Evolutionary conformation model of salivary gland lithiasis
Authors: Barrueco Álvaro Sánchez , López-Acevedo María Victoria , Sanzen-Baker William Aragonés , López-Andrés Sol , Tapia Gonzalo Díaz , Rueda Ignacio Alcalá , Coello Jessica Mireya Santillán , Español Carlos Cenjor , Aubá José Miguel Villacampa 
Published: October 2024

Introduction
Salivary stones, or sialoliths, are calcified concretions that form in the salivary glands and their ducts. The formation of sialoliths follows a two-stage process: an initial stage that creates a central core through the precipitation of inorganic material mediated by organic substances, and a second stage involving the accumulation of layers of organic and inorganic material. Sialoliths can form on different types of substrates, including agglomerates of mucoid material, organic vesicles, or foreign bodies, and may be associated with bacterial infections. A detailed analysis of the structure of salivary origin lithiasis can provide information to develop specific therapies to prevent their genesis and/or subsequent growth.
Materials and Methods
This study is based on 137 sialoliths obtained from 102 patients treated at three university hospitals. The stones were obtained through sialendoscopy, direct extraction, or spontaneous extrusion. Morphological and compositional studies were performed using scanning electron microscopy (SEM-EDX) and X-ray diffraction (XRD).
Results
Most sialoliths were extracted from the submaxillary gland (82%), with the remainder from the parotid gland (18%). They exhibited varied shapes, with irregular morphologies predominating in the parotid stones and ellipsoidal forms in the submaxillary stones. The sialoliths were oolitic aggregates with a well-defined central core surrounded by concentric layers, associated with the presence of bacteria. The mineral composition included octacalcium phosphate, hydroxyapatite, and whitlockite. A direct relationship was observed between the size of the sialolith and the higher proportion of hydroxyapatite (which presents a greater degree of crystallinity than OCP).
Discussion
Sialoliths exhibit common morphological and compositional characteristics despite their varied origins. Their formation begins with the heterogeneous nucleation of calcium phosphates on organic spherules, probably induced by bacterial biofilms. These spherules aggregate to form a central core upon which layers of organic and inorganic material are added. Over time, the sialolith grows, increasing in size and the crystallinity of the involved mineral phase. The presence of amorphous phases and the heterogeneity of the layers contribute to the variability observed in sialoliths. Morphological and compositional analysis using SEM-EDX has enabled the development of a conformational model applicable to all sialoliths, regardless of their origin, location, and associated demographics.
Conclusions
Sialoliths are oolitic crystalline aggregates with a central core surrounded by concentric layers of organic and inorganic material. Their formation begins with heterogeneous nucleation around organic spherules, facilitated by the presence of bacterial biofilms. As the sialoliths grow, their complexity and crystallinity increase. The conformational model proposed by our research group highlights the interaction between organic matter, inorganic matter, bacterial germs, and time as key factors in the formation of sialoliths. This novel model is applicable to all sialoliths regardless of interpersonal differences and their origin.