Which nerve provides sensory innervation to the mucous membrane of the sinus, alveolus, PDL, and pulpal tissue of the first through third molars?

• A. Branch of PSA that enters the maxilla
• B. MSA
• C. ASA
• D. Infraorbital nerve

Answer: (A)

The nerve responsible is the posterior superior alveolar nerve, a branch of the maxillary nerve. It travels into the maxilla and then sends dental branches to the molars, their periodontal ligament, and the pulpal tissue of the first through third molars. It also carries sensory fibers to the mucous membrane lining the maxillary sinus, which is why it innervates both the sinus mucosa and the molar region.

The middle superior alveolar nerve supplies premolars (and sometimes the MB root of the first molar), not all molars. The anterior superior alveolar nerve serves the canines and incisors, not the molars. The infraorbital nerve is a larger trunk that gives rise to the anterior and middle superior alveolar branches, but the direct innervation of the molars and sinus mucosa is the posterior superior alveolar nerve.