In the model of periodontitis induced by oral pseudomonas gingivalis in mice, 4-phenylbutyric acid (4-PBA, an ER stress inhibitor) reversed the significant expression of BIP, XBP1, total XBP1, CTSK, and TRAP genes and the increase in the osteoclast number and bone resorption in alveolar bone. The gene discussed is XBP1; the disease is periodontitis.