BACKGROUND New filling biomaterials with better physicochemical properties would create a favorable biologic environment for the healing of periapical tissues. The aim of this study was to evaluate periapical repair after biomechanical preparation and root filling with an adhesive system compared with the gold standard material (gutta-percha+sealer) in dog teeth. METHODS The pulp of 25 root canals was removed. The apical cementum layer was perforated, and the root canals were prepared up to size #60 K-file followed by step-back shaping with the #90 K-file and filled by the lateral condensation technique. In the experimental group (n=15), the Resilon System (Pentron Clinical Technologies, Wallingford, CT) was used. As a control material (n=10), gutta-percha cones and pulp canal sealer were used. After 60 days, the animals were killed, and 10 histologic parameters were evaluated. Differences among the groups were analyzed by using the Mann-Whitney and Fisher exact tests. RESULTS In radiographic and histologic evaluations, most fillings were slightly short of the apex. Progressive regenerative stages were observed; however, there was a reduced prevalence of biologic foraminal closure. No significant differences were observed between the 2 biomaterials with regard to any of the parameters evaluated (P>.05). CONCLUSIONS The Resilon System shows periapical biocompatibility equivalent to the gold standard material.