All injectable dental local anesthetics available in North America today are amide local anesthetics.
These agents are safe, nonallergenic, usually metabolized in the liver, and excreted by the kidneys.
They are also mild vasodilators, which result in an increased rate of anesthetic absorption into the bloodstream, an increased risk of systemic toxicity, reduction of duration of action, and increased bleeding in the area.
Vasoconstrictors are added to local anesthetic agents to counteract the vasodilatory properties. By constricting the blood vessels in the area, absorption is decreased, resulting in reduced risk of systemic toxicity, increased duration of action, and increased hemostasis.
► See also: Guideline on Use of Local Anesthesia for Pediatric Dental Patients
Youtube / Dental Minute with Steven T. Cutbirth, DDS