If I had a 3.5, I would feel relatively safe with a 20, since that's slightly above average for matriculants. That would make you an average applicant in that respect, and get you interviews most likely. With those stats, you are probably going to dental school.
Each point below on GPA and I'd want to add around a point to the DAT score (3.3/22), but that's not solid since a 3.0 with a 25AA can raise suspicions (or so I've heard).