I Can See Clearly Now

By Paul Feuerstein, DMD

I recently saw a long-standing patient, about 40 years old, with no restorations in his mouth, who complained about sensitivity on a lower cuspid.

A clinical exam found a large defect on the lingual going a few millimeters below the gingival margin. A PA showed a circular radiolucency in the middle of the root at the CEJ level. Since the lesion was palpable from the lingual, it was not clear if this was an exposure due to superimposition in the image.

I sent him to a local endodontist who had just received a cone beam unit. Using a very small field of view, I was sent a disk with the tooth scan viewable in a 360-degree 3D rotation. The lesion was now shown to be an obvious exposure, but the damage was much more extensive than I had imagined.

Any thoughts of a simple lingual perio exposure and restoration were out of the question. This was some sort of resorption. The patient was informed that in his (up-until-then) perfect mouth, he was about to have an extraction and probable implant.

In the past couple of years, more endodontists are purchasing cone beam units and using them on a daily basis. Since they have been in the forefront of using microscopes to be more accurate, this should be no surprise given the meticulous tiny area of endodontic treatment.

Last summer the American Association of Endodontists (www.aae.org/colleagues) published an article by Dr. Frederic Barnett about cone beam computed tomography (CBCT) in endodontics. (The website also has three additional articles related to this topic.)

By way of introduction, “CBCT for endodontic purposes appears to be the most promising use of CBCT, in many instances instead of 2-D images. Applications would include apical lesions, root fractures, canal identification, and characterization of internal and external root resorption.”

The original CBCT units were “full volume,” showing both arches, the TMJ, and surrounding areas, larger than the traditional panoramic.

“Zooming in” on a single tooth was possible. But the time, and of course radiation, as well as the cost of the larger sensor plates in the machines made this impractical. A new generation of units allows the practitioner to define which area needs to be inspected.

These have a smaller field of view and allow the operator to capture an area as small as a quadrant. This lowers the radiation and increases the resolution. The cost of these units is slightly lower, partially due to the smaller sensor.

Dr. Barnett points out that these new units improve the diagnostic accuracy of endodontic-specific tasks such as the visualization of small features. This includes calcified/accessory canals, missed canals, etc.

There are several cases in which patients have had symptoms, but the traditional 2-D radiograph appears normal. In one case shown, until the apical area of the root canal is viewed mesial to distal instead of buccal-lingual, the lesion is not evident. In another, an axial slice shows a clear fracture that is not evident in traditional review.

Canals can be seen more clearly. In a situation in which treatment failed in a lower second premolar, which typically has one canal, the mesial-distal view clearly showed a buccal canal unfilled. This is a perspective similar to one bowling pin in front of another.

Other examples of the benefits of these scans are situations where a tooth has been traumatized and appears okay on standard imaging. A 3-D view can show a luxation and fracture of the labial plate. Just seeing a few of these cases makes you sit back and wonder what else we are missing in this traditional 2-D world.

Of course, CBCT can also be used preoperatively to see root morphology, including the infamous MB2 canal. Dr. Barnett cautions, though, that CBCT is not to be used routinely at this point, especially in the absence of any clinical signs and symptoms. But I must assume this is related to the concern about additional radiation (although minimal in the limited-field CBCT) and perhaps cost constraints.

An interesting point he makes refers to the limited field vs. full volume as a smaller area of responsibility. This point is important as stated by the AAE: “Clinicians … are responsible for interpreting the entire image volume … Any radiograph may demonstrate findings that are significant to the health of the patient. There is no informed consent process that allows the clinician to interpret only a specific area of an image volume. Therefore, the clinician can be liable for a missed diagnosis, even if it is outside his or her area of practice. Any questions by the practitioner regarding image data interpretation should promptly be referred to a specialist in oral and maxillofacial radiology.”

Think about all of this the next time you place a file into a canal.

Dr. Paul Feuerstein installed one of dentistry’s first computers in 1978. For more than 20 years, he has taught technology courses. A general practitioner in North Billerica, Mass., since 1973, Dr. Feuerstein maintains a website (www.computersindentistry.com), and can be reached at [email protected].