This study examines the microbiota associated with the progression of 
experimental peri-implantitis and periodontitis induced concurrently in 
partially edentulous adult monkeys. Root-form and plate-form implants with fixed 
prosthesis in place for at least 12 months and their corresponding opposite 
molar teeth were ligated for 6 months. The microbiota in plaque around these 
ligated dental implants and molars were studied at 0, 1, 2, 3, and 6 months 
post-ligation. Plaque samples were analyzed by dark-field microscopy and 
selective and non-selective culture. Putative periodontal pathogens were 
detected as a major component of the microbiota cultured from plaque samples 
obtained from experimental peri-implantitis sites. Overall, the types and 
relative proportions of putative periodontal pathogens in plaque associated with 
ligature-induced peri-implantitis and ligature-induced periodontitis were 
similar. Only levels of anaerobic Actinomyces and spirochetes were significantly 
different between both sites. Spirochete levels were significantly higher at 
peri-implantitis sites when compared with levels at periodontitis sites after 6 
months, and spirochete levels increased significantly between 0 and 6 months 
post-ligation at implant sites. Levels of spirochetes correlated significantly 
with probing depth and bone loss at peri-implantitis sites. Overall, Actinomyces 
levels were higher at periodontitis sites. Porphyromonas species were not 
detected continuously as part of the peri-implantitis microbiota. In conclusion, 
this study finds that the microbiota associated with the progression of 
experimental peri-implantitis and periodontitis occurring concurrently in 
partially edentulous mouths are similar.