It will depend ultimately on each individual; most people use the Functional Activator without any discomfort. However, as with any other oral appliance, it may take an adaptation period to get used to it. It's perfectly normal to experience some soreness in your jaw, teeth, and gums during this adjustment phase. But if you have discomfort that doesn't fade after a few hours of removing the Functional Activator, then we recommend that you seek our team for support at orders@posturepro.co.