Dental anesthesia is comprised of a spectrum of different types of anesthesia that includes not only local anesthetics, but sedation and general anesthesia as well.
The most commonly used anesthetic in dentistry is lidocaine, a modern replacement for novocaine and procaine. Its half-life in the body is about 1.5–2 hours. Other local anesthetics in current use include articaine, septocaine, marcaine (a long-acting anesthetic), and mepivacaine. A combination of these may be used depending on the situation. Most local anesthesia agents come in two forms, with and without epinephrine.
The most common local anesthetic technique, effective for the lower teeth and jaw, is inferior alveolar nerve anesthesia. The inferior alveolar nerve runs from the angle of the mandible down the medial aspect of the mandible, innervating the lower teeth, lower lip, chin, and tongue. An injection of local anesthetic directly into this nerve blocks sensation. To anesthetize this nerve, the dentist inserts the needle somewhat posterior to the patient’s last molar Figure 1. Several non-dental 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), 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 can occur.
The superior alveolar nerves are not usually anesthetized directly because they are difficult to approach with a needle. For this reason, the upper teeth are usually anesthetized locally by injecting lidociane beneath the oral mucosa surrounding the teeth.