Where is the insertion site for an ASA nerve block?

• A. Height of the mucobuccal fold directly over the first premolar
• B. Over the canine fossa
• C. At the midline of the maxilla above the central incisor
• D. Near the mental foramen

Answer: (A)

The key idea is targeting the anterior superior alveolar nerve as it travels toward the maxillary anterior teeth. For the ASA block, you want the anesthetic deposited in a spot that sits along the nerve’s path near the infraorbital area so the anesthetic can diffuse to the ASA nerve trunk before it branches to the teeth and facial gingiva.

Placing the injection at the height of the mucobuccal fold directly over the first premolar positions the needle near the route of the ASA nerve as it approaches the anterior maxilla. From this location, the anesthetic can reach the ASA nerve to numb the maxillary central incisors, lateral incisors, and canines, along with the associated facial gingiva.

In contrast, injecting over the canine fossa tends to target different tissues and is not the most reliable route to the ASA nerve. A midline injection above the central incisor would not effectively block the anterior superior alveolar nerve, and a site near the mental foramen targets the inferior alveolar nerve instead.