The clinical efficacy of local anesthetics is reduced in the presence of inflammation, sometimes limiting the ability to perform necessary therapeutic procedures. Recent studies suggest, however, that opiate receptors are expressed in the dental pulp and oral mucosal tissues and increase in number under conditions of inflammation. The proposed clinical study will assess the therapeutic effectiveness of the opioid, fentanyl, to enhance the profoundness of the local anesthetic lidocaine with 1:100,000 epinephrine when used on inflamed mandibular molar teeth. Delivering lidocaine 2% with 1:100,000 epinephrine intraosseously immediately after delivering fentanyl intraosseously is predicted to increase the success rate of local anesthesia on the inflamed pulpal tissues of mandibular molars. Three different strategies will be studied to assess fentanyl as an adjunct to local anesthesia. The first study will assess the efficacy of individual drugs under normal conditions in patients whose mandibular molars have healthy pulpal tissues. Pulpal anesthesia will be measured by an electronic pulp tester and drugs will be delivered intraosseously. A second study will evaluate local anesthetic success using the same drugs and route of administration in patients whose mandibular molars have inflamed pulpal tissues. Root canal treatment will test for the clinical effectiveness of local anesthesia. A third study will assess systemic side effects using different rates of intraosseous drug delivery. This series of studies may provide a rationale for the adjunctive administration of opioids in clinical conditions where inflammation limits the effectiveness of local anesthetics alone.