Can't help you with pilot/dentist, but I'll try and do pilot/MD for you.
I won't tell you to be a dentist and fly GA planes on weekends. For some of us, that simply isn't enough.
Firstly, what's your background? Are you a high school freshman or a college junior?
Timeframe to money: In med, you're doing 4years of school then at least 3 years of residency. After those 1st 4 yrs, you'll typically have quite a bit of debt to pay off, while getting 30-40k during residency.
In aviation, you should be able to get all your ratings within 2 yrs of college graduation. You should be able to make 30-40k 2 or 3 years after that.
As a resident, you'll work 80 hours a week. As a pilot, you'll fly 80 hours a month. Your duty time will be longer, but it won't be 320hr/month. Many residents dislike the fact that they make ~$10/hr.
You've got to look at job security. A medical degree is recession-proof. You'll always have a job. Somewhere. You may not be able to change your car every year during the bad times, but you certainly won't starve. Not so with aviation.
Also consider "professional seniority". You can leave a senior position at one hospital for an equivalent position at another hospital. In aviation, generally, if the most senior captain at British Airways leaves to fly for Pinnacle, he will be the most junior FO.
Lastly, ask yourself which one you'd rather do for free. Of course you should NEVER give professional services freely (except for charity), as you have worked long and hard to attain your professional status. However, the question can be useful in helping you to decide.
Of course, one could also ask why not do both? You'd have a great skill to fall back on either way.