Modeling chronic periodontitis in rats: Persistent alveolar bone loss mediated by periodontal pathogens

Although widely used in periodontal research, rodents are naturally resistant to periodontitis. Conventional models, such as ligature-induced periodontitis, often fail to sustain defects due to spontaneous tissue regeneration after ligature removal. To address this, we refined a rat ligature-induced model of experimental periodontitis to better mimic the chronic, progressive nature of human periodontitis.

As a first step, following a split-mouth design, we compared the effectiveness of 3/0 silk thread and 0.008-inch orthodontic wire as ligature materials. Ligatures were applied around the left mandibular first molar for 6, 10, and 14 days. Periodontal pocket irrigation was performed every second day using a suspension of P. gingivalis, P. intermedia, and S. gordonii. As a second step, we evaluated whether silk-ligature alone, without human periopathogens, would be sufficient to induce a stable and progressive periodontal lesion. For that purpose, a silk ligature was removed on day 14, and the bone defect dynamics were monitored at 14-, 21-, and 28-days post-removal using micro-CT.

Both wire and silk ligatures, in combination with bacterial irrigation, effectively induced rapid interproximal alveolar bone loss. However, silk ligature only, without periodontopathogen colonization, resulted in significantly lower bone loss (1.076 ± 0.22 mm vs. 2.012 ± 0.374 mm; p = 0.003) and the induced alveolar bone defects gradually resolved again over time.

The proposed rat model of periodontitis is well characterized and replicates human disease by sustaining colonization with viable periopathogens, leading to progressive disease with alveolar bone loss. The suggested model is straightforward, easy to establish and can be used reliably in preclinical studies.