Salivary Dysfunction in Primary and Secondary Sjögren’s Syndrome: Functional Assessment and the Exploratory Role of Salivary Microcrystallization

Background: Salivary gland dysfunction is a central manifestation of Sjögren’s syndrome, but the relationship between quantitative salivary impairment and salivary microcrystallization remains insufficiently defined. This study aimed to assess unstimulated and stimulated whole salivary flow and salivary pH in patients with primary and secondary Sjögren’s syndrome and to explore salivary microcrystallization indices as complementary descriptive markers of salivary physicochemical patterns. Materials and Methods: This cross-sectional observational study included 126 patients diagnosed with primary or secondary Sjögren’s syndrome. Unstimulated whole salivary flow, stimulated whole salivary flow, and salivary pH were assessed under standardized conditions. Salivary dysfunction severity was classified according to predefined functional salivary parameters. Salivary microcrystallization was evaluated microscopically on dried saliva samples and expressed using the IMK-RFR and IMK-RFS indices. Differences between disease subtypes and associations between salivary parameters, microcrystallization indices, and dysfunction severity were analyzed. Results: The mean unstimulated salivary flow rate was 0.272 ± 0.246 mL/min, while the mean stimulated salivary flow rate was 1.04 ± 0.50 mL/min. In unadjusted analyses, patients with primary Sjögren’s syndrome showed lower unstimulated and stimulated salivary flow rates than patients with secondary Sjögren’s syndrome. Both salivary flow parameters were inversely associated with salivary dysfunction severity. In an exploratory internal consistency ROC analysis, unstimulated salivary flow showed good internal agreement with grade ≥ 3 salivary dysfunction, while stimulated salivary flow showed very high internal agreement. Salivary pH showed limited internal consistency with dysfunction severity. Firth penalized logistic regression indicated that stimulated whole salivary flow remained associated with grade ≥ 3 salivary dysfunction after adjustment for unstimulated salivary flow. IMK values described salivary microcrystallization patterns within the Sjögren’s syndrome cohort; however, they were not robustly correlated with salivary flow, pH, or dysfunction severity. Conclusions: Salivary flow assessment remains a simple, non-invasive, and clinically relevant method for evaluating glandular dysfunction in Sjögren’s syndrome. In this cohort, primary Sjögren’s syndrome was associated with lower salivary flow rates, but these unadjusted findings should be interpreted as descriptive. Salivary microcrystallization provided exploratory information on qualitative salivary patterns, but its clinical value remains limited and requires methodological standardization and validation in larger prospective studies.