To explore whether plaque and gingival bleeding are more frequently experienced by adolescents with juvenile idiopathic arthritis (JIA) compared to matched controls without JIA; explore whether surface- and site-specific periodontal outcomes vary between the two groups; and for participants with JIA, investigate associations between disease-specific features and periodontal outcomes. In this comparative cross-sectional study, selected surfaces, and sites of index teeth in 10–16-year-olds with JIA and matched controls were examined by modified versions of Simplified...