Abstract
8 years after a root canal treatment at our clinic a sizable periapical lesion was found along with abnormally large root canal and root apex. In fact root canal was so wide that conventional gutta-percha filling material could not be applied. As such biocompatible filling material, Pro Root MTA, which chemically bonds to the root canal walls, was employed. The lesion has regressed, and the post-treatment course has been stable.