Why Your LeForts Have Asymmetric Interferences
“Where you stand determines what you see. What you see determines how you cut.”
notice the upward angle of the saw blade
Easy cuts are ergonomically natural. Hard cuts are ergonomically confusing. Implant placement in site 12 is easy. The same surgery in site #18… feels like a completely different surgery.
The LeFort osteotomy is simple… but the 2D image of a symmetric diagonal cut doesn’t do justice in teaching you the technique. In the same way, a LeFort osteotomy on the right side is a completely different “cut” than the left side—unless you are ambidextrous. The LeFort cut isn’t just the line you create in the anterior maxilla, your angulation also affects how you cut further medially.
Source: Posnick, Jeffrey. Principles and Practice of Orthognathic Surgery
This is typically how it goes, you are standing on the right side cutting the right side. Left hand is holding the toe out Langenbeck in the pterygoid plate pocket and right hand holding the saw.
You’ll notice that you can’t look at the cut from over your hand without standing all funny, and you’ll find that is is more natural to look towards the palmside of your hand—and to do so, your body will lean to the left. In this view and stance, it feels natural to cut with a saw pointed downward (towards the root tips). And as you cut posterior to anterior, it is easy to maintain this angle.
You’re looking down the saw, while pointing the saw down. Makes sense.
On the left side, it’s a different story. Now you are standing on the left side, cutting the left side… but with your right hand. Now instead of looking down, you are looking up at the saw—and your body will again lean left. Because pronation feels more natural than supination, you hand will naturally tilt “left” (pronate towards you), which will direct the tip superiorly.
Since you are so focused on making a symmetric cut, avoiding a lip laceration, and puncturing the NT tube, you won’t notice this subtle angle change - the cuts look symmetric-looking after all!
After the downfracture, however, you will notice the difference in interferences. Rongeur away…
Source: Reyene, Johan. Essentials of Orthognathic Surgery.
Does this matter? Well… no, but it adds inefficiencies to your surgery.
What could have been little snip snip with the ronguer and profiling with the egg bur, now becomes the interplay between right and left side trying to see where you are interfering.
Remember posterior interferences are mostly blind and located by tactile feel… and this difference in angulation affects the posterior interferences. If you overclose against psterior inteferences, it displace your condyles but everything still looks right (MMF is still on point, bony contact everywhere, incisal show, etc)
