Time course of morphologic changes in periodontal tissue was studied in 42 miniature pigs with experimental bruxism. An inflammation has developed in the marginal periodontium. At first the inflammatory infiltrate was situated under the epithelial fixation to the tooth involving destruction of the epithelial fixation and formation of pockets, inflammatory infiltrate, and granulation tissue, these destructive changes involving the lower sections of the periodontium. Signs of resorption were detectable in the dental alveolus osseous wall, cement, and dentin. The changes in the periodontal tissue described above appear to result from a complex of factors developing in experimental animals with simulated bruxism.