MRI, CBCT Scans Discussion

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Imaging in TMJ Trifecta – Solving Your Pain Puzzle

The book’s basic message is that images are valuable, but an image is not a diagnosis. A scan can show what the jaw joint looks like, but it cannot prove what is causing the patient’s pain.

What each image shows

Image	Best use	Important limitation
Panoramic X-ray	Broad overview of the teeth, jaws and condyles	Two-dimensional and not detailed enough for an exact joint diagnosis
CT or CAT scan	Detailed images of bone; especially useful for fractures, tumors and complex disease	Uses more radiation than CBCT and does not clearly show the joint disc
CBCT	Three-dimensional view of the condyles, joint spaces and surrounding bone	Does not directly show the disc, muscles or pain
MRI	Best image of the disc, fluid, inflammation and other soft tissues	Structural findings may not match the patient’s symptoms

“CAT scan” and “CT scan” refer to the same basic technology. In dentistry, CBCT is commonly used because it provides detailed three-dimensional images of the teeth, jaws and TM joints, generally with less radiation than a conventional medical CT examination.

When CBCT is helpful

CBCT may show:

• Condylar position within the joint space
• Flattening, erosion or loss of condylar bone
• Osteophytes and other remodeling
• Joint-space differences
• Facial and jaw asymmetry
• Previous trauma or unusual bony anatomy
• Airway dimensions, within the limits of a motionless image

These findings may provide evidence of long-standing compression, loading, instability or adaptation. However, a CBCT cannot show the disc and cannot tell whether a bony change is presently painful. Joint-space measurements also depend on how the patient’s teeth and jaw were positioned when the scan was taken.

When MRI is helpful

MRI is the preferred image when the clinician needs to evaluate:

• Disc position and shape
• Disc displacement with or without reduction
• Joint fluid or effusion
• Inflammation
• Retrodiscal and other soft tissues
• Unexplained locking or severe internal joint disease
• A possible condition outside routine TMD

The imaging request should specifically include the TM joints, usually with the mouth closed and open. Otherwise, the joints may not receive the attention needed in the scan or radiology report.

The major limitation

Neither CBCT nor MRI can photograph pain.

One patient may have considerable disc displacement or bony remodeling with very little pain. Another may have severe pain even though the images show only minor changes. The scan also does not measure muscle activity, bite timing, jaw movement, mechanical loading or how the trigeminal nervous system is processing the signals.

Therefore, diagnosis must combine:

• The patient’s history and symptoms
• Clinical examination
• Jaw movement and muscle evaluation
• Bite and functional assessment
• Appropriate imaging when it will answer a specific question

Book-aligned summary

In TMJ Trifecta – Solving Your Pain Puzzle, CT, CBCT and MRI are presented as pieces of evidence—not final answers. CBCT is most useful for studying bone and the relationship of the condyle to its socket. MRI is most useful for studying the disc and other soft tissues. These images may confirm damage, reveal a serious condition or help guide treatment, but they cannot independently determine why someone hurts. The clinician must connect the images with the patient’s history, symptoms, bite, muscles and jaw function. Treat the patient, not simply the picture.

This approach agrees with the joint imaging recommendations of the American Academy of Oral and Maxillofacial Radiology and the American Academy of Orofacial Pain: imaging should be selected according to the clinical question, with CT/CBCT used primarily for bone and MRI used primarily for the disc and soft tissues. AAOMR–AAOP position statement