The common clinical causes of smelly teeth are dental caries, gingivitis or periodontitis, and poor living habits. 1. Dental caries: this condition refers to a disease of progressive destruction of dental hard tissues under the joint action of bacteria, host, diet and time. Food debris due to long-term embedded in the caries cavity, under the action of bacteria will gradually produce volatile sulfur compounds, such as hydrogen sulfide, dimethyl sulfide, methyl mercaptan, etc., will make the teeth stink. 2. Gingivitis or periodontitis: inflammation of the gums or periodontium, which will stimulate the bacteria in which a large number of reproduction, bacterial metabolism will produce a large number of indole, hydrogen sulfide and other irritating gases, resulting in tooth odor. 3. Poor living habits: some people like to eat onions, garlic and other foods with an irritating odor, the residue of which adheres to the teeth can also cause tooth odor. There are also smokers who smoke cigarettes after combustion of chemical compounds will adhere to the surface of the teeth, resulting in odor, but also on the respiratory tract to cause damage. If there are relevant disease factors, it is recommended to go to the hospital stomatology department for treatment; if it is a common habit problem, it is recommended to adjust personal habits.