Maria Ovsepyan

Background: Sialolithiasis is a multifactorial biomineralization disorder in which local salivary, biological, and potentially environmental factors may influence stone formation and maturation. The relationship between drinking-water mineralization and the chemical composition of salivary stones remains poorly understood. This study aimed to characterize the composition of sialoliths in an Armenian population and to explore whether long-term regional drinking-water hardness is associated with variation in their mineralization profile. Methods: Fifty submandibular sialoliths obtained from 50 patients were analyzed using atomic absorption spectroscopy, optical emission spectroscopy, flame-emission analysis, and photocolorimetric methods. Elemental concentrations were reported as oxide-equivalent weight percentages, and the organic fraction was quantified separately. The molar Ca/P ratio was calculated from CaO- and P₂O₅-equivalent concentrations. Regional drinking-water hardness data for 2018–2026 were obtained from official Armenian water-supply and regulatory sources and expressed in mmol/L. Associations with patient age, sex, geographic region, and long-term regional water hardness were evaluated using non-parametric statistical methods, with correction for multiple comparisons. Results: Calcium was the predominant individual inorganic constituent (CaO-equivalent: 31.38 ± 2.35 wt%), accompanied by P₂O₅ (15.83 ± 2.78 wt%) and a substantial organic fraction (32.09 ± 4.26 wt%). The mean molar Ca/P ratio was 2.62 ± 0.71. CaO and P₂O₅ concentrations were not significantly correlated, indicating considerable heterogeneity in calcium–phosphorus stoichiometry among stones. No significant associations were observed between major compositional parameters and patient age or sex. In contrast, CaO-equivalent content differed significantly among geographic regions (Kruskal–Wallis H = 19.88, p = 0.0058; Holm-adjusted p = 0.0409). Long-term drinking-water hardness ranged from approximately 1.04 to 9.52 mmol/L across the eight regions. At the patient-record level, greater regional water hardness was positively associated with CaO content (Spearman ρ = 0.374, p = 0.0075) and the molar Ca/P ratio (ρ = 0.364, p = 0.0093); however, these associations were attenuated after correction for multiple testing and were not statistically significant when the eight regions were analyzed as independent ecological units. Conclusions: Armenian submandibular sialoliths are chemically heterogeneous composite structures characterized by a calcium- and phosphorus-rich inorganic component and a substantial organic fraction. The significant geographic variability in calcium content and the exploratory positive relationship with regional drinking-water hardness suggest that environmental mineral exposure may contribute to variation in the biomineralization phenotype of sialoliths. However, the ecological nature of the exposure assessment and the absence of significant region-level associations preclude causal inference. Larger prospective studies integrating individual water exposure, salivary biochemistry, and phase-sensitive mineralogical analyses are warranted.