The present report describes two cases in poodle breed dogs, where both first lower molars presented dens in dente type 2, with communication between the external (oral cavity) and the root canal, with and without compromising the periodontium. Dens in dente is a malformation of teeth, probably resulting from an infolding of the dental papilla during the development of the dental germ. The etiology of dens in dente malformation is controversial, and growth pressure of the dental arch, infections, focal failure of growth of the internal enamel epithelium, trauma, and a fusion of two teeth germs have been proposed. The most commonly used classification proposed is the one of Oehlers (1957), who divided the anomalie in three forms: type 1, an enamel-lined minor form occurring within the confines of the crown not extending beyond the amelocemental junction; type 2, an enamel-lined form which invades the root but remains confined as a blind sac with or without communication with the pulp; type 3, the invagination extends through the root perforating the apex showing a "second foramen" in the apical or periodontal area without communication with the pulp. The reported cases were suspected to be dens in dente because of the alteration of the dental morphology, which was confirmed by clinical and radiographic exam. In case 1, the complications were pulpar necrosis, periapical abscess, periodontal fistula and bone resorption, while in case 2 it was found a radiolucent lysis compatible with periapical endodontic lesion and dead pulpar tissue. In case 2 it was also observed mal-positioning of the roots, presenting convergent apexes between themselves. Several methods of treatment for dens in dente have been suggested. The selection of the therapy in dogs and cats should be based on physical and radiographic exams as well as in the characteristics of the affected tooth. We chose the exodontic treatment in the case 1, where both first lower molars presented large compromising periodontium because this complication would probably lead to failure of any endodontic treatment, causing the need of a subsequent intervention. For treatment of case 2 we opted for the conventional root canal therapy (necropulpectomy), because the lateral perforation close to the furcation area, with exposition of pulpar chamber did not compromise the periodontal tissue, in a way that there was tooth mobility. In both cases the treatments were performed successfully, and was not observed any postoperative complications or recurrence.