Master of Science
Anatomy & Neurobiology
George W. Burke, Jr.
One of the most commonly experienced symptoms in dentistry and one that is of major concern to the dentist is pain. Since pain is manifested when an environmental change occurs causing injury to responsive tissues, it is often spoken of as a protective mechanism.
Pain has been described by a variety of terms: sharp, burning, aching, cramping, dull and throbbing! (Monheim, 1969). Therefore, it is a difficult term to define. Monheim (1969) describes pain as an unpleasant sensation created by a noxious stimulus that is mediated along specific nerve pathways into the central nervous system, where it is interpreted as pain.
Local anesthetics are drugs that will temporarily interfere with conduction when absorbed into the nerve. A blockage of the afferent transmission produces analgesia, while interruption results in motor paralysis.
Local anesthetic compounds are the most widely used drugs in dentistry and all are synthetic compounds with the exception of cocaine which no longer is used because of its unusual high toxicity. Structural changes in the molecules of these drugs alter the toxicity, potency, diffusibility, profoundness, and duration of anesthetic activity of these compounds. Frequently, as the length of the anesthetic molecule increases, so does its anesthetic activity. Also, structural changes in the molecule may increase toxicity or irritancy without increasing potency. In most cases toxicity tends to rise as potency increases.
Monheim (1969) has suggested that ideal local anesthetics should possess the following properties:
(1) Its action must be reversible.
(2) It should have a low degree of systemic toxicity.
(3) It should have a rapid onset and be of sufficient duration to be advantageous.
(4) It should have a potency sufficient to give complete anesthesia without using harmful concentrated solutions.
(5) It should have sufficient penetrating properties to be effective as a topical anesthetic.
(6) It should be relatively free from production of allergic reactions.
(7) It should be stable in solution and readily metabolized by the body.
(8) It should be either sterile or capable of being sterilized by heat without deterioration.
(9) It must be non-irritating to the tissues and produce no secondary local reaction.
No local anesthetic in use today fulfills to perfection all of these requirements.
Since local anesthetics are the most commonly used drugs in dentistry for routine procedures when anesthesia is desired, it is of particular interest to study the morphologic changes in the muscles that are situated in close proximity to major sensory nerve fibers to the teeth. It is also of interest to question that local anesthetics are non-irritating to the tissues; in fact, they do produce a definite and precise lesion.
Another point of interest is to use and apply local anesthetics to produce a definite lesion clinically to aid in the treatment of a common dental syndrome, the myofacial pain dysfunction syndrome formerly known as Costens Syndrome.
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