Filling cavities should refer to repairing dental defects, and there is no such thing as the safest and strongest material to use for repairing dental defects. Nowadays, the commonly used filling materials include resin, metal and cementum. According to the specific situation of the dental defect, it is best to choose the suitable filling material. 1. Resin: It can be used for direct or indirect restoration of dental defects, and has the characteristics of good biological performance, good safety, high strength, and beautiful appearance. It is mainly used for cosmetic restoration of front teeth and restoration of one or two types of cavities in back teeth. 2. Metal: commonly used in the clinic is silver amalgam, which is a material with a long history of use. It has good compressive strength and plasticity. But because of its color is silver-gray, so it is mostly used for filling of dental defects in posterior teeth. It is rarely used because it is easy to stain the dentin. 3. Water portal type: clinically seen phosphate water portal, glass ionomer water portal, etc., mainly used for deep caries cushioning, pulp protection or temporary filling of carious cavities. Dental defects should be timely medical care, improve the examination, standardized treatment under the guidance of a professional physician.