Evolutionary conformation model of salivary gland lithiasis

Alvaro Sánchez Barrueco^1,2,3*María Victoria López-Acevedo Cornejo⁴William Aragonés Sanzen-Baker^2,3Sol López-Andrés⁴Gonzalo Díaz Tapia^1,2,3Ignacio Alcalá Rueda^2,3Jessica Mireya Santillán Coello^1,2,3Carlos Cenjor Español^1,5Jose Miguel Villacampa^1,5

• ¹University Hospital Fundación Jiménez Díaz, Madrid, Spain
• ²Hospital General de Villalba, Villalba, Madrid, Spain
• ³Alfonso X el Sabio University, Villanueva de la Cañada, Madrid, Spain
• ⁴Department of Mineralogy and Petrology, Faculty of Geological Sciences, Complutense University of Madrid, Madrid, Madrid, Spain
• ⁵Autonomous University of Madrid, Madrid, Madrid, Spain

IntroductionSalivary stones, or sialoliths, are calcified concretions forming within salivary glands and their ducts through a two-stage process: an initial formation of a central core via precipitation of inorganic material mediated by organic substances, followed by layering of additional organic and inorganic material. Substrates for sialolith formation include mucoid agglomerates, organic vesicles, foreign bodies, and bacterial biofilms. Understanding the detailed structure of sialoliths may aid in developing specific preventive or therapeutic strategies.Materials and MethodsThis study analyzed 137 sialoliths from 102 patients treated across three university hospitals. Stones were extracted via sialendoscopy, direct extraction, or spontaneous extrusion. Structural and compositional analyses were conducted using scanning electron microscopy (SEM-EDX) and X-ray diffraction (XRD).ResultsMost sialoliths were from the submandibular gland (82%), with the remainder from the parotid gland (18%). Parotid stones predominantly exhibited irregular shapes, while submandibular stones were generally ellipsoidal. All stones demonstrated an oolitic structure characterized by a central core surrounded by concentric layers and frequently associated with bacteria. Mineral composition predominantly included octacalcium phosphate (OCP), hydroxyapatite, and whitlockite. Larger sialoliths exhibited a higher proportion of hydroxyapatite, indicating increased crystallinity compared to OCP.DiscussionDespite diverse origins and locations, sialoliths share common morphological and compositional traits. Their formation begins with heterogeneous nucleation of calcium phosphates around organic spherules, likely induced by bacterial biofilms. These initial nuclei aggregate into a central core upon which additional layers of organic and inorganic materials deposit progressively. This layering increases the size and crystallinity of the sialoliths over time. The coexistence of amorphous phases and structural heterogeneity within layers explains the variability among stones. Detailed SEM-EDX analysis supports a unified conformational model for sialoliths that integrates the interplay of organic substrates, inorganic minerals, bacterial biofilms, and temporal factors.ConclusionsSialoliths are oolitic aggregates featuring a central core surrounded by concentric layers composed of organic and inorganic materials. Their formation process involves initial heterogeneous nucleation, bacterial influence, and progressive crystallization. This universal conformational model effectively describes sialolith formation irrespective of patient-specific or anatomical variations.