Time-course and risk analyses of the development and healing of chronic apical periodontitis in man.

Roots with and without preoperative chronic apical periodontitis were root canal treated and followed clinically and radiographically yearly for up to 4 years. Of 732 roots treated, 599 (82%) were available for evaluation at one or several recalls. Chronic apical periodontitis (CAP) was recorded with the periapical index scoring system. CAP developed in 29 of 473 (6%) of teeth without preoperative signs of disease, whereas 111 of 126 (88%) initially diseased roots showed signs of healing. The rate of healing CAP and the rate of emerging CAP were calculated, and analyses of event occurrence each year of observation were performed. Peak incidence of healing or emerging CAP was at 1 year in both instances. Risk assessments at 2, 3, and 4 years did not indicate an added risk of filled roots developing CAP during this period. Complete healing of preoperative CAP in some instances required 4 years for completion, while signs of initiated, but incomplete, healing were visible in at least 89% of all healing roots after 1 year. Risk analyses may provide relevant information in addition to or in substitution for success/failure analyses.