Dental researcher: Filling a cavity in a tooth is not a harmless procedure: it inevitably damages some of the healthy parts of the tooth  Cavities are harmful only if the decay reaches the nerves inside the tooth, and many cavities, if left untreated, never progress to that point
Ttherefore, dentists should not fill a cavity unless the nerves inside the tooth are in imminent danger from that cavity
Dentists should help their patients to prevent cavities rather than waiting until cavities are present to begin treatment.