hello thanks for consulting at hcm..lot of causes are there for metallic breath,,namely oral problems -bacteria may result in metallic breath,, others include jaundice, metal poisoning, heartburn, other stomach related problems, pregnancy, and intake of drugs..you could use strong mint flavored chewing gum or certain other flavored confectionaries, Cinnamon, cloves or lemon are very efficient in providing temporary relief.however do consult a internal medicine specialist for a check up and treatment if problem persists..since you have ruled out dental problem, u have also gone to ge specialist too, to check problem in the sinuses if any, you have to consult a ent specailist,,hope it helps,,take care,,