GPA is mostly meaningless, rank is far more important. Some dental schools multiple students have 4.0's, where at others getting a 3.9 falls just short of being physically impossible.
As far as numbers, who knows. For endo/ortho the gold standard is 90+, but I know some people going into ortho this year with mid-80s. I'm sure there are some perio programs that are fairly competitive, but for most 85+ and top 50% of the class should do you well, maybe even less than that.