How do i know if i still have some cavities left after treatment?

Pain to sweets: Slowly building pain to sweets is an indication of caries (tooth decay).

Sometimes none: Carious lesions don't always have outward signs.. Many patients are not even aware that they have cavities. A trained eye and experience reading radiographs, as well as a thorough examination should catch your lesions. Large old fillings sometimes mask recurrent decay. Pain to cold and sweets are indicative of a cavity or leakage of an old filling.

One more comment: Dr. Davantzis already gave you a thorough and excellent answer. I have to assume that you have discussed this with your own dentist who is treating you. If not, you should. You should trust the dentist who is treating you for accurate answers to your questions. Otherwise, consider finding one by recommendations whom you do. If you still have suspicions, perhaps they are unwarranted concerns.