Objectives. To determine the length of needle that should be advanced beyond the distance to the lateral pterygoid plate to reach the mandibular nerve.

Methods. The study was conducted on patients and skulls. Patient study: Distances from the skin at midpoint of the zygomatic arch to lateral pterygoid plate and to the point where mandibular nerve paraesthesia occurred were measured in 74 patients having mandibular nerve block for treatment of neuralgic pain. Osteologic study: Distances from the midpoint of the zygomatic arch to lateral pterygoid plate and to a probe inserted vertically into the foramen ovale were measured in 76 dry skulls.

Results. Patient study: The distance to the point where mandibular nerve paraesthesia occurred was more than that to lateral pterygoid plate by 0.07 cm on right and 0.11 cm on left. Osteologic study: The distance to the probe in the foramen ovale (representing mandibular nerve) was less than the distance to lateral pterygoid plate by 0.08 cm on the right and 0.07 cm on the left.

Conclusions. There is no osteologic basis to advance the needle beyond the distance to the lateral pterygoid plate to reach mandibular nerve. However, because the needle may contact the nerve at variable points rather than the shortest distance to the nerve, the needle may be advanced by 0.07 cm on the right and 0.11 cm on the left side in patients. This increase is much less than that indicated in the standard textbooks. Therefore, while performing mandibular nerve block, we suggest caution in advancing the needle beyond the distance to lateral pterygoid plate.