and this is what I know ........
Wait, I'll start with my background ......
I've got 10 years active duty as a Naval Aviator and 8 years so far in the Navy Reserves. I'm currently a Commander (CDR) which is an O-5. I'm also a dentist wannabe like you guys. Only I haven't been accepted anywhere yet.
I have looked into the scholarship stuff myself and I'll do my best to pass on all that I know so far. My info comes straight from the Dental Corps Career Planner in Memphis. He is a Captain (O-6) in the Navy Dental Corps which means that he is a dentist, not a recruiter!! Recruiters earn medals and commendations for filling their quotas. You are a recruiter's "bread & butter". ALWAYS take everything a recruiter says with a grain of salt and make sure that any "promises" you've been given are in writing (get a copy of the DOD instruction that states/defines the promise). With that said, here's what I know:
HPSP (Professional Scholarship Program) - This is the scholarship that most people are interested in. You get full tuition paid for (no price cap - University of the Pacific anyone?), a monthly stipend, textbooks & fees (like instrument rentals, etc). I did not ask if that covers the fee for medical insurance, but I do know that you will not be able to get medical care at the local military base because you'll be IRR while in school. (The IRR is the inactice reserve, you accrue time in service but no pay). You are expected to spend 40-45 days on paid actice duty each summer, Shamrock mentioned this. If your school's schedule can't accommodate you leaving, the Navy will just cut you orders to your school where you go about your bussiness as a student except with pay, sweet deal.
So, this is how this works ..... you get a letter of acceptance into a school, sign on the military dotted line (assuming you are granted the scholarship) and are commissioned an Ensign (ENS O-1) in the IRR, then upon graduation you are promoted to Lieutenant (LT O-3). I don't know who told you that you'd be an O-4, but that is NOT correct! (Unless you have prior service AS AN OFFICER and then you get credit for only HALF of your active duty time towards your entry rank.) It is possible that if you specilize you may come in at a higher rank, but it would have to be an extremely under-manned specialty because you are given your authority based on rank. In other words, you can't come in to the Military as an O-4, where they'd expect you to be able to perform as a department head when the only thing you know so far is how to wear the uniform. You can apply for this program AFTER you've started school. It's a year for year pay-back, min 3 years. I've never heard of anyone NOT owing extra time for specializing or for taking longer to get through school. Once they pay the money to train you, they expect to get your expertise in return! [There are programs geared at specialing that can be applied for once you are serving on active duty. I don't know much about them.] The HSCP is great if you want to go to a really expensive school &/or want no debts!
HSCP (Service Collegiate Program) - Once accepted into this program you are an E-6. You earn all pay and entitlements of an E-6 the whole time while in school. Healthcare, COLA, variable housing allowance (VHA), etc. But you pay for school, books, etc. And, No, you don't need to wear the uniform. Besides, even if you did, the Navy dentists wear scrubs! Then when you graduate you are commissioned an O-3.
In the Navy you can expect to be stationed somewhere for one year where you will rotate through all the departments for experience, like a residency without the certificate. Places like Great Lakes, Miramar, Bethesda, etc. Once that year is up you will get orders to go operational. This means on a ship, to Japan or over to the sandbox with the Marines. Yes, the Marines fall under the DoN, but don't tell them that, it fries their little Jarhead brain!
I have no idea if the other services handles their "newbees" this way. NONE of the services will pay for you to set up a private practice once your commitment is up!
Positives about Navy life: It's a really awesome experience. You'll go places you'd never see otherwise and live in places that you'd never imagine.
The Navy is the biggest and strongest fraternity in the world. You'll make friends that quickly become family, for life. If you have a family that you're leaving behind while deploying, there's a huge support network. You're never alone if you don't want to be.
Negatives: If you are married &/or have kids be prepared for long separations. You'll go places you'd never see otherwise and live in places that you'd never imagine.
Six month deployments if attached to a boat, possible 1 year "unaccompanied orders" overseas when the need arises. But, the needs of the military always come first. You may be offered a choice of a few places to go, choose one and then get the other. There's an old saying in the Navy that "Timing is Everything".
With that being said, make sure that you are certain about your decision before you sign on the dotted line. There is a war on and who knows when it will end. There are some military programs out there that pay back your student loans after school and then you owe them service. If you're uncertain about commiting now, look into those. Or wait a year and then decide. I hope this helps and good luck!