7 Imaging-Based Diagnostic Tests for TMJ Disorders

1. Jaw Bone Scan with Radionucleotide

Bone scans are utilized to assess bone tissue growth. It is an older technology and less specific technology (2D) than SPECT (3D), but it still has a role in diagnosis of bone scan. After the injection of the nucleotide, a gamma camera is used to capture the radiation emitted by the radiotracer (nucleotide) and generates a representative two-dimensional image of the uptake. This method is used to determine if a TMJ lesion, such as osteochondroma, is still actively growing.

Evidence Needed to Order a Jaw Bone Scan

  1. Progressive abnormal growth of the jaw or condyle (hyperplasia, hypertrophy, or osteochondroma)
  2. Clinical examination of the teeth indicating the growth may have stopped

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2. Head or Neck Imaging with SPECT or PET/CT

Positron emission tomography (PET) scanning and single photon emission computed tomography (SPECT) are both utilized to assess bone tissue growth by using radioactive atoms or molecules that emit gamma rays. SPECT does not reliably differentiate between a benign slow growing osteochondroma and a faster growing early phase chondrosarcoma.

When combined with CT, PET/CT imaging allows early detection of growth and more precise localization of the problem. PET/CT is used exclusively for tumor assessment. Because glucose is metabolized differently by benign versus malignant tumors, the PET scan can distinguish them. The accuracy of PET imaging increases when combined with a CT (PET/CT). Unfortunately, there are false positives in benign lesions with high bone activity (osteomyelitis, fibrous dysplasia, osteoblastoma, Paget’s disease, and aneurismal bone cyst).

Clinical history or examination evidence needed to order a SPECT or PET/CT test includes lesion of the bone that appears to be growing.

3. Beighton Hypermobility Score

The Beighton score is used to assess for joint laxity and hypermobility. It uses a simple 9-point system, where the higher the score the higher the laxity. The threshold for joint laxity in a young adult is ranges from 4-6. Thus a score above 6 indicates hypermobility, but not necessarily true. Evidence needed to order this test includes thin tall young female with clicking or locking of the jaw.

4. Surface Electromyography

Surface electromyography is a method to document the presence and magnitude of muscle activity. Unfortunately, there is about a 15-20% error in the signal level every time the surface electrodes are attached, removed, and reattached. This data suggests that the test-retest variability of surface EMG method is not negligible and might account for as much as one-fifth to one-third of the measured level. For this reason, a consistent link between a muscle pain state and surface EMG resting jaw muscle tone level is not established.

To have diagnostic value, a test must be nearly always positive in the patient and almost never positive in the control. Surface electromyography does not satisfy this requirement and is difficult to find diagnostic value in this methodology. At best, this method can be no more than an ancillary device that is documentary. The utility of surface EMG recordings must be judged as of low to no value.

This method of diagnosis is not reliable or specific enough to justify its use in orofacial pain or temporomandibular disorders.

5. Bite Force and Tooth Contact Measurement Sensors

There is a device that can detect and and display the occlusal contact information gathered by the pressure sensitive film inserted between the teeth instantly on a monitor. The question of importance is “Can the pressure sensitive film reliably identify natural multiple contacts on teeth?” To date, the accuracy of these devices have been significantly limited. The pressure sensitive film is too thick and results in heavier contacts on the posterior teeth than the anterior teeth.

These devices might have documentary value of the occlusal contact patterns on the teeth, but artifacts will likely be a problem until a thinner recording paper is developed. Until such time, these instruments will have limited utility.

This method of diagnosis is not reliable or specific enough to justify its use in orofacial pain or temporomandibular disorders.

Related Reading: Dentist’s Guide to Tooth Erosion, Attrition, Abrasion & Abfraction

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6. Computerized Jaw Tracking

Jaw-tracking devices’ diagnostic value for detecting TMD are not well supported by any scientific evidence. In patients with trismus or a true intracapsular disk dysfunction, the jaw range of active motion is reduced from normal. However, there is significant overlap with healthy normals who have limited opening.

The current standard approach to monitoring jaw opening and lateral movement ability uses a millimeter ruler. This technique is highly reproducible within and between investigators.

The millimeter ruler method cannot be used to assess dynamic movement irregularities, such as abnormal but non-restricted movements. Extensive descriptive normative data on jaw movement has been gathered on patients and healthy study populations, but no mandibular movement patterns are valuable as a diagnostic test to reliably differentiate a temporomandibular disorder patient from a non-patient that cannot be seen with the naked eye.

This method of diagnosis is not reliable or specific enough to justify its use in orofacial pain or temporomandibular disorders.

7. Joint Vibration Signals

Claims for the use of sonography and vibratography machines to discriminate between various intracapsular TMJ conditions have not been substantiated by well-designed research. Until acceptable levels of technical and diagnostic validity have been clearly established, these diagnostic devices cannot be relied on as aids in differential diagnosis or in clinical decision in TMD.

Researchers have attempted to objectively measure joint sounds with vibration or sound sensors and link this sound to specific temporomandibular joint dysfunctional conditions. Digital sound data was even submitted to a frequency analysis to better quantify the various types of TM joint sounds. The reproducibility of consecutive joint sound measurements was reported to be relatively high.

A major problem with interpreting any joint sound data is the high prevalence of temporomandibular joint sounds in otherwise asymptomatic individuals. Reports state 25-50% of the normal joints produce occasional sounds at opening or closing. If a high sensitive device is used to detect the joint sounds, it is very likely that normally undetectable sound emanating from an asymptomatic joint might be mistaken as pathology, raising the possibility of false positives.

Currently, the clinical value of TM joint sound recording is questionable and considering these facts, it can be said the utility of joint sound recordings must be considered low.

Additional Articles on Treating TMJ Disorders

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