The Frankfort horizontal line may be useful in radiology or orthodontia but not in prosthetics. It is used in anthropology as a means to compare different skulls and in orthodontics to study skull growth.
It runs from the orbitale, the lowest point on the rim of the bony orbit, to the porion, the most lateral point in the middle of the bony roof of the external auditory meatus.
To get the Frankfort horizontal plane the two porio and the orbitale are used.
To make matters more complex, since the porion is hard to determine on a person, the tragion is used. The term tragion relates to the tragus of the ear.
The tragus is that part of the outer ear just in front of the external auditory meatus which points backward and outward. The tragion lies about 2.5 mm above and in front of the porion. Consider the tragion to be at the top of the tragus.
What is the Frankfort horizontal line? It is a line drawn through the orbitale and the tragion. (It runs from the bottom of the eye to the middle of the ear.) Don't confuse it with another line that is related to the occlusal plane.
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©1999 by Julius Rosen, D.D.S.