The envelope of function
Controversial topic so depends on who you ask as to what exactly it is and when exactly it is important. Like many things that are controversial, the answer to any question about the topic is likely, “It depends,…..”.
When should you check for the envelope of function?
Check the envelope of function before big case (especially the ones with anterior wear), when big cases are in temps, and prior to final delivery of these cases. These are usually the same cases that get a deprogrammer for a week to check how close they are to centric.
How can you check the envelope of function?
One method to check is to place a piece of 200 micron articulating film (Bausch) in patients anterior and have them chew on gum in the back. Any marks on facial of lowers and lingual of uppers are interferences, because the gum is keeping the posteriors slightly apart.
Another method from from John Nosti is to have the patient to sit up, lean forward a little and look down as if looking at a dinner plate. Place red articulating paper in and have the patient open wide and close down fast. Then keep their mouth open, and lie them back in the chair and recheck with the blue articulating paper. Any red marks that are in front of the blue marks you adjust by hollowing our the palatal contour between the two marks so they are the same vertical. This is the “freedom” in/from centric or long centric. A lot more can information can be found in Dawson’s books on these topics. Kois and Dawson are the two that speak and write about envelope of function the most.
What are the issues with restoring into the envelope of function?
Most patients will likely adapt fine but you are putting unneeded stress on the restoration in the way and on the muscles and joints. Patients may complain that they hit their teeth when they chew or bite a certain way.