Salivary Melatonin and MMP-9 Levels in Stage III Periodontitis: A Pilot Study Using Standardized Pre-Sleep Saliva Collection

Background and Objectives: Periodontitis is a chronic multifactorial inflammatory disease characterized by progressive destruction of the tooth-supporting tissues. Although periodontal diagnosis is primarily based on clinical and radiographic parameters, salivary biomarkers may provide additional biological information on inflammatory activity and host-response regulation. Matrix metalloproteinase-9 (MMP-9) is involved in extracellular matrix degradation and periodontal tissue destruction, whereas melatonin is a circadian-related molecule with antioxidant, anti-inflammatory, and immunomodulatory properties. However, evidence regarding the simultaneous assessment of salivary MMP-9 and melatonin using standardized pre-sleep saliva collection remains limited. This pilot study aimed to evaluate salivary melatonin and MMP-9 concentrations in periodontal health and stage III periodontitis, to assess their interrelationship, and to explore their preliminary in-sample ability to distinguish periodontal health from stage III periodontitis. Materials and Methods: This cross-sectional pilot study included 18 systemically healthy non-smoking adults: 9 periodontally healthy participants and 9 patients with stage III periodontitis. Pre-sleep unstimulated saliva was collected between 23:00 and 24:00 h or immediately before sleep, following a standardized protocol. Salivary MMP-9 and melatonin concentrations were determined using enzyme-linked immunosorbent assay. Periodontal diagnosis was established according to the 2017 World Workshop classification. Group comparisons, correlation analyses, and receiver operating characteristic curve analyses were performed as exploratory analyses. Results: Salivary melatonin concentrations were significantly lower in patients with stage III periodontitis than in periodontally healthy participants (p = 0.019), with a large effect size (Hedges’ g = 1.261). Salivary MMP-9 concentrations were higher in the periodontitis group, but the difference was not statistically significant (p = 0.465). No significant correlation was found between salivary melatonin and MMP-9 levels. Receiver operating characteristic analysis suggested preliminary in-sample discriminatory ability for melatonin (AUC = 0.827; p = 0.019), whereas MMP-9 showed limited and non-significant discriminatory ability (AUC = 0.593; p = 0.508). Conclusions: In this pilot sample, lower pre-sleep salivary melatonin levels were associated with stage III periodontitis, whereas MMP-9 showed limited standalone discriminatory ability. These findings should be interpreted as preliminary and hypothesis-generating. The present study does not establish a clinically applicable diagnostic cut-off or validated diagnostic utility for salivary melatonin. Larger, independently validated studies are needed to confirm these observations.