With due respect to your assertion that your bad breath is originating in your teeth, the consensus among your periodontists that you do not have periodontitis is difficult to dismiss, and casts doubt on whether your bad breath is truly dental in origin. That is not to say that it can't be from some oral source-- for example, tooth decay can cause malodor, as well as any inflammatory condition in the mouth, such as a mucositis due to a muco-cutaneous disorder such as lichen planus, pemphigoid, candidiasis, and a plethora of others. Fixed bridgework and removable denture prostheses are common oral contributors to bad breath, as are spaces between the teeth that may harbor impacted food or other organic debris.
I would like to dismiss the possibility of upper respiratory catarrh, sinusitis, or other respiratory tract disorder, based on your prior consultations with ENT specialists. Nonetheless, these possibilities should possibly be re-explored if you believe that sufficient attention was not expended in this area.
Be advised that the warm, moist environment of the mouth, in combination with the ample supply of organic fermentable material that is often present, always creates some degree of odor, whether conspicuous or not. This inescapable fact is compounded if the normal cleansing of the mouth is impaired by diminished muscle function or diminished salivary flow, as often occurs in your age group. Commonly prescribed medications often suppress salivary production, and this may exacerbate a borderline halitosis to a degree that makes it more offensive.
Other issues may also contribute to bad breath. Some are obvious (dietary factors, such as garlic, onion, and related herbs of the allium genus, or beverages, such as coffee or tea); recreational drugs, such as tobacco
and alcohol, even certain diets, especially those that restrict carbohydrate consumption, can elicit bad breath.
Metabolic issues, such as diabetes, diminished kidney function, occult digestive tract bleeding, trimethylaminuria, and other less common disorders contribute their own unique odors. It is also becoming increasingly appreciated that gastroesophageal reflux disease is a common culprit in oral malodor.
In short, the medical exploration should be broadened if a thorough examination of your mouth proves to be unproductive. However, you may wish to have your dentist have one more look, just to rule out some of the peripheral oral issues, such as mucous membrane disorders, before you set out on another round of visits to various medical specialists.