Secondary caries is a disease that occurs on the tooth after the filling has been used for a period of time. Second-ary caries is also the main reason for the replacement of dental restorations. Regardless of the material used for fillings, se-condary caries cannot be completely avoided. The proportion of secondary caries is very high after filling in permanent teeth or primary teeth. Secondary caries mainly occurs because of the formation of micro cracks after filling. When the micro crack width exceeds 50?μm, saliva will enter the micro cracks between the filling and tooth tissue. The cariogenic bacteria in the saliva will grow when the environment of micro cracks is appropriate, thereby producing secondary caries. The prevention of secondary caries includes micro crack control, fluoride use, teeth cleaning, tooth decay and gum disease treatment, and regular checkups.
