Local anesthetics in dental practice

Local anesthetics are the most widely used drugs in dentistry today. Knowledge of the pharmacology and toxicology of these agents will result in their intelligent and judicious use. The choice of local anesthetic should be individualized for each patient. The duration of the dental procedure should be weighed against the duration of action of the local anesthetic; a decision should be made as to whether a vasoconstrictor is needed to prolong its action. However, if the duration of numbness is too long, the possibility of self-mutilation must be considered in certain patients (for example, children and the mentally retarded). In other patients with whom postoperative pain is expected, it may be beneficial to administer a long-acting local anesthetic such as bupivacaine for control of postoperative pain. The total dose of local anesthetic and vasoconstrictor must be determined for each patient based upon body weight; the maximal dosages for each agent should be known. Small children or frail individuals will require below average dosages. The use of a vasoconstrictor may constitute the limiting factor to the total number of local anesthetic cartridges that can be administered safely over a given period of time. Certain medical problems, such as cardiovascular system impairments or hyperthyroidism, may influence the choice of anesthetic and the quantity of vasoconstrictor. An understanding of the physicochemical properties of local anesthetics is also important to a rational process of selection. There are several causes for failure to achieve profound regional anesthesia. These include inflammation and/or infection, anatomic variation, intravascular injection, accessory innervation, and deflection of the needle. Inflammation and infection reduce the efficacy of a local anesthetic by reducing its bioavailability. Local anesthetics with low pKa values (for instance, mepivacaine) are the most effective in this clinical situation. Other causes of inadequate regional anesthesia are primarily related to technique of administration and can be circumvented by the use of the periodontal ligament injection. A comprehensive review of this technique and its application has been presented by the Council on Dental Materials and Equipment of the American Dental Association. Occasionally, a clinician may be unsuccessful at achieving regional anesthesia despite these additional measures. Highly anxious dental patients or patients with a genuine tolerance to local anesthetics normally pose the most problems. Transitional block or threshold block phenomena should also be suspected in these situations.(ABSTRACT TRUNCATED AT 400 WORDS)