The aim of the present study was to evaluate the impact of the quality of the coronal restoration and of the root filling on periapical health. In a sample of 937 root filled teeth which had not received restorative treatment in the previous year, the technical quality of the coronal restorations and of the root fillings was radiographically scored; in addition the technical quality of the coronal restorations was clinically scored as well. The data showed that the technical standard of both coronal restoration and root filling were essential to periapical health. The study also showed the relatively limited value of epidemiologic findings. Epidemiologic research is descriptive as well as analytical in approach. According to the present data, endodontic failure cannot be fully explained by radiographic analysis only. Nevertheless, epidemiologic data remain a valuable component to the source of knowledge regarding etiologic factors and proper treatment procedures in order to improve the results of endodontic practice.