60 patients have been selected from a group of 490 patients, who had a full mouth radiographic status taken in connection with a population study of apical periodontitis in Aarhus Community. The selection criteria for the 60 patients were patients with a persisting apical periodontitis, Periapical Index (PAI) score 3-5, on front teeth and premolars in the upper jaw. The orthograde root filling in the tooth must be at least 2 years old and sufficient regarding density and length.