ok... so I'll start: your dental school grades/ranking/test scores (just like in the civilian side) + your time in the military and whether you have done a 1yr AEGD/deployed/etc
Goes without saying: no failed PT tests, no bad OERs, no bad counselings
Unless you are a stellar dental student, you are much more likely to have to work a few years as a GP before you start (which is actually a GOOD thing)