Sialolithiasis: mechanism of calculi formation and etiologic factors

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Abstract

Background: Sialolithiasis is a common disease of salivary glands. The etiology of these calculi is little known and their exact mechanism of formation is unknown. Methods: The composition and structure of 21 sialoliths were studied and the composition of the saliva of each corresponding patient was determined (pH, calcium, magnesium, phosphorus, citrate and phytate). Results: Eighteen sialoliths exhibited similar macro and microstructure, being constituted by hydroxyapatite (HAP) and organic matter, normally arranged in a multilayer structure. The three remaining sialoliths were exclusively constituted by organic matter. The salivary Ca of patients with HAP calculi was significantly higher than that found in the saliva of the healthy group. The salivary phytate concentration of patients with HAP calculi was significantly inferior to that found in patients with calculi exclusively formed by organic matter, as well as to that found in saliva of healthy group. Significant differences between the salivary magnesium concentrations of patients with HAP calculi and the control group were also observed. No significant differences between pH and citrate concentrations of the three groups were found. Conclusions: It was concluded that the deficit of crystallization inhibitors such as myo-inositol hexaphosphate (phytate) was also an important etiologic factor implied in the sialolith development.

Introduction

Sialolithiasis is a common disease of salivary glands characterized by the obstruction of the salivary secretion by a calculus. This is associated with pain and inflammation, and in some occasions with an infection of the affected gland. This disease corresponds to 30% of the salivary pathologies and is more frequent in adults (0.1–1.0% of population) than in children [1], [2], [3], [4].

These calculi generally consist of mixtures of different calcium phosphates (mainly hydroxyapatite and carbonate–apatite) together with an organic matrix [2], [5], [6], [7]. When infection is occasionally present, ammonium and magnesium can be also found.

The etiology of these calculi is little known and their exact mechanism of formation is unknown [3]. The aim of this paper is to study some of the etiologic factors involved with their development, with particular emphasis on those related with saliva composition. Thus, apart from pH and other well-known saliva components (calcium, magnesium, phosphorous, citrate), the presence of myo-inositol hexaphosphate (phytate), a potent crystallization inhibitor of calcium salts [8], [9] was investigated. Phytate is an abundant component of plant seeds and the levels found in blood, urine and mammalian tissues clearly depend on its dietary intake [10], [11].

Section snippets

Materials and methods

Composition and structure of 21 submaxillar sialoliths belonging to 21 different patients were studied following the methodology indicated below.

The saliva of each patient and controls were obtained in the same standard conditions, early in the morning and without eating, smoking, drinking or washing the mouth for at least 2 h before the sample collection. The saliva sample was obtained without stimulation, during a period of 5 min through spitting. All subjects were on free diet at the time of

Results

From the 21 studied submaxillar sialoliths, 18 exhibited similar macro and microstructures, being constituted by hydroxyapatite and organic matter, normally arranged in a multilayer structure (Fig. 1). As can be seen, hydroxyapatite was found as typical spherulites as well as the aspidinic structure. In one of the salivary calculi, next to hydroxyapatite, a little amount of brushite was detected (Fig. 2). The three remaining sialoliths were exclusively constituted by organic matter, exhibiting

Discussion

The macro and microstructure of the hydroxyapatite salivary calculi described in Results is practically identical to those found in the hydroxyapatite renal calculi (non-infective phosphate renal calculi) [14]. Thus, the inner fine structure of both types of hydroxyapatite calculi (salivary and renal) are characterized by an ample occurrence of layers of amorphous material, called “aspidinic” hydroxyapatite layers. Aspidinic layers are unstructured from a macroscopic viewpoint (Fig. 1), but

Acknowledgments

We gratefully acknowledge financial support of Conselleria de Innovacio i Energia of Govern Balear.

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