if you brush morning and evening with a paste which is non acidic and sweet properly and you do not have a gastric problem and the crowns you have gotten done have no food getting stuck in between the gums and crowns or between teeth and crowns and the root canaled teeth do not have a secondary decay or a gum problem or infections you cannot have bad breathe in your mouth . pls see a dentist to rule out the above to get to know your problem or contact me if your problem has not resolved inspite of doing so