2007 Volume 50 Issue 1 Pages 80-90
The exact mechanism of periradicular cystogenesis is not well understood. The purpose of this study was to evaluate histopathologically extensive proliferation of epithelial rests of Malassez in the periodontal ligament and initial periradicular cyst formation with central cavity induced by apical overinstrumentation and overfilling. Thirty-two root canals of thirty-two sound permanent teeth (24 upper and lower anterior teeth, and 8 upper premolars) in four crab-eating (Macaca irus) adult monkeys were prepared for this experiment. Pulp extirpation procedures were performed under general and local anesthesia, with a tooth by a rubber dam in all teeth. The root canal length was determined by using an electronic device (Root canal meter, Onuki). The root canals of most teeth were prepared on the apex. The canals were irrigated several times alternately with 6% sodium hypochlorite and 3% hydrogen peroxide. The canal treatment after the pulp extirpation was as follows. Treatment Group 1: canal instrumented at the apex Group 2: canal instrumented and filled short of the apex Group 3: canal instrumented and filled beyond the apex Most canals were filled with lateral condensation of gutta percha points and zinc oxide eugenol sealers (Canals®, Showa Yakuhin Kako). In half of the cases, the teeth were overfilled with sealers about 1 to 2 mm beyond the apex. In some canals, a sterile dry cotton pledget or moistened cotton pledget with PTC was placed. In other canals the dentinal chips were plugged slightly beyond the apex. All the cavities were carefully lined with zinc phosphate cement and then sealed with amalgam. All test teeth were radiographed. After the experimental period from 1 to 4 weeks, the animals were sacrificed. The teeth were fixed in 10% neutral formalin. After decalcification, serial celloisin sections, 10 to 15μm thick, were prepared and stained with hematoxylin-eosin, Schmol stain and Masson Goldner stain for light microscope observation. The results were as follows: 1. Generally, it was found that a periapical inflammatory response occurred in all teeth of the overinstrumented and overfilled groups. 2. Four weeks following completion of the canal fillings, an area of chronic inflammation was noted far beyond the apex. In the periodontal ligament and in the bone marrow around the apex, small masses of proliferated epithelium were present. 3. Initial developmental stage of periradicular cyst was confirmed by 4-week specimens in the group of overfilled canals.
