Changes in Peri‐Implant Tissues Subjected to Orthodontic Forces and Ligature Breakdown in Monkeys

The aims of this investigation were to histologically evaluate in monkeys the effect of a repetitive mechanical trauma alone on the peri‐implant tissues, and the effect of a repetitive mechanical trauma in combination with hgature‐induced peri‐implantitis on the peri‐implant tissues. The study used 5 male cynomolgus monkeys. Prior to the start of the study, all premolare and the first and second molars in the mandible were extracted. After a heahng period of 12 weeks, following tooth extraction, split/full thickness flaps were elevated on both sides of the mandible in order to expose the bony ridge. Four implants, of 3.75 mm in diameter and 7 mm in length, were then inserted on each side and the flaps were readapted and sutured in place. Following a heahng period of 16 weeks, the second stage procedure was performed, impressions were taken, and custommade crowns using a non‐precious metal alloy were fabricated and inserted on all implants 4 weeks after abutment connection. At the same time peri‐implantitis was induced on one side of the mandible by placing plaque‐retentive ligatures around the implants. On the other side, an oral hygiene program consisting of thrice weekly bmshing with a toothbrush and flour of pumice mixed with 2% Chlorhexidine was initiated. Four months later, a repetitive mechanical trauma was initiated on implants 1 and 2 on both sides in the mandible. Consequently, a split mouth design was obtained: 1) test 1 = hgature‐induced peri‐implantitis alone (LPNO); 2) test 2 = ligature‐induced peri‐implantitits with a repetitive mechanical trauma (LPMT); 3) test 3 = healthy peri‐implant tissues with a repetitive mechanical trauma (MT); and 4) control (NO) = healthy peri‐implant tissues with no repetitive mechanical trauma. Following 16 weeks of repetitive mechanical trauma the animals were sacrificed. Histologic observations and computed‐assisted histometric and histomorphometric analyses were performed to determine the amount of peri‐implant bone loss and the percentage of direct mineralized bone‐to‐implant contact around each endosseous oral implant. Histologically, all implants yielded osseointegration at the light microscopic level. There was a significant difference regarding the mean direct mineralized bone‐to‐implant contact length as a fraction of the total implant length between the healthy (i.e., MT and NO) and diseased sites (i.e., LPNO and LPMT) (P < 0.05). When comparing the percent of direct mineralized bone‐to‐implant contact f