Would doing an SMP at Georgetown or BU etc be helpful if you wish to go to dental school, especially if your gpa during undergrad was around 3.1?

Sure. You're taking classes that are similar to first year dental school courses. It can only help if you do well, of course. BU should be a top choice since I understand you can take electives with dental students. There are some students on the post-bacc forum who are in this program.

Oh, don't forget SMPs at DO schools. Those can work just as well.

i remember hearing, for some reason, that you were discouraged from attending Georgetown SMP if you are interested in dentistry. you should look into it. i really can't recall the reason. personally, i can't see why it wouldn't help for dentistry. but, you might wanna call up or e-mail the gu smp directors and ask about that.