On the Structural Diversity of Sialoliths António P. Alves de Matos, 1,2, * Patrícia A. Carvalho, 3 Arlindo Almeida, 1 Luís Duarte, 4 Rui Vilar, 3 and Jorge Leitão 1 1 Department of Biomaterials/ITB, Dental Medical School, University of Lisbon, 1649-003 Lisbon, Portugal 2 Anatomic Pathology Department, Curry Cabral Hospital, R. da Beneficência 8, 1069-166 Lisbon, Portugal 3 Department of Materials Engineering, Technical University of Lisbon, 1049-001 Lisbon, Portugal 4 Maxilo-Facial Cirurgy Service, S. José Hospital, 1150-199 Lisbon, Portugal Abstract: Sialoliths from parotid and submaxillar glands have been characterized. Fractured and polished surfaces revealed an intrinsic structural diversity across the calculi sections. In general, the calculi presented highly mineralized amorphous-looking cores surrounded by concentric alternating mineralized and organic layers. The thickness of these layers decreased from the outer regions toward the center of the sialolith, illustrating a sequence of growth stages. Nevertheless, a significant variability could be detected among the specimens. In some cases, the calculi displayed multiple cores and lacked concentric laminated structures. In other instances, the specimens exhibited extensive regions of globular structures. In these cases, the globule diameter decreased across the radius toward the center of the sialoliths, and the globular structures tended to reorganize, forming bright and dark laminated layers surrounding the core. The participation of globular structures in the layer formation process points to morphogenetic mechanisms not previously described. Key words: salivary calculi, sialoliths, conchoidal fracture, laminated structures, sulfur, globular structures I NTRODUCTION Sialolithiasis is a common disease of the salivary glands caused by formation of calculi in the intra- or extraglandu- lar duct system ~Lustmann et al., 1990!, which frequently results in inflammation and infection with accompanying pain. Sialoliths exhibit some structural diversity but usually consist of one or more highly mineralized cores surrounded by approximately concentric laminated structures with alter- nating layers of inorganic and organic substances of vari- able thickness and texture ~Faure et al., 1986!. Chemically, sialoliths are condensations of calcium salts—essentially calcium phosphate and calcium carbonate displaying the hydroxyapatite crystallographic structure— with small amounts of other inorganic and organic compo- nents ~Anneroth et al., 1975!. The main constituent of the calcified regions is hydroxyapatite in the form of crystals with platelike morphologies, which are deposited with vari- able density in a reticular organic matrix ~Tandler, 1965; Tohda et al., 1995!. Other crystallographic forms of calcium phosphate may also be present ~Teymoortash et al., 2003!. The reported structural diversity of sialoliths is a reflec- tion of variations in the nucleation and growth processes. However, the fact that laminated layers are usually described suggests a common underlying growth mechanism ~Anne- roth et al., 1978, Lustmann & Shteyer, 1981; Isacsson & Friskopp, 1984; Grases et al., 2003; Kasaboglu et al., 2004!. In spite of the extensive research carried out on salivary calculi, the essential aspects behind the complex multifacto- rial formation of sialoliths remain obscure and demand fur- ther investigation ~Anneroth et al., 1978; Riesco et al., 1999!. The present work evaluates the structural diversity of sialoliths by ultrastructural characterization and microanalysis. MATERIALS AND METHODS Scanning electron microscopy ~SEM! and energy dispersive spectroscopy ~EDS! have been used to characterize nine sialoliths from parotid and submaxillar glands. The sialoliths, stored in air before processing, were fractured through approximate planes of symmetry, mounted on carbon sup- ports, and coated with carbon in a rotary vacuum evapora- tor. Selected samples were embedded in an epoxy resin, ground with SiC paper, and polished using alumina sus- pensions. Special care was used to minimize mechanical damage during the grinding and polishing steps. SEM ob- servations under secondary electron ~SE! and backscattered electron ~BSE! modes as well as EDS microanalyses were carried out with a Hitachi S2400 instrument operated at 25 kV and equipped with a standard Rontec Si ~Li! detector. Received November 28, 2005; accepted May 1, 2007. *Corresponding author. E-mail: apamatos@kanguru.pt Microsc. Microanal. 13, 390–396, 2007 DOI: 10.1017/S1431927607070754 Microscopy AND Microanalysis © MICROSCOPY SOCIETY OF AMERICA 2007