Purpose: Peri-implantitis is a challenging situation that leads to tissue destruction and eventual implant failure. The purpose of this study was to evaluate and compare, clinically and histologically, the influence of ligature-induced peri-implantitis on two implant designs in a canine extraction socket model. Materials and Methods: Sixty-four implants (4.1 × 13 mm) were placed bilaterally in eight dogs immediately after extraction of the mandibular premolars (P3, P4) and molars (M1, M2). Thirty-two conventional threaded implants (group A) and 32 tantalum-based porous implants (group B) were placed. After 12 weeks of normal healing, experimental peri-implantitis was induced in four dogs via the placement of ligatures subgingivally around the implant necks in the treatment group; the control group remained ligature-free. Two dogs in each group were euthanized after 12 or 26 weeks of plaque accumulation (control group dogs received regular cleanings). Clinical evaluations were conducted during the observation period and histologic sections were obtained for histologic and histomorphometric assessments. Results: All the implants exhibited clinical and histologic osseointegration. The treatment group showed significant loss of peri-implant tissue from the induced peri-implantitis. Pocket probing depths for the treatment groups were significantly greater than those of the control groups. Mean bone-to-implant-contact values were not statistically different for control vs treatment groups or for group A vs group B. In the treatment group, group B implants exhibited mean bone ingrowth of 28.4% to 36.3% and achieved more bone formation along the length of the implant than group A implants in the treatment group. Conclusion: Implant design did not influence the tissue response or histomorphometric findings under induced peri-implantitis in the canine extraction socket. Keywords: bone ingrowth, peri-implantitis, porous tantalum