Objective This study was designed to evaluate the effect of surface contamination on osseointegration of dental implants surrounded by a circumferential bone defect and to compare osseointegration around Osseotite (R) with that around Nanotite (TM) implants. Materials and methods The premolars on both sides of the mandible in four beagle dogs were extracted. Following 4 months healing, two Nanotite (TM) implants and two Osseotite (R) implants were partially inserted in the left side of each mandible. Some threads protruded from the tissues into the oral cavity. Following a 5 week healing period, the implants were removed and the contaminated part of each implant was cleaned. They were then installed to the full implant length on the contra lateral side of the mandibles. The coronal 5 mm of each implant was surrounded by 1 mm circumferential bone defect. Following 12 weeks of healing period, the dogs were sacrificed and biopsies were obtained. Ground sections were prepared for histomorphometric analysis. Results All implants were associated with direct bone-to-implant contact on the portion of the implant surface contaminated previously and surrounded by bone defect. Nanotite (TM) implants performed better than Osseotite (R) implants. Conclusions The results demonstrated that implant surfaces, which were contaminated previously and were surrounded by bone defects, can osseointegrate. To cite this article:Mohamed S, Polyzois I, Renvert S, Claffey N. Effect of surface contamination on osseointegration of dental implants surrounded by circumferential bone defects.