If you plan on specializing, acceptance to the specialty or residency programs are much easier through the military because it is a lot less competitive. There aren't that many students in HPSP (which is the military scholarship) which means there's less people applying for these residencies. Plus, these students in HPSP are spread out in 3 different branches and each branch has their own specialty programs.
Let's say there are 100 scholarships for the Army (I think that's how many they had this year). They have 8 spots open for OMFS. There's a few for perio. Few for prosthodontics. Few endo. And a couple for ortho and ped (there's less ortho and ped residencies since they aren't needed as much in military). So you're only going to be competing against 100 people for your residency program (actually a little more because some people already on active duty will apply too). But of those 100 on HPSP, not all are going to apply for a residency. And even those that are applying for residencies, a lot will be applying to a different program than yours. Say you want perio, there will be many others applying for OMFS, Endo, etc.
I've talked to a couple of dental students who had a way of paying for dental school and they didn't have to take out loans and they were still contemplating the military because it is that much easier to specialize if you go through them.
Also, if you do OMFS, which is a 4 year program, you will still only have to serve 4 years of active duty when you get out. It won't be added to the 4 years of dental school because you can pay off the years in dental school and years in residency at the same time. So if you had only a 3 year HPSP scholarship (if you went to UOP or just paid for your first year of school) and did a 4 year OMFS residency, you would still owe 4 years instead of 3 because of your residency. So essentially, whichever program takes the longest is the amount of years you'll need to pay back on active duty.
One more thing, from reading other threads, I think you have to do at least one year as a general dentist in the military straight out of dental school before you can apply for a residency. So say you do OMFS. You will end up doing 5 years active duty because you will do 1 year active as a general dentist, 4 year residency, then 4 years of active for OMFS (the 3 years you'll have left over to serve for d-school will be fulfilled while you are serving for your residency since you pay off both obligations at the same time). But if you do a shorter residency then you still may need to do only 4 years on active duty because 1 year as GD, 2 years for perio (let's say), and then you'll still only have 3 years left to serve for d-school (your obligation for perio will be fulfilled while you are finishing up your 3 other years for d-school).
