In the end it all boils down to regret. If you become a dentist and leave commercial aviation behind, will you wake up as an old man and regret not chasing that dream? Will you go to sleep wondering what it would have been like to fly that 777 or 747?
There are no guarantees that you would make it, but then there are no guarantees that you'll get through dental school either. Plain and simple, it could all blow up in a second and not turn out the way you wanted it. Sometimes you have to take a leap of faith and go for what you want. Imagine yourself in a successful practice, gobs of money, all the toys you want and flying a shiny new Mooney on the weekends. While flying that Mooney you hear the airliners above you on the radio. Are you envious or happy with your sports car of a piston single?
It is human nature to think the grass is always greener on the other side. Money isn't everything but it sure doesn't hurt. It all comes down to you. Do you want to adjust braces for 35 years or fly airplanes for less money? Do what you think will give you no regrets when you are an old man in front of the fire. Good luck with your decision!