A couple of days
Tenderness is completely normal and expected when orthodontic therapy of any kind is performed. It is, however, usually much less tender with Invisalign compared to Conventional Orthodontics. If you just got your first set of aligners, tenderness will be evident for the first couple of days and then you will not feel any more until the second set of aligners is placed in about 2 weeks. With each set of aligners, tenderness becomes less and less. For any of my patients who have experienced any tenderness, they have reported that the tenderness goes away within the first couple of days. If they needed anything for the tenderness, they only had to take Tylenol or Advil. Tenderness from conventional braces when wires are tightened can be much more painful and last for many more days then what you're experiencing with Invisalign.
Douglas Jopling, DDS Dallas, Texas area