Is it painful when they drain a dental abscess at the dentist office?

Opposite-relief!: Since there is "pus under pressure" in a dental abscess, you will find that the release of this pus by incision and drainage, will provide you with a remarkably quick way of relieving the "pain" of the abscess.

Usually not: Unless you are not able to get numb usually a dental access should be drained and should be painless although they may put you on a strong a/b one day before the procedure.

Depends: A superficial abscess appearing adjacent to the tooth with no limitation or pain with opening your mouth can usually be drained with minimal discomfort. Incising and draining a dental abscess that has now involved deeper structures of the jaws or cervical spaces with limitation of opening could be quite painful unless you are deeply sedated or under general anesthesia.