Removal of impacted mandibular third molars is certainly the leading dental cause of injury to the inferior alveolar nerve.1 Assessment of the relationship between the third molar and the nerve assists the dentist or surgeon in deciding whether or not to remove the tooth electively, or in planning the surgical approach, when the indication for removal is established (infection, cyst, tumor, periodontal condition of adjacent tooth, etc.).
Dr. Luigi Checchi and colleagues, in their March JADA article, "Reliability of Panoramic Radiography in Evaluating the Topographic Relationship Between the Mandibular Canal and Impacted Third Molars," want to establish the computed tomographic, or CT, scan as the standard of care for evaluating the third molar/mandibular canal relationship in patients whose panoramic radiograph demonstrates two or more "markers" of nerve/canal intimacy.
There is a rule in clinical medicine that states: "Don’t order a test unless the results will influence your treatment of the patient." I fail to see how a CT scan result would alter the treatment of the mandibular third molar already known to have an intimate relationship with the mandibular canal. This information would be obtained from a panoramic or periapical radiograph.
If there is already a strong indication for removal of the tooth, such as those mentioned previously, the surgeon will need to discuss the increased risk of nerve injury with the patient, and alter his or her surgical technique accordingly. In those cases when removal of the third molar is elective, a discussion of the risk of nerve injury would impact the patient’s informed consent.
Occasionally, a patient offered the option might elect to have a CT scan as part of the evaluation process. However, from the panoramic or periapical radiograph, the relationship of the canal would already be inferred, if not known, and the patient and surgeon would know enough to be aware and to take precautions during surgery. A CT scan is an expensive study, not generally covered by health care plans for third-molar evaluation. This would be an unnecessary burden on the already beleaguered health care dollar.
I see the CT scan as a research tool in studying anatomical relationships, rather than as a helpful or necessary standard clinical diagnostic modality for the impacted mandibular third molar located adjacent to the mandibular canal.
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