygomatic arch.

The morphology of the condyle becomes wider than the anatomic structure of the condyle

*Tomography

Tomography of TMJ is generated through the synchronous movement of the x-ray tube and film cassette through an imaginary fulcrum located in the center of the desired imaging plane. Linear tomography and complex tomography are involved

tomography is a good method for depicting the osseous changes with arthrosis in TMJ

For evaluation of condyle position in glenoid fossa of TMJ, tomography has been reported to be more reliable than plain film and panoramic radiography

On the other hand, the relationship between the condyle position and disc displacement is uncertain. The condyle position is not reliable in estimating the disc displacement of TMJ and related symptoms

The major disadvantage of tomography is the lack of visualization of the soft tissue of TMJ, a problem shared with plain film radiography.

*Arthrography: A 25 or 23 gauge needle is placed into the inferior joint space immediately posterior to the condyle. Small amounts of iodinated contrast are injected under fluoroscopy. The contrast tracks along the posterior, superior and anterior portions of the condyle. The anterior collection of contrast, called the anterior recess, normally has a smooth, tear-drop shape .

If the meniscus is perforated, contrast flows into both the superior and inferior joint recesses. However, the arthrographic needle can inadvertently puncture the meniscus and cause iatrogenic filling of both joint spaces.

*computed tomography (CT):Computed tomography (CT) can be used to diagnose internal derangement and other disorders of the TMJ.

The patient is scanned in either the transverse or direct sagittal plane using thin sections (1-2 mm) and a soft tissue technique.

If transverse sections are obtained, sagittal reconstructions are made through the condyle.

The meniscus can be visualized on CT since it is slightly higher in density than the surrounding muscle and soft tissue.

Normally, there is only a small amount of increased soft tissue density anterior to the condyle on CT. In internal derangement, the anteriorly displaced meniscus results in abnormally increased soft tissue density anterior to the condyle.

*Magnetic resonance imaging (MRI)Magnetic resonance (MR) can also be used to diagnose internal derangement and other disorders of the TMJ.

The patient is scanned in the sagittal plane using a surface coil and a high resolution technique

The low intensity cortex of the condyle surrounds the high signal fat in the marrow. The meniscus is a low intensity structure which is attached posteriorly by the intermediate intensity bilaminar zone.

Normally, the anterior band lies immediately in front of the condyle. The junction of the bilaminar zone and the meniscus normally lies at the superior aspect of the condyle.

In internal derangement, the meniscus is abnormally positioned anterior to the condyle.