Do I Need to Use Both Top and Bottom Invisalign?

In many instances both upper and lower teeth do need to move together even if the upper teeth look relatively straight. It is important that in the end of treatment your bite fits properly and that could be hard to accomplish with only one arch moving. You should review it with your orthodontist to see if it is a possibility in your particular situation.

You really should have gone over this with your doctor before approving the Invisalign treatment.  One arch treatment is sometimes done, but if your treatment for the lower involved changing the arch form you might have interferences with the upper teeth unless you change the upper alignment at the same time.