"Complications of an Intra-Arterial Injection From an Inferior Alveolar Nerve Block" by Dr. Brian Webber and colleagues described certain side effects of intra-arterial infra-alveolar injections (December JADA).
The case was well-presented, and the authors clearly summarized the literature about the more commonly observed minor—and the rare, potentially more severe—clinical complications from this procedure.
Indeed, in our experience, intra-arterial injection from an inferior alveolar nerve block is relatively common in the daily routine of the dental practice, and thus one may argue whether publication of the original report was warranted. The dialogue it generated in JADA’s April letters to the editor, however, brought to light issues about the correspondence of opinions between basic science and clinical science in dentistry that deserve discussion.
From the perspective of the clinician, it is well accepted that intra-arterial infra-alveolar injections occur when the needle is applied too forcefully, and pierces and penetrates the infra-alveolar artery when performing a mandibular block, as the authors correctly observed. When this occurs, the anesthetic can be inadvertently injected into the arterial blood supply.
For example, we can cite the recent case of a 28-year-old woman treated in our office for restoration in the lower-left quadrant. The needle was inserted gently at the mandibular foramen, immediately inferior to the lingula. Minor positive pressure was applied to ensure that a few droplets of anesthetic would instantaneously induce anesthesia as the needle penetrated.
Whereas the dentist was attentive to feel arterial flow vibrations in the syringe, should the arterial wall be penetrated, a fraction (about one-fourth) of the anesthetic was inadvertently injected to the artery. The needle was removed immediately. Within seconds, the patient exhibited blanching para-nasally and oculomotor disturbances on the corresponding side. The symptoms were of brief duration, and numbness of the lower quadrant was almost immediate. The dentist, fully aware of the situation and of the fundamental basic science behind it, was able to calm the fears of the patient and to take full control of the situation.
The authors correctly, albeit succinctly, outline the fundamental anatomical and physiological underpinnings of this reaction. The authors also correctly invoke the infra-alveolar and infraorbital arteries, and explain that epinephrine, which is generally added to the lidocaine anesthetic in order to extend its action, binds to adrenergic receptors, thus leading to constriction of the blood vessels and to hypoxia. More could have been said, and perhaps should have been said, from the perspective of basic science. However, the fundamentals were correctly presented.
In his April letter to the editor, [the letter writer] most likely misread the original report, and argued incorrectly in favor of the involvement of the facial artery. It is preposterous to invoke the facial artery at this juncture because the facial artery supplies primarily the superficial aspects of the face. While it is true that the facial artery sends deep branches to the tonsillar bed and Waldeyer tonsillar ring, as well as to the submandibular gland, the principal anatomical domain of the facial artery consists of the medial aspects of the face, lips and nose and their respective musculature. The superficial course of the facial artery precludes its potential involvement in the complications of intra-arterial injection of anesthetics.
From the perspective of the basic scientist, however, it is also true that the terminal branch of the facial artery superiorly changes its name to the angular artery because of its course and configuration. Inferiorly, the facial artery descends to become the superior labial artery; this is why the reaction also may include superficial numbness of the upper lip.
Arterioles from the angular artery anastomose extensively with arterioles that arise from the infraorbital artery. It is precisely that anastomose—which lies quite superficially between the zygoma, the inferior border of the orbit and the nasal protuberances—that is responsible for the observed blanching during intra-arterial injection from an inferior alveolar nerve block. Indeed, the anesthetic cannot "flow backward" as [the letter writer] correctly states, nor did, however, the authors ever suggest that it did.
Neither [the letter writer] nor the authors seem to have fully appreciated the fact that the arterial network that results from the anastomosis of the angular and the infraorbital arterioles work in concert to supply the extensive superficial musculature in the perinasal and periorbital area. Nose-associated facial muscles (such as the procerus and the levator labii superioris alaeque nasi), as well as eye-associated facial muscles (including the orbicularis oculi; the corrugator supracilii, in particular its palpebral portion; and, to some extent, the inferior tarsal muscle of the lower eyelid), are affected.
Arteriolar branches also enter the orbit inferiorly to supply the anterior fibers of the inferior rectus and of the inferior oblique muscles. It is of importance to both basic scientists and clinicians discussing the oculomotor manifestations of this reaction to note that the function of the inferior rectus muscles is to depress, to adduct and to medially rotate the eye. The inferior oblique muscle, which aids in superolateral rotation of the eye, also is supplied by this anastomosis, as well as by branches of the ophthalmic artery, the terminal branch of the internal carotid artery. Terminal arterioles from the ophthalmic artery anastomose at that site with terminal arterioles from the infraorbital artery. Therefore, this reaction also can lead to transient troubled vision.
What is most disturbing from this exchange between the authors and [the letter writer] is not the incompleteness of the physioanatomical discussion, nor the incorrect or vague statements about the implication of this or that artery. What is appalling is the use of certain verbiage and the tone of certain statements.
We must learn—basic scientists and clinicians alike—to work together and to learn from each other. We must strive to stop the polite, and at times less polite, mudslinging and back-stabbing. It is true that we view the same "white elephant" from different perspectives. But it is also true that our respective fields of expertise must be complementary and not mutually harmful.
The field of dentistry can and must make greater strides forward for the benefit of the patients in the 21st century. This can only be achieved if both basic scientists and clinicians work together to contribute to the profession—not by belittling but by respecting each other as scholars and as colleagues.
