For an infiltrative injection on the lingual aspect of tooth #13, what is the injection site?

• A. Apex of the tooth
• B. Pulp chamber
• C. Cervical area near the CEJ
• D. Root apex of adjacent tooth

Answer: (A)

An infiltrative anesthesia for a single tooth is delivered near the tooth’s apex so the drug can diffuse through the surrounding cancellous bone and block the apical nerve fibers that supply that tooth. For a lingual infiltration on tooth #13, the correct site is at the lingual mucosa directly over the root tip, i.e., at the apex. This places the anesthetic where it can reach the nerves entering the tooth and provide both pulpal and surrounding tissue anesthesia. Depositing into the pulp chamber isn’t appropriate and won’t reliably numb the surrounding tissues. A site near the CEJ isn’t where the apical nerves are concentrated, and injecting at the apex of a neighboring tooth would not adequately anesthetize the target tooth.