Practicing dentist here. Since this is all hypothetical, let me respond with some real world perspective. To answer “how much loan is too high?” question, the answer would be “it depends”... you may also have to consider being an average specialist in that context. Let me give you couple of examples of specialist friends I know;
Friend 1: Graduated with me from the same class in 2010. He did 3 years ortho residency in Colorado directly after dental school. Graduated with a total 600k in student loans. He opened a practice about 5 years ago, paid all off his student loans, owns a home, and makes a decent income about 300-400k/yr. The last 12 months was rough for him; staff quitting for better pay somewhere else (he was paying his financial coordinator 75k/yr, she left him for a better pay, most of his assistants left too for the same reason), he constantly complains about how traditional ortho is still good but some patients are shifting to aligners and treatments in his office slowly moved away from traditional braces. He complains about stagnant dental insurance reimbursements relative to high inflation and the increasing overhead (specially payroll), etc. He doesn’t think ortho was truly worth it from today’s perspective, and if he had known what he knows now, he would pick a different career (maybe in tech?) and make as much money with far less headaches that owning a dental office headaches. He’s 41 now.
Friend 2: Graduated from DS in 2013 with about 250k. Worked about 5 years as a general dentist and couldn’t pay off his student loans with his 180-200k/year income. Used most of his income on nice cars and renting nice pads. He went back to school and specialize in endo at a Midwest program - which definitely hurt his lifestyle from a dentist with an income to a student life again. His endo debt was about 250k, so now he has about 400k in student debt total. He started work as an endodontist 6 months ago and he expects to make about 300-350k his first year, hopes to make 400k second year and probably thinks he will peak at 450k/yr for the following years with his ideal work-life balance. He’s focusing on paying off all his student loans next 2-3 years. He complains about the learning curve and picking up his speeds as a new endodontist now, it can be rough some days at work - he gets a lot difficult cases (calcified canals, etc), as general dentists keep all the easy cases to themselves. He doesn’t own a home yet, he thinks there is a big housing bubble - waiting until prices come down, which maybe few more years. He’s 38 now.
Bottom line, specializing is very hard and comes with additional debt. Both of my friends would have bigger student debt if they were applying to DS and specialty programs today. In fact, the Ortho friend would be looking at 800k-1M total if he applied today as a pre-dent. While the endo friend would be looking at maybe 600k+. I don’t think either of them would rush to specialize if the debt was that high, then again, no practicing dentist could imagine paying more student loans out of their personal finances. Me personally, anything north of $500k is wild and very risky. The world has also changed; we are in a high inflation economy, everything costs more, so imagine taking out a ridiculously high student loans in an environment where dental insurances are not increasing reimbursements, which all adds up to lower net/take home for the average specialist. Not to say the average specialist will not make a good income, but when you combine bigger student debt + higher inflation = the purchase power of any income declines. The specialist $400k income will be worth 5-10% LESS every year in that equation. So do your maths before you make the decision.