Hey Crystal , for me it is intermittent,the reason is the motor Neurons for the facial muscles as well as the throat are affected (speech ,swallowing, chewing )not the jaw so much ,as the jaw is a bone ,only problem with jaw might be TMJ Temporal Mandibular Jaw Syndrome ,theres a muscle that holds the upper jaw to the lower one ,if this gets weak it allows the jaw to become disjointed . Havent heard much of that and PLS . I also have it happen when i yawn ,my mouth snaps shut real fast and i get the cheek in between the teeth .Mostly for me on the right side, never chewed on my left cheek . Also when i sneeze i get lots of Saliva and my teeth snap shut fast (lack of facial muscle control when it needs to react fast )Geo