Induction of experimental periodontitis in nice with Porphyromonas gingivalis adhered ligatures

Background: Little information is available on the colonization of periodon topathic bacteria and alveolar bone loss in a mouse system, because of the difficulty in establishing bacteria in the oral cavity. The aim of this stu dy was to establish experimental periodontitis in mice by applying a Porphy romonas gingivalis-adhered ligature onto the molars. Methods: Specific pathogen-free C3H/HeN mice were divided into 3 groups: 80 infected, 80 sham-infected, and 48 non-treated control mice. Sterile silk ligatures were preincubated with and without P. gingivalis 381 in vitro and then physically tied on the right maxillary first molar of infected and sh am-infected mice, respectively. Ten mice from the infected and sham-infecte d groups and 6 from the control group were sacrificed at 2-week intervals f or up to 15 weeks after infection. Results: Plaque samples were collected at the time of sacrifice and alveola r bone loss was examined. The results indicated that P. gingivalis was reco vered from the plaque samples in 95% of the infected mice after 1 week and then gradually dropped to 58% after 15 weeks of infection, whereas P. gingi valis was not isolated in either sham-infected or control mice throughout t he experimental period. The infected mice showed significant P. gingivalis- induced bone loss at the sites where the ligature was tied weeks 13 to 15. A linear regression analysis revealed a significant positive correlation be tween the number of P. gingivalis recovered and alveolar bone loss at 15 we eks after infection (P <0.01). Conclusions: The use of a P. gingivalis-adhered ligature supported a long-l asting infection of P. gingivalis in mice, resulting in P. gingivalis-induc ed alveolar bone breakdown.