I am only 20yrs and having false teeth already at the front and i try everything to care my teeth but is still rotten away what can i do to avoid this?

You need help: It's bacteria that damage teeth. You need to find a good dentist, one that will take the time to help you learn how to care for your mouth. Talk to the dentist about flossing, Fluoride rinses, electric toothbrushes, water piks, disclosing tablets, and whatever else the dentist recommends. You can't do this alone...Find help.

A few thoughts..: If you've already lost some anterior teeth at 21 years old, i suspect that there are many other dental problems on your other teeth. You stated that you've tried everything... Does that include seeing your dentist every 4 months for check-ups and cleanings? Proper diet, home care, and professional monitoring of your dental health is necessary. Follow your dentist's advice.

Medication issues?: While you have indicated that you are not taking medications, many people do not associate "doing street drugs" especially methamphetamine as "medications." I have seen cases of perfectly healthily, dental hygiene oriented patients rapidly lose their teeth, more descriptively "have them rot out" from "meth mouth." interestingly, not a single patient "owned up" to using drugs.