A study of periapical overfilling in root canal treatment in the molar of rat

Abstract

One hundred and nine overfilled root canals of the mesial root of first mandibular molars of rats, using a variety of materials, were studied histologically. Evidence was found that, when the overfilling root canal material was hard and compact, the surrounding tissues tended to encapsulate it. However, a zone of loose connective tissue containing many macrophages frequently formed between the capsule and the filling material. When the material was not so compact, it was found dispersed in the sections and was resorbed more rapidly. Detritus, caused by instrumentation, was often projected beyond the foramen and was dispersed in the periapical tissues. Where the excess of material entirely filled the periapical space there was necrosis of the bone. Resorption of necrotic bone and of the overfilling material occurred, both from the periodontal ligament and from the adjacent red bone marrow. Root canal material in contact with bone marrow became encapsulated more slowly than that in contact with periodontal ligament, and resorption was slower. Material in relation to the mandibular canal showed a poorly differentiated fibrous capsule. When resorption of the root left the overfilling material in direct contact with periodontal membrane, tissue reaction varied according to the nature of the material. Zinc oxide and eugenol induced a mild inflammatory reaction and was resorbed very slowly. Fillings of a resorbable paste provoked a more intense polymorphonuclear leucocyte infiltration and were rapidly resorbed.