Most often, before getting private loans, you can make adjustments to your budget to increase your unsubsidized loans. They don't include things like medical insurance or normal rent payments, so the budget can be adjusted for certain expenses.
Most dental schools do include both of these things in their estimated budgest. However, you would need to increase your budget if certain things come up that the school allows, such as car repairs, childcare expenses, or heating.
Most government loans cap out at around $38,500-40,000. If this exceeds your expenses for the first year, you first accept all the loans you want to from the government (all they give, so that you take out the fewest private loans possible) and you THEN apply to the private loans. You can ask the school which bank they're in cahoots with
....most schools have associations with a few banks who trust the schools budget and will usually add the difference that the government loans didn't spend, without you really having to prove anything.
I can't speak for anyone else, but be careful to not borrow too much. I know that everyone complains about not having money, but it can be worse to have too much, especially if it's in the private loan and you're paying 12% interest (like me.) Even if you realize you have excess and you pay it right back, you've still paid interest on that amount.
So basically, don't always trust your school's budget...obviously, you need to pay them all the tuition and fees they ask for but consider if you'll have a roomate, a significant other who works, or something else that may reduce or increase your living expenses.
And you won't see the private loan money either until it goes through the school, as some other posters said. You just have to trust that school will give you your proper amount back.
One more thing: if you attend a public school and become a resident before you graduate, you probably won't have to take out private loans for the years that you're a resident. The best thing to do in that situation, is to
borrow the remainder of your private loan from the government and pay it back. Sure, you took out more than you needed, but it's at MUCH lower interest than the private loan. (which you've paid back anyway)