Title: Classification of submandibular salivary stones based on ultrastructural studies. A running title: Submandibular gland sialoliths

Introduction: Sialolithiasis remains a clinical problem with unclear etiopathogenesis, lack of prevention methods and only surgical treatment. Materials and Methods: An ultrastructure examination of submandibular sialoliths obtained from patients with chronic sialolithiasis was conducted using a scanning electron microscope and Xray photoelectron spectroscopy. Results: Based on the results, we divided sialoliths into three types: calcified (CAL), organic/lipid (LIP) and mixed (MIX). The core structure of the CAL and MIX is very similar. The core of the LIP has a prevalence of organic components. The intermediate layers’ structure of the CAL is different from LIP and MIX. In LIP and MIX, the organic component begins to increase in intermediate layers rapidly. The structure of the superficial layers for all types of sialoliths is similar. Conclusions: We introduced a new classification of the submandibular salivary gland stones. Based on the results, it can be said that sialoliths type CAL and LIP have their separate path of origin and development, while MIX is formed as CAL stone, and the further pathway of their growth passes as LIP stones. Organic components was much more than inorganic in all layers of salivary gland stones, which highly prevents their dissolution in the patient’s salivary gland duct.