1. Objective. The aim of this study was to investigate whether dental implant exposure to the maxillary sinus cavity increases the risk of maxillary sinus complications. 2. Study design. An implant was placed bilaterally in the maxillary sinus of eight adult female mongrel dogs in a way that it penetrated the bone and mucous membrane of the maxillary sinus floor to the extent of 2 mm, 4 mm, or 8 mm. The implants were left in place for six months. 3. Results. Radiographic and histologic examinations did not show any signs of pathologic findings in the maxillary sinus of the eight dogs. 4. Conclusion. This study indicates that implant protrusion into the maxillary sinus cavity is not related to the development of sinus complications.