Final answer:
The primary concern when injecting the masseter muscle is to avoid the mandibular foramen and the nearby lingula to prevent nerve damage and maintain proper movement of the jaw.
Step-by-step explanation:
When injecting into the masseter muscle, a primary concern is avoiding the mandibular foramen, which is an opening on the medial side of the ramus of the mandible. This foramen leads into a tunnel down the length of the mandibular body, where sensory nerves and blood vessels that supply the lower teeth pass through. To effectively numb the lower teeth for dental work without causing unnecessary complications, an injection of anesthesia should be placed into the lateral wall of the oral cavity, specifically at a point before the sensory nerve enters the mandibular foramen.
Furthermore, due to the location of the lingula, a small bony flap next to the mandibular foramen, care should be taken to avoid this area during the injection. The lingula serves as an attachment point for a ligament that helps in the opening and closing of the mouth. Incorrectly injecting into this area could potentially damage the ligament or interfere with the mandibular nerves, leading to complications such as altered sensation or impaired movement of the jaw.