Salivary Mitofusin-1 Levels in Periodontitis: Associations With Disease Severity, Smoking, and Treatment Response

Inclusion Criteria: * Willing and able to provide written informed consent. * Systemically healthy (no history of diabetes mellitus, immunodeficiency, malignancy, or other systemic conditions that could affect periodontal status). * Have a minimum of 20 natural teeth (excluding third molars). * No antibiotic therapy or periodontal treatment in the last 6 months. For Healthy Control Group: No clinical attachment loss. Probing depth ≤ 3 mm. No radiographic evidence of bone loss. Low gingival and plaque index scores. For Mild Periodontitis Group: Diagnosed with Stage I or II periodontitis according to the 2018 AAP/EFP classification. Clinical attachment loss of 1-4 mm. Radiographic bone loss of ≤15-33%. Non-smoker. For Severe Periodontitis Group: Diagnosed with Stage III or IV periodontitis according to the 2018 AAP/EFP classification. Clinical attachment loss ≥ 5 mm. Radiographic bone loss to the mid-advanced level of the root. Non-smoker. For Severe Periodontitis with Smoking Group: Meets all criteria for the Severe Periodontitis Group. Regular smoker (at least 10 cigarettes per day for a minimum of 5 years). Exclusion Criteria: * Fewer than 20 natural teeth (excluding third molars). * Presence of any systemic disease (e.g., diabetes mellitus, immunological disorders, cancer). * Use of antibiotics or receiving periodontal treatment in the last 6 months. * Pregnancy or lactation. * For non-periodontitis groups (Healthy Control): Any signs of periodontitis. * For periodontitis groups (all): History of smoking cessation for at least 5 years (must be either a current regular smoker or a never-smoker, depending on the group definition).