If you want to give your kids the same comfortable lifestyle and debt-free education like what your parents are giving you right now, then I don’t think an income of $120k/year is enough. In order for your kids to go a good junior/high school, you either have to purchase a more expensive house in a safe area with good school district or to put your kids in expensive private school. Most dentists work as an independent contractor. This means that you will have to pay for your own health insurance (it’s $1200/month for a family of 4 right now….and it will probably be around $2000/month by the time you get married and have kids), malpractice insurance, disability insurance, 401k etc.
I know this optometrist couple whose combined income is easily over $120k/year. Their eldest son will attend UC Davis (a public university) next year. According to them, their son’s first year (tuition + room and board) will cost them at least $25k. They told me that can only afford to pay for their 2 kids’ undergrad education. Their kids will have to take out student loan when they go to dental school (one of the sons wants to be an orthodontist like me). The husband has his own practice and still drives a 10 yr old Honda Pilot. And the wife still works F/T for Kaiser’s optometry dept. Both of them will turn 50 next year.
With $120k/year income and no plan to open up your own practice, you may have to work until you are 65+ years old. As you get older you may make less because of your declining health (you said earlier, you didn’t want to hurt your back from over-working) and increase in competition among dentists (due to opening of new dental schools).