Background: Bone density, an important factor in functional bone quality, can affect the success of implant osteointegration or orthodontic treatment. A number of studies report that chonic periodontitis constitutes one risk factor of osteoporosis characterized by low bone mineral density and that the mandible is susceptible to osteoporosis. Purpose: The purpose of this study was to evaluate mandibular bone density in animal subjects suffering from chronic periodontitis. Methods: 40 male Wistar rats were divided into four chronic periodontitis groups and four control groups (each group n=5). As chronic periodontitis models, the subjects were injected with 2×109 CFU/ml of Porphyromonas gingivalis in the sulcular gingiva, whereas control group members were injected with normal saline. After 2, 3, 4 and 6-week injection periods, the subjects were sacrificed and radiographic examination of the mandibular bone subsequently performed. Mandibular bone density was evaluated by histometric analysis. Results: The mandibular bone density in members of the chronic periodontitis group was significantly lower than those of the control group (p<0.05). The reduced mandibular bone density in the chronic periodontitis group was in line with the protracted bouts of periodontitis. Conclusion: Reduced mandibular bone density was found in the chronic periodontitis model. The longer the duration of a bout of chronic periodontitis, the greater the reduction in mandibular bone density.

Background: High-mobility group box 1 (HMGB1) was suggested to be associated with the pathogenesis of chronic periodontitis which characterized by alveolar bone loss. HMGB1 was defined as a bone-active cytokine, but the rule of HMGB1 in bone loss of chronic periodontitis is still understood. Aim: The aim of this study is to investigate the expression of HMGB1 on osteoblasts and osteoclasts in the mandible of chronic periodontitis. Methods: This experimental study was conducted to rats injected by Porphyromonas gingivalis into the buccal and lingual subgingival area at a concentration of 2 × 109 CFU/mL three times a week with 2-day apart for 2, 3, 4, and 6 weeks as chronic periodontitis group and injected by normal saline as control group. Analysis of variance was used to examine the differences between groups followed by least significant difference post hoc test with the level of significance was <0.05. Results: The HMGB1 expression was found in both osteoclasts and osteoblasts of mandibular bone by immunohistochemistry analysis. There was a difference of HMGB1 expression on osteoblasts and osteoclasts of chronic periodontitis. HMGB1 expression was found increased significantly in mandibular osteoblasts of chronic periodontitis, whereas the HMGB1 expression in mandibular osteoclast is higher in 2 and 3 weeks, but it was lower in 4 and 6 weeks. Conclusions: This study indicated a potential role for HMGB1 in bone loss of chronic periodontitis. HMGB1 on mandibular osteoclasts and osteoblasts may play different rules in the onset and progression of chronic periodontitis.