The longevity of a tooth is based not on the pulp, but on the health of the attachment apparatus. Mikroorganism and their toxic products can passed out into the periapical tissue and generates lesions of endodontic origin. The rationale of root canal treatment now is based on biologic principles. Healing will occurr if biomecanical preparation, cleaning and shaping were properly excecuted and the root canal system is hermetically sealed in three dimension.