P. Nolasco

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.

On oral calcifications: sialoliths, dental calculi and tonsilloliths

A.J. Anjos*, P. Nolasco**, J.M. Aquino Marques*, F. Cabrita***, M.F.C. Pereira****, A.P. Alves de Matos***** and P.A. Carvalho** *Faculdade de Medicina Dentaria, Universidade de Lisboa, Cidade Universitaria, 1649-003 Lisboa, Portugal **ICEMS, Instituto Superior Tecnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, Portugal ***Servico de Cirurgia Maxilo-Facial, Centro Hospitalar de Lisboa Central, R. Jose Antonio Serrano 1150-199 Lisboa, Portugal ****CEGPIST, Departamento de Engenharia Civil, Arquitectura e Georrecursos, Instituto Superior Tecnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, Portugal *****Anatomia Patologica, Centro Hospitalar de Lisboa Central - HCC, Rua da Beneficencia 8, 1069-166 Lisboa; Centro de Estudos do Ambiente e do Mar (CESAM/FCUL) - Faculdade de Ciencias da Universidade de Lisboa and Centro de Investigacao Interdisciplinar Egas Moniz (CiiEM), Quinta da Granja , Monte de Caparica, 2829-511 Caparica, Portugal The oral cavity is susceptible to several calcifications such as salivary calculi (sialoliths), dental calculus (tartar) and tonsillar concretions (tonsilloliths). Although several individual studies had been already carried out, a comprehensive morphological and elemental comparison between them is still missing. Sialoliths are most commonly found in the submandibular glands [1] and are composed of regions rich in Ca and P minerals, namely hydroxyapatite, whitlockite and brushite [1], and regions consisting of organic matter with high-sulphur content [1]. These regions are organized in alternating concentric layers [1]. Several bacterial species have also been identified in sialoliths microstructure showing that infection occurs recurrently throughout the stone formation [2]. Generally, tartar presents an inorganic structure rich in Ca and P minerals, such as brushite, octacalcium phosphate, hydroxyapatite and whitlockite, and an organic matrix, mainly constituted by aerobic bacteria and yeast or just anaerobic bacteria [3]. Tonsilloliths occur most commonly on the crypts of the palatal tonsils and are composed of a mixture of organic matter, namely bacterial cells and epithelial debris, as well as inorganic material rich in Ca and P minerals such as hydroxyapatite. Volatile sulphur compounds produced by anaerobic bacteria are usually associated to these, in general, innocuous structures [4]. The current study involved the ultrastructure and chemical characterization of the calcified structures by scanning electron microscopy (SEM) combined with energy dispersive spectroscopy carried out with a JEOL JSM 7001F instrument with an INCA pentaFetx3 Oxford spectrometer operated at 15 kV. Higher resolution characterization has been performed by transmission electron microscopy (TEM) using a H8100 Hitachi instrument operated at 200 kV. SEM samples were prepared following metallographic procedures [1], whereas TEM samples were obtained following standard biological sample preparation procedures [5]. The results show that sialoliths present the most complex structure, with a central core surrounded by concentric layers, while tartar and tonsilloliths do not have a distinctive architecture (Figures 1 (a), 2 (a) and 3 (a). At higher magnifications, layered structures, as well as crystals could be found in sialoliths and tartar (Figures 1 (b) and 2 (b). Bacteria were common in all the calcified structures, although in tonsilloliths their abundance is higher (Figure 3 (b)). All calcifications have similar elemental constitution, with Ca and P, indicating the presence of calcium phosphates (Figures 1 (c), 2 (c) and 3 (c). Sulphur was also found associated with the organic matter in sialoliths and tonsilloliths, though the amounts found in the latter were much smaller than initially expected. Based on the similarities found, new correlations between these calcification will be available. For instance, the mineralization process described in tartar can help understand the similar processes occurring in sialoliths and tonsilloliths, while the association between bacteria and sulphur in tonsilloliths can be a clue for their presence in

Structural characterization of salivary calculi

The microstructure, local chemistry, crystallography and mechanical properties of submandibular sialoliths have been characterized by powder X-ray diffraction, electron microscopy combined with X-ray spectroscopy and ultramicro-indentation assays. The sialoliths presented highly mineralized, lamellar and globular regions. The fairly homogeneous mineralized regions are constituted by hydroxyapatite, whitlockite and brushite. Lamellar regions consisted of alternating layers of mineralized material and organic matter, with a concentric morphology pointing to a chronologic cyclic formation. Globular regions are composed of organic matter globules presenting high sulphur content. The Young modulus and hardness increased with the mineralization degree of the sialoliths. Nevertheless the relatively high amounts of compliant and soft organic matter present in the sialoliths may play a major role in the relatively low success of shock wave therapeutics for sialolith fragmentation.

Structural typologies of salivary calculi

P. Nolasco*, A.J. Anjos**, J.M. Aquino Marques**, F. Cabrita***, M.F.C. Pereira****, A.P. Alves de Matos***** and P.A. Carvalho* *ICEMS, Instituto Superior Tecnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, Portugal **Faculdade de Medicina Dentaria, Universidade de Lisboa, Cidade Universitaria, 1649-003 Lisboa, Portugal ***Servico de Cirurgia Maxilo-Facial, Centro Hospitalar de Lisboa Central, R. Jose Antonio Serrano 1150-199 Lisboa, Portugal ****CEGPIST, Departamento de Engenharia Civil, Arquitectura e Georrecursos, Instituto Superior Tecnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, Portugal *****Anatomia Patologica, Centro Hospitalar de Lisboa Central - HCC, Rua da Beneficencia 8, 1069-166 Lisboa; Centro de Estudos do Ambiente e do Mar (CESAM/FCUL) - Faculdade de Ciencias da Universidade de Lisboa and Centro de Investigacao Interdisciplinar Egas Moniz (CiiEM), Quinta da Granja , Monte de Caparica, 2829-511 Caparica, Portugal Several theories have been put forward regarding the aetiology and pathogenesis of salivary calculi, although a comprehensive understanding of the nucleation and growth mechanisms involved in the formation of these structures is still lacking. In general, sialoliths present one core partially or highly mineralized surrounded by concentric layers of organic and mineralized matter that alternate in succession following a chronologic sequence [1]. The layers consist of fine mineralized strata intercalated with fine organic ones and threaded globular structures with variable degrees of mineralization [1]. The exact mechanism involved in the genesis of sialoliths remains largely unknown, theories defending an initial organic nidus or an initial precipitation of minerals, with subsequent deposition of organic and inorganic layers, can be found in the literature [2-4]. Nevertheless, it remains object of discussion the etiologic factors responsible for the formation of the first nidus or the initial precipitation, since infection, inflammation of the gland, viscous nature of the mucous secretions or naturally existing sialomicroliths have all have been implicated [4-6]. Aiming at an exhaustive systematization of salivary calculi morphogenesis, their morphology has been studied by micro-computed tomography (μCT) and scanning electron microscopy (SEM). μCT studies were done on as-extracted dried samples using μCT SkyScan 1172 instrument with a 1.3 Megapixel camera, operated at the maximum available power of the source (10W). Radiographs acquisition was performed with a rotational step in the 0.70-1