Well that depends how good you are at running your business. Staff is usually somewhere in 20%?? of OH. I hear the average OH for dentists is ~60% but some get it down near 50%. This from my sparse readings on dentaltown, they'll have better topics when it comes to overhead.
But if overhead is 60% and you gross $600,000, you (the dentist) nets $240,000 - assuming you take all of the profit for yourself and don't reinvest any into the practice.