Bad breath may be caused by systemic, non-oral conditions. These include sinusitis, tonsilloliths (small calcified matter in the tonsils), kidney failure, liver disease etc. In this cases, it is time to consult an internist.
The tiny crevices in between teeth and gums,faulty dental work, the teeth themselves, abscesses (pus-filled, inflamed areas around the teeth) and unclean dentures also harbor halitosis-causing bacteria, although to a much lesser degree than the tongue.