The debt is massive, but most of us will come out of school with it hanging over our heads. You need to sit down and run the numbers, including the interest that will be compounded into your loan at the end of your four years, and see how much of your future dentist-lifestyle you are willing to sacrifice for your life in dental school. I compared Indiana and Penn, borrowing everything, and it came out after four years to be $200,000 and $400,000. This means about $2000/month payments or $4300/month payments over a 15 year period. Sounds like a lot, right? Be sure to then calculate how much money you will have at the end of the month by subracting that, taxes, and all the other expenses you will or might have once you start working from an average salary. If it doesn't seem like you'll really miss that 1,2, or 3K a month that you have to put toward your loan, then go to the place you will enjoy more!
One more thing to think about, though: how much money could you be making off of investments with that money you will have to instead put toward a loan because you went out of state? Even 12k a year over a 15 year period at a measly 4% will give you close to 300k!
I know this all sounds very miserly, but we are all going to be thinking about this when we have house+cars+practice+family+livestyle to pay for, and this is the only quantitative way to consider this question (the in-state or private question). Of course, there is no way to put a number on 4 years of your life. . .