Background and Objectives To determine the length of the needle that should be used to reach the maxillary nerve after the lateral pterygoid plate has been contacted.

Methods The study was conducted on patients and skulls. Patient study: The distances from skin at the midpoint of lower border of zygomatic arch to lateral pterygoid plate and to the point where a paresthesia in the distribution of maxillary nerve was obtained were measured in 75 patients. Osteologic study: The distance from the midpoint of lower border of zygomatic arch to lateral pterygoid plate and to a probe inserted from the orbital aspect through the inferior orbital fissure and pterygopalatine fossa into the foramen rotundum (representing maxillary nerve) was measured in 120 skulls.

Results Patient study: The distance to the point where paraesthesia occurred was more than that to the lateral pterygoid plate by 0.21 cm on the right side and 0.22 cm on the left side. Osteologic study: The distance to the probe in the pterygopalatine fossa was more than the distance to lateral pterygoid plate by 0.13 cm on the right side and 0.14 cm on the left side.

Conclusions The needle should not be advanced by more than approximately 0.25 cm beyond the distance to the pterygoid plate while performing maxillary nerve block by the lateral extraoral approach.