ABSTRACT: The sinus membrane perforationcombined withexposing dental implant into the maxillary sinus is considered as a potential risk factor for implant failure and sinus complication.The present studyinvestigated the incidence of intentional sinus membrane perforation by dental implant in different depths and the possible risk factors associated with membrane perforations and assessed the implant osseointegratin and the survival rate of implants placed in the posterior maxillain a dog model. A total of 32 titanium implants were placed in the bilateral maxillary first molar areas of 16 adult mongrel dogs with different penetrating depths of implants into the maxillary sinus cavities (group A: 0 mm; group B: 1 mm; group C: 2mm; group D: 3 mm). The sample, block biopsies were harvested six months after surgery and evaluated by Biomechanical analysisandradiographic observation.After six months healing period, no signs of inflammatory reactions or complications were observed in any maxillary sinus of the sixteen doges. The results showed that the posterior maxillary edentulous areas with reduced bone height may be successfully rehabilitated with implants that penetrate the Schneiderian membrane and extended into the maxillary antrum. During the 6-monthes observational period in canines, despite the different protrusion extent, penetration of dental implant into the maxillary sinus with membrane perforation did not compromise the dental implant osseointegation processes and the sinus health. It was also found out when penetrating depth into the sinus is less than 2 mm, the apical portion of implant could be re-covered by regenerating membrane.No significant differences were found among groups regarding implant stability, bone-to-implant contact (BIG) and bone area in the implant threads (BA). In conclusion, invading the maxillary sinus by dental implant is not necessarily associated with significant complications as was generally expected, and stable osseointegrated dental implant that perforate the sinus without apparent immediate complication cannot be considered a harmful factors that necessitate its immediate removal, so could be left provided that they were initially stable.