<;P>;PROBLEM TO BE SOLVED: To provide a periodontal tissue disruption-inhibitory/ameliorative agent based on the elucidation of detailed mechanism of periodontal tissue disruption by the endotoxin of periodontal disease-causing bacteria, to provide a composition for the oral cavity containing the agent, and to provide a method for screening an active ingredient inhibiting/ameliorating the above periodontal tissue disruption. <;P>;SOLUTION: The periodontal tissue disruption-inhibitory/ameliorative agent comprises lactoferrin and one or more ingredients selected from the group consisting of evening primrose extract, allspice extract, pine tree bark extract and lecithin. <;P>;COPYRIGHT: (C)2007,JPO&INPIT