The most commonly used local anesthetic is lidocaine (also called xylocaine or lignocaine), a modern replacement for novocaine and procaine. Its half-life in the body is about 1.5-2 hours. Other local anaesthetics in current use include septocaine, marcaine (a long-acting anesthetic), and mepivacaine. A combination of these may be used depending on the situation. Also, most agents come in two forms: with and without epinephrine.
The most common technique, effective for the lower teeth and jaw, is inferior alveolar nerve anaesthesia. An injection blocks sensation in the inferior alveolar nerve, which runs from the hinge of the jaw down the back of the mandible, connecting to the lower teeth, lower lip, chin, and tongue. The inferior alveolar nerve probably is anesthetized more often than any other nerve in the body. To anesthetize this nerve, the dentist inserts the needle somewhat posterior to the patient’s last molar. Several nondental nerves are usually anesthetized during an inferior alveolar block. The mental nerve, which supplies cutaneous innervation to the anterior lip and chin, is a distal branch of the inferior alveolar nerve. When the inferior alveolar nerve is blocked, the mental nerve is blocked also, resulting in a numb lip and chin. Nerves lying near the point where the inferior alveolar nerve enters the mandible often are also anesthetized during inferior alveolar anesthesia. For example, the lingual nerve can be anesthetized to produce a numb tongue. The facial nerve lies some distance from the inferior alveolar nerve, but in rare cases anesthetic can diffuse far enough posteriorly to anesthetize that nerve. The result is a temporary facial palsy (paralysis or paresis), with the injected side of the face drooping because of flaccid muscles, which disappears when the anesthesia wears off. If the facial nerve is cut by an improperly inserted needle, permanent facial palsy may occur.
The superior alveolar nerves are not usually anesthetized directly because they are difficult to approach with a needle. For this reason, the upper are usually anesthetized locally by inserting the needle beneath the oral mucosa surrounding the teeth.
