what are the benefits to going to a top dental school ? I would want to get into OMFS , endodontics or pediatric dentistry. Would going to a top dental school help with specializing ? What is the cost cutoff where you settle for your state school over a top tier UPenn or Harvard ?
You'll benefit the economy, as you'll put an extra few hundred thousand dollars back into circulation through the extra tuition you'll have to pay (over cheaper state schools) that will go to finance new Mercedes for the faculty.
On a more serious note, just by numbers, more students specialize from "top" schools (defined by academic reputation and not by clinical excellence) than from cheaper state schools. Whether this is an effect of the "top" school's reputation, research opportunities, connections, etc. (in which case the school does provide an actual advatage) or just a reflection on the quality of students they attract (in which case those same student can go to cheaper schools and get into the same specialties) is a matter of debate. It is likely you will have to work harder in a cheaper school, though, if you want to specialize, because you'll probably have to be at the top of your class.
So, is avoiding that hard work and having a slightly less chance of being able to pursue your dream speciality worth 250k to you? There are some scenarios it may be, such as if you're dead set on a particular specialty (like if you come from a family of orthodontists and have seen other areas of dentistry and know ortho is the only way for you). In most cases, though, it probably isn't. But it's up to you.
And there is no fixed "cost cutoff" for "settling" for a state school. In the first place, many (most?) people don't settle for their state schools, they prefer them, not only due to cost but also due to clinical excellence (they want to know how to do actual procedures instead of how to recite the Krebs cycle by heart). But if it is a settlement for you, think about how much the advantages of a "top" school are worth to you. Must people would say not more than 100k, and I think that makes sense in general as well, but, once again, it depends on your situation. They might be worth more than that in some situations (like my example above) and less than that in others.