Find a good dentist who respects you, and VISIT THEM REGULARLY. If you feel pain or sensitivity in a tooth, DON'T LEAVE IT FOR THREE YEARS, GO AND GET IT CHECKED ASAP. It will only get worse - so much worse. Getting a filling done is nothing. Getting a root canal when the first dentist I saw was a dumbfuck and tried drilling into an infected nerve that was still alive (worst pain) has made going to the dentist akin to jumping off a mountain whilst glued to an angry bear for me.

Don't let it get so bad that the treatment scares you into a panic attack, and don't see shitty dentists - you have the right to choose a good doctor or dentist! You're allowed to tell them you're not comfortable proceeding with something! You can ask to see a different one or switch clinics if you need to! Don't wait til you're older to figure this out - take responsibility for your health (and your teeth).

(This is mostly aimed at people in the UK - remember, kids, if you're in full time education and under 19, you're entitled to free dental care. Over 19, a checkup costs £18 ish on the NHS, and most procedures will cost about £55 (which includes the base checkup fee, any x-rays, and as many things as need to be done - fillings, root canals, whatever). If you're not in the UK...I dunno how dentistry works in your country, but if you can afford it, take my advice and get your teeth checked out often!)

Extra advice - make sure you're registered with a GP, and don't be afraid to visit them if something's not right, whatever that might be. Get health problems (and mental health problems) treated as soon as possible - don't leave them to get worse because "It's not so bad..." or "I'm too embarrassed!". IT WILL SAVE YOU SO MUCH PAIN THE LONG RUN TO GET IT SORTED OUT NOW.