Objectives: Although various immunological studies concerning a periapical bone resorption have been reported, the role of cytokines in the formation of periapical lesions was not clear. On the other hand, visual analysis by micro-computed tomography (μCT) was used to evaluate a periapical lesion in mouse model. In this study, we developed a new 3-dimensional (3D) evaluation method by using μCT, and investigated a role of cytokine in a periapical lesion in mice. Materials and Methods: Normal C57BL/6 mice, interferon-γ (IFN-γ) KO mice and tumor necrosis factor-α(TNF-α ) KO mice were subjected to pulp exposure and infected with Prevotella intermedia (ATCC25611) and Porphyromonas gingivalis (ATCC33277) in the mandibular first molar. A periapical lesion was determined by μCT (microfocus X-rays CT system SMX-225CT-SV3, Shimazu, Kyoto, Japan) on day 21 after infection, and 3D visual construction was performed using 3D picture quantification software. A tooth root and a periapical lesion were constructed by interpolation extraction, and the 3D images were reconstructed. The volume of the periapical lesion (a) and the volume of the tooth root (b) were measured and the ratio of bone resorption (RBR) was calculated by the following formula: RBR = (a / a + b)*100). Results: Periapical lesions were developed in mice infected with P. intermedia and P. gingivalis, and RBR was significantly increased in infected mice compared with control. However, there were no significant differences in RBR between normal mice, TNF-α KO mice, and IFN-γ KO mice. Conclusions: A new 3-dimensional (3D) evaluation method by using μCT was useful for diagnosis of periapical lesions in mice model. It was suggested that IFN-γ and TNF-α may play no role in the mechanism of bone resorption.

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