title: The natural history of periodontal disease in man. Study design and baseline data.
mesh_terms: D000293:Adolescent; D000328:Adult; D004522:Educational Status; D006801:Humans; D008297:Male; D009664:Norway; D010510:Periodontal Diseases / Q000453:epidemiology* / Q000209:etiology; D044469:Racial Groups; D012959:Socioeconomic Factors; D013188:Sri Lanka; D013997:Time Factors