Microbiologic characterization of ligature-induced peri-implantitis in the microswine model

The purpose of this study was to evaluate the microbiologic changes associated with induction of peri-implantitis in the microswine. A split-mouth design was utilized. Three implants were placed in the edentulous mandibular bicuspid region of 2 microswine yielding 12 implants for evaluation. The experimental implant abutments were ligated with 4-0 silk suture material to induce peri-implantitis for a period of 45 days. The control implant abutments were not ligated. The control implants were scaled and cleaned at each time interval using plastic scalers. The attachment level (AL), probing depth (PD), gingival index (GI), and plaque index (PI) were measured at day 0 (baseline) and days 14 and 45. Microbiologic samples were taken from the "sulcus" with paper points at each interval and were dispersed in prereduced media; plated on selective and non-selective media; and grown under aerobic, anaerobic, and capnophilic atmospheres. A greater AL, increased PD, and higher GI and PI scores were noted among the experimental implants. The controls remained essentially unchanged. Radiographs revealed that experimental implants showed an increased amount of bone loss when compared to control. Bone loss caused the implant threads to be exposed in the experimental implants. Microbiologic studies revealed that there was a shift from Gram-positive facultative organisms to Gram-negative obligate anaerobes, including black pigmented Bacteroides, in experimental implants. The microbiota of the control implants remained primarily Gram-positive facultative organisms. The microswine appears to be a suitable animal model for evaluation of osseointegrated implants. Importantly, under the experimental conditions reported, osseointegrated implants were susceptible to "periodontal" breakdown or peri-implantitis.