Fluoride is not useful for dental caries. Fluoride is generally used to prevent caries, not to treat it. This is just like the screen of our cell phone, which is already cracked, so there is no point in applying a film to the screen. Dental caries is a disease in which the hard tissues of the teeth decay and disintegrate due to bacterial infection. Once caries occurs, it means that the bacteria already exist in the hard tissues of the teeth, and will gradually proliferate, gradually making the cavity deeper and larger, and fluoride agents mainly play a role in enhancing the teeth’s ability to resist caries. Generally speaking, to treat caries, it is necessary to apply the dental power system, i.e. turbo drill, to remove the decayed part of the tooth, and then apply the filling material to fill the cavity, which is the fundamental way to treat caries.