According to statistics, 80% ~ 90% of bad breath comes from the mouth. Untreated dental caries, residual roots, residual crowns, poor repair, abnormal anatomical structure, gingivitis, periodontitis, oral mucosal diseases and so on can all cause bad breath.
Dental caries and periodontal disease are the most common related diseases. Food residue and plaque are often left in the cavity of deep caries and under the overhang of bad restorations. Bacteria: odor is produced after fermentation and decomposition. Pulp necrosis or suppurative pulpitis, if not treated, will also give off a bad smell.
Looking for reasons:
Bad breath is not terrible, as long as the cause is found, it can be treated. First of all, consider whether bad breath is oral or non-oral, and we can't rule out the factors related to bad breath, such as respiratory diseases (infection and necrosis of nasal cavity, maxillary sinus, pharynx and lungs).
Diseases of digestive system (gastritis, gastric ulcer, duodenal ulcer, gastrointestinal metabolic disorder, constipation, etc. ), substantial organ damage (liver failure, renal failure) and diabetic ketosis, uremia, leukemia, vitamin deficiency, etc. These diseases should be treated locally or systematically first.