Oral Health, Saliva Bacteria, and Disease Activity in Children With JIA: A Cross-Sectional Study.

Inclusion Criteria: * Children aged 6 to 16 years. * Diagnosed with juvenile idiopathic arthritis according to the International League of Associations for Rheumatology (ILAR) classification criteria, excluding the systemic-onset subtype. * For the active disease subgroup, all of the following must be met: 1. Presence of active arthritis as determined by the attending rheumatologist; 2. Planned initiation or adjustment of disease-modifying antirheumatic drugs (DMARDs) or biologic agents within 1 month after enrolment; 3. Meeting the following disease activity criterion: JADAS-27 score \> 1. For the remission subgroup, the following must be met: JADAS-27 score ≤ 1 and clinically stable disease. * Able to cooperate with oral examination and saliva sample collection. * Written informed consent provided by a legal guardian, with assent obtained from the child. Exclusion Criteria: * Use of systemic antibiotics within 3 months prior to enrolment, or use of mouthwash containing antibiotics, corticosteroids, or chlorhexidine within 1 month prior to enrolment. * Diagnosis of other autoimmune diseases (e.g., systemic lupus erythematosus, Sjögren's syndrome), chronic inflammatory diseases (e.g., inflammatory bowel disease), diabetes mellitus, congenital heart disease, or other systemic conditions that may affect the study outcomes. * Presence of acute infection at the time of sampling or examination (e.g., body temperature \> 37.5°C, upper respiratory tract infection, acute oral infection). * Significant cognitive or behavioural impairment that prevents cooperation with study procedures. * Ongoing or planned orthodontic treatment within the next 6 months.