Morphological characteristics of the infraorbital foramen and infraorbital canal using three-dimensional models

Infraorbital nerve blocking through the infraorbital foramen and infraorbital canal is used to anesthetize the lower eyelid, upper lip, lateral nose, upper teeth and related gingivae. For this, it is important to know the position of the infraorbital foramen, structures around the foramen, and the direction of the injecting needle related to the angle of the infraorbital canal. Many reports have described the anatomical location of the infraorbital foramen; however, not many have described the angle of the infraorbital canal and those structures around the infraorbital foramen that help the physician visualize the correct direction of the needle. Dried skulls of 42 Korean subjects (27 male and 15 female) were studied to analyze structures around the infraorbital foramen. The morphology of the infraorbital canal was also investigated using three-dimensional models. Structures around the infraorbital foramen were classified into four types according to the existence of a distinct tuberosity above the infraorbital foramen, and the degree of prominence of the canine fossa. Types I and II have a tuberosity above the infraorbital foramen, whereas types III and IV have no distinct tuberosity. Types I and III have a prominent canine fossa, whereas this is less prominent in types II and IV. We analyzed the skulls based on the angle of the infraorbital canal to the median plane. We compared the left and right sides and analyzed differences between the sexes, the three canal shapes, and the four structure types around the infraorbital foramen. Type IV was the most common in this series (38%). The infraorbital canal could be classified into three morphologies: 'tube-like' (69%), 'funnel' (25%) and 'pinched' (6%). The mean angle of the infraorbital canal relative to the median plane was 12°, and the angle relative to the Frankfurt plane was 44°. The mean angle between the infraorbital canal and the Frankfurt plane was 4° larger in males than in females in this series of Korean subjects. The operator of the infraorbital nerve block should pay attention towards directing the needle upward at an angle of about 44° for avoiding nerve damage and consider the different angles of the canal according to the individual's sex.