Lutfi M.Elhamruni^A; HamdyAbdelmegeed M.Marzook^B; Wael Mohamed S. Ahmed^C; Mohamed Abdul Rahman Mohamed ^D A-   MD, Candidate, Oral & Maxillofacial Surgery, Faculty of Dentistry, Mansoura University, Mansoura, Egypt. B-   Associate Professor of Oral & Maxillofacial Surgery, Faculty of Dentistry, Mansoura University, Mansoura Egypt. C-   Assistant Professor of Oral & Maxillofacial Surgery, Faculty of Dentistry, Mansoura University, Mansoura Egypt. D-   Associate Professor of Oral biology, Faculty of Dentistry, Mansoura University, Mansoura Egypt. Abstract: Objective:The purpose of this study was to investigate the effect of the dental implant penetration into the maxillary sinus cavity in different depths on osseointegration and sinus health in a dog model. Materials & methods: the study sample included eight titanium dental implant placed in four female dogs immediately after extraction of first maxillary molar in the palatal socket, and assigned into four groups according to the protruding of implant tips (Control group A= 0 mm), (Study groups B,C and D with protrusion of 1,2 and 3 mm respectively). The bone blocks of the implants were harvested five months post-operatively and evaluated by CBCT and histological analysis. Results: The whole groups showed no signs of inflammation during the five months period of the study. The tips of the implants in group B with penetrating depths of 1 mm were found to be fully covered with newly formed bone. The tips of the implants in group C with penetrating depths of 2 mm were exposed in the sinus cavity and showed partially new bone coverage, while depths of 3 mm group D were found no bone formation and the dental implant fixture sites were communicated with the sinus cavity. No significant differences were found among groups regarding implant stability. Conclusion: Despite the protrusion extents, penetration of dental implant into the maxillary sinus with membrane perforation does not compromise the sinus health and the implant in canine.