On the structural diversity of sialoliths

Histopathology and ultrastructural findings of pediatric sialolithiasis: a brief communication

Sialolithiasis is a condition in which the salivary gland excretory duct is obstructed due to the formation of calcareous deposits and is uncommon in children compared to adults. The treatment modalities range from a conservative approach involving hydration to a surgical approach. Though several studies have analyzed the sialolith micromorphology structures, studies on pediatric sialoliths remain scarce. This brief communication aims to describe the sialolith micromorphology to understand the mechanism of mineralization and growth of pediatric sialoliths. A 6-year-old Korean female presented with swelling under her tongue. The intraoral examination revealed a painless yellowish hard mass beneath the tongue near the Wharton’s duct which was suspected as a sialolith. After receiving the informed consent, the sialolithotomy was performed under local anesthesia. The obtained stone was analyzed through histopathology and transmission electron microscope examinations to understand the mechanism of mineralization and growth of pediatric sialolith. The micromorphology and growth processes of pediatric sialolith remain undescribed. More comprehensive microscopic studies are needed regarding their distinctive characteristics. By expanding knowledge about sialoliths micromorphology, development of new preventive, diagnostic and patient-tailored treatment methods of pediatric sialolithiasis will be enhanced.

Mineralization of Sialoliths Investigated by Ex Vivo and In Vivo X-ray Computed Tomography

The fraction of organic matter present affects the fragmentation behavior of sialoliths; thus, pretherapeutic information on the degree of mineralization is relevant for a correct selection of lithotripsy procedures. This work proposes a methodology for in vivo characterization of salivary calculi in the pretherapeutic context. Sialoliths were characterized in detail by X-ray computed microtomography (μCT) in combination with atomic emission spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Correlative analysis of the same specimens was performed by in vivo and ex vivo helical computed tomography (HCT) and ex vivo μCT. The mineral matter in the sialoliths consisted essentially of apatite (89 vol%) and whitlockite (11 vol%) with average density of 1.8 g/cm3. In hydrated conditions, the mineral mass prevailed with 53 ± 13 wt%, whereas the organic matter, with a density of 1.2 g/cm3, occupied 65 ± 10% of the sialoliths' volume. A quantitative relation between sialoliths mineral density and X-ray attenuation is proposed for both HCT and μCT.

Local Response of Sialoliths to Lithotripsy: Cues on Fragmentation Outcome

Lithotripsy methods show relatively low efficiency in the fragmentation of sialoliths compared with the success rates achieved in the destruction of renal calculi. However, the information available on the mechanical behavior of sialoliths is limited and their apparently tougher response is not fully understood. This work evaluates the hardness and Young's modulus of sialoliths at different scales and analyzes specific damage patterns induced in these calcified structures by ultrasonic vibrations, pneumoballistic impacts, shock waves, and laser ablation. A clear correlation between local mechanical properties and ultrastructure/chemistry has been established: sialoliths are composite materials consisting of hard and soft components of mineralized and organic nature, respectively. Ultrasonic and pneumoballistic reverberations damage preferentially highly mineralized regions, leaving relatively unaffected the surrounding organic matter. In contrast, shock waves leach the organic component and lead to erosion of the overall structure. Laser ablation destroys homogeneously the irradiated zones regardless of the mineralized/organic nature of the underlying ultrastructure; however, damage is less extensive than with mechanical methods. Overall, the present results show that composition and internal structure are key features behind sialoliths' comminution behavior and that the organic matter contributes to reduce the therapeutic efficiency of lithotripsy methods.

Characterization of a submandibular gland sialolith: micromorphology, crystalline structure, and chemical compositions

OBJECTIVE

The aim of this study was to understand the mechanism of mineralization and growth of a sialolith by analyzing its micromorphology, crystalline structure, and chemical compositions.

STUDY DESIGN

A sialolith was removed along with submandibular salivary gland from a patient. After cross-cutting and polishing the sialolith, its morphology, chemical compositions, crystalline structure, and chemical states were analyzed by using optical camera, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffractometer, Fourier transform infrared spectrophotometer, and transmittance electron microscopy.

RESULTS

The sialolith had a core composed of organic material, such as lipid compounds, and the surrounding mineralized shell structure mostly consisted of hydroxyapatite. In the transition zone between the organic core and mineralized shell layers, inorganic layers were arranged alternately with organic layers. Congregated globular structures were calcified with hydroxyapatite and whitlockite crystallites. Analysis of crystalline structures and chemical compositions suggested that calcium phosphate minerals containing magnesium, such as whitlockite, were developed in the initial stage and gradually transformed into crystallites composed of hydroxyapatite during the growth of crystallites.

CONCLUSIONS

Sialolith with an organic core grew as inorganic materials were deposited and calcified in alternate layers. The mineralization process might include the initial whitlockite development and successive transformation into more stable hydroxyapatite.

Structure and growth of sialoliths: computed microtomography and electron microscopy investigation of 30 specimens

Theories have been put forward on the etiology of sialoliths; however, a comprehensive understanding of their growth mechanisms is lacking. In an attempt to fill this gap, the current study has evaluated the internal architecture and growth patterns of a set of 30 independent specimens of sialoliths characterized at different scales by computed microtomography and electron microscopy. Tomography reconstructions showed cores in most of the sialoliths. The cores were surrounded by concentric or irregular patterns with variable degrees of mineralization. Regardless of the patterns, at finer scales the sialoliths consisted of banded and globular structures. The distribution of precipitates in the banded structures is compatible with a Liesegang-Ostwald phenomenon. On the other hand, the globular structures appear to arise from surface tension effects and to develop self-similar features as a result of a viscous fingering process. Electron diffraction patterns demonstrated that Ca- and P-based electrolytes crystallize in a structure close to that of hydroxyapatite. The organic matter contained sulfur with apparent origin from sulfated components of secretory material. These results cast new light on the mechanisms involved in the formation of sialoliths.