Secondary caries is the lead cause of filling replacement. It is a caries lesion that appears near the edge of existing restoration and includes “outer lesion”, a newly formed primary caries and “wall lesion”, a process that appears between the filling and the cavity wall. This paper shows the process of formation, characteristics, and prevention of secondary caries. The formation of secondary caries is influenced by the same etiological factors as in primary caries formation (such as nutrition, oral hygiene, patient’s salivary activity), with a microfracture that is characteristic of secondary caries. Many researchers have has shown that the material, the class and fluoride occurrence in fillings as well individual’s risk of caries formation all have an influence on the frequency of secondary caries. Restorative dentistry is focusing more and more on less invasive approaches to treating secondary caries where the main goal is preserving the patient's natural dental structure. Secondary caries treatment demands the removal of the filling and removal of the parts of the tooth affected by the caries which results in weakened tooth structure and can have serious consequences. The focus has been shifted more and more to secondary caries prevention, with both the dentists and the patients being an important part of this process which includes maintaining good oral hygiene and using antiseptics. There are many different methods of secondary caries prevention such as cavity disinfection or tooth restoration using the filling with fluorides or antimicrobial agent. This paper presents general information on secondary caries prevention methods and their effectiveness supported by research.