Will my slightly droopy eye lid go away after swelling from dental surgery?

Swelling that is bad enough can cause persisted ptosis in an affected upper eyelid.  I would advise patience here.  This really could take many weeks and, in rare cases, more time to fully resolve.  While it is unlikely to cause permanent upper eyelid ptosis, this is a remote possibility.  Normally I recommend being assessed by an oculoplastic surgery if the swelling has not resolved in 6 months.  However, I recommend that you go get assessed now given that the side that is droop was not the side where surgery was performed.