Why is infiltration often less effective for pulpal anesthesia of mandibular teeth?

• A. The dense cortical bone and limited diffusion to the nerve
• B. The rapid clearance by venous drainage
• C. The teeth's nerve fibers are resistant
• D. The mandible has no cortical bone

Answer: (D)

Infiltration works best when the anesthetic can diffuse through bone to reach the nerve fibers near the tooth. In the mandible, the outer layer is thick, dense cortical bone with limited cancellous space around the roots. That strong barrier makes it hard for the solution to diffuse to the nerves inside the mandibular canal, so pulpal anesthesia is less reliable. The idea that the mandible lacks cortical bone isn’t true—the mandible actually has substantial cortical bone, which is exactly why infiltration is less effective there. Venous drainage and inherent nerve resistance aren’t the primary factors limiting infiltration in the mandible; diffusion through the dense bone is the main obstacle.