The treatment of dental caries is called cavity filling, commonly known as dental filling. The purpose of cavity treatment is to stop the development of caries, restore the appearance of teeth, such as the reconstruction of cusps and adjacent points; achieve the restoration of tooth function; and protect the pulp tissue at the same time. The harm of cavity: If the cavity in the tooth neck is not treated in time and allowed to develop under the gum margin, the brown-black cavity will be formed, and because of its untidy and sharp edge, it will often stimulate the gum and lead to ulceration and bleeding. The cavity is one of the local causes of gum bleeding. Zou Xinming, Maxillofacial Surgery Department of Huizhou Oral Hospital The principle of cavity treatment: remove the carious lesion thoroughly and save as much hard tissue of the tooth as possible. In other words, on the basis of preventing the development of caries, remove the decayed tissue and preserve more tooth tissues. The treatment method of cavity: According to the different situation of caries, we adopt the method of grinding out the carious tissue, drug therapy, remineralization method, filling method and restoration method, etc. Clinically, the filling method is commonly used to repair the cavity defect. (1) Caries tissue grinding method: It is applicable to the teeth with extensive caries area, such as the whole occlusal surface caries and the enamel or dentin layer exfoliation, which can not be made into a filling cavity shape. Focus on grinding away the over-sharp tooth tip, tooth edge and superficial caries tissue to stop the caries from developing. (2) Drug therapy: It is applicable to the initial caries that the caries ring is shallow and no cavity has been formed yet. The drug used is silver ammonium nitrate. Adopt the ammonia silver nitrate cotton ball to rub the carious lesion tissue, usually repeatedly rubbing for 1-2 minutes, blowing with hot air, blowing dry and then repeating 1 time and blowing dry again, in order to achieve the purpose of medication for carious tissue. Because ammonia silver nitrate is a kind of antiseptic and bactericidal drug with antiseptic, astringent, bactericidal and corrosive effects. The carious tissue coated by ammoniacal silver nitrate cotton ball, generally using clove oil or 10% formalin cotton ball to produce silver-black color, and can form protein silver and reduced silver, deposited into dentin tubules, blocking dentin tubules and causing bacteria in dentin tubules to stop multiplying, and finally achieve to stop the development of caries. Drug therapy is often combined with carious tissue grinding method for better effect. The drug method is only applicable to the treatment of posterior teeth, because the ammonia silver nitrate can stain the teeth, so it is not suitable for the treatment of anterior teeth. (3) Remineralization method of carious tissue: It means that the mineralization solution of calcium, phosphorus and fluoride is artificially prepared and applied to the teeth to make the tissues of tooth lesion area mineralized, that is to say, the calcium, phosphorus and fluoride in the mineralization solution penetrate into the tooth lesion area. This process which can make the diseased area tissues re-acquire minerals is called remineralization. The method of remineralization of carious tissue is applicable to the initial caries. This is done by using artificially prepared mineralizing solution with rinses. Clinically, the use of remineralization method to treat the initial caries can reduce the chalky color or stop the development. Remineralization therapy is simple, effective, painless and safe. (4) Carious tissue filling method; it is the most common method to treat carious tissue. It is applicable to the teeth that can be made in the shape of cemented cavity after tooth decay. The filling material is fixed on the tooth by using the filling cavity shape to restore the defect and function of the tooth, in order to keep the tooth shape and maintain the integrity of the dental row.