Increased swelling and osteoclast numbers in mice with Porphyromonas gingivalis oral infection. Paws measured in the medial–lateral and dorsal–ventral dimensions at timeline days D65, D67, D70, and D72 (35, 37, 40, and 42 days after complete Freund’s adjuvant (CFA)/collagen II (CII) immunization) were compared with (A) paws with visual assessment score of 0 (no arthritis) and (B) paws that developed a visual assessment score of 4. (C) Representative figures of hind paws that developed score 0 (upper panel), score 4 with medial–lateral measurement of 4 mm in mice from the CFA/CII group (middle panel), and score 4 with medial–lateral measurements of 5.0 mm and 5.5 mm in mice from the P. gingivalis (Pg)-CFA/CII group (lower panel). Error bars represent ± standard error of the mean (SEM) of four to six mice per group, P <0.05, linear regression analysis. (D) No differences between groups were observed in paws evaluated by micro-computed tomography for periosteal new bone and cortical bone destruction bone area; however, the osteoclast number by tartrate-resistant acid phosphatase (TRAP)-positive staining was significantly increased in mice with oral P. gingivalis. Error bars represent ± SEM of four to six mice per group, P <0.05, Student’s t test.