Which bone characteristic makes infiltration anesthesia less effective in the mandible?

• A. Higher bone density
• B. Higher bone porosity
• C. More vascular supply
• D. Larger marrow cavity

Answer: (A)

The key idea is that infiltration anesthesia must diffuse through the surrounding bone to reach the nerve fibers. Bone density and porosity determine how easily that diffusion occurs. In the mandible, the cortical bone is dense and thick, acting like a barrier to diffusion. Because the anesthetic has a hard time penetrating that dense bone, it less reliably reaches the nerve endings, making infiltration anesthesia less effective.

In contrast, areas with more porous, cancellous bone allow the anesthetic to diffuse more readily, which is why infiltration tends to work better in the maxilla. A larger marrow cavity or greater vascular supply can influence diffusion or uptake in other ways, but the dominant factor limiting mandibular infiltration is the higher bone density.