Implant primary stability, which depends mainly on the amount and quality of bone, is important for implant survival. Socket preservation aims to reduce bone volumetric changes following tooth extraction. This animal study aims to examine whether preserving a ridge by using xenograft impairs the primary stability of the implant. Eighteen artificial bone defects were prepared in four sheep (5mmØ and 8mm length).  Defects were randomly grafted with xenografts: Bio-Oss (BO), Bioactive Bone (BB), or left for natural healing (control). After 8 weeks, bone biopsy was harvested and dental implants installed. During installation, peak insertion torque (IT) was measured by hand ratchet, and primary stability by the Osstell method. Histomorphometric analysis showed a higher percentage of new bone formation in the naturally healed defects compared to sites with xenograft (control 68.66 ± 4.5%, BB 48.75 ± 4.34%, BO 50.33 ± 4.0%). Connective tissue portion was higher in the BO and BB groups compared to control (44.25 ± 2.98%, 41 ± 6%, and 31.33 ± 4.5, p<0.05, respectively). Residual grafting material was similar in BO and BB (7 ± 2.44%, 8.66 ± 2.1 %, respectively). Mean IT and ISQ values were not statistically different among the groups. A positive correlation was found between IT and ISQ (r=0.65, p=0.00). In conclusion, previously grafted defects with xenograft did not influence primary stability and implant insertion torque in delayed implant placement. These results may be attributed to a relatively high bone fill of the defect (~50%) two months after grafting.

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