STEM and HRTEM studies of accumulated deposits on human tooth surface.

The aim of this study was to clarify the fine structure of accumulated deposits on the surface of teeth that are considered to affect the gloss of teeth. The study was carried out using, as specimens, human incisor teeth having gloss, which were extracted from teenage donors and those incapable of showing gloss even by brushing which were extracted from donors in their 50s. Thin longitudinal sections of tooth enamel with accumulated deposits on the surface were prepared by focused ion beam (FIB) milling, and the fine structure was analyzed using a scanning transmission electron microscope (STEM) and a high resolution transmission electron microscope (HRTEM). By FIB, thin longitudinal sections could be prepared from tooth enamel together with organic and inorganic substances accumulated on the surface without artifacts. The accumulated deposits on the surface of teeth having gloss were composed of organic substances. However, it was first revealed by STEM observation that the accumulated solid deposits on the surface of teeth having no gloss had a complicated structure wherein inorganic and organic substances coexisted. It is suggested that the organic substances contain proteins derived from saliva. The inorganic substances were spherical and needle-like hydroxyapatites (HAs). It is considered that amino acids constituting the proteins affected the nucleus formation and the crystal formation of HA. It is considered that the unevenness of the accumulated deposits existing on the surface of tooth enamel having no gloss causes the decrease in gloss of teeth due to diffuse reflection of light.

Fine structure of tooth enamel in the yellowing human teeth: SEM and HRTEM studies.

OBJECTIVE: The aim of this study was to clarify an influence of the fine structure of human tooth enamel to the yellowing teeth. MATERIALS AND METHODS: Sound maxillary first premolars of 15-50-year-old females that were extracted for the orthodontic treatment were used as the test samples. The tooth enamel sections of these teeth that prepared by ion polishing were observed by scanning electron microscopy (SEM). Furthermore, the fine structure of substance filling the inter-rod spaces was analyzed by high resolution transmission electron microscopy (HRTEM). RESULTS: In white tooth, the inter-rod spaces were observed at the width of about 0.1 µm, while in yellow tooth, the inter-rod spaces were not clearly observed by SEM. HRTEM observations revealed for the first time that the inter-rod spaces were filled with fine particles of poorly crystallized hydroxyapatite in the yellow tooth. In yellow tooth, it was considered that the color of the inner dentin was recognized due to the decrease of light scattering by filling the tooth enamel inter-rod spaces. The generation of particles in the tooth enamel inter-rod spaces was considered to be caused by the long-time progression of calcification. CONCLUSIONS: These results suggested that the change in fine structure, filling in inter-rod spaces of tooth enamel, was related to progression of calcification in the inter-rod spaces with advancing age and one of the factors of yellowness of human tooth.

A novel method for visualizing hair lipids at the cell membrane complex: argon sputter etching/scanning electron microscopy.

Hair lipids localized at the cell membrane complex (CMC) play a part in chemical diffusion, cell cohesion, and mechanical strength. There is no method currently available to visualize hair lipids at the CMC. We found that scanning electron microscopy (SEM) of a transversely polished hair plane followed by argon sputter etching (ASE) provides a specific characteristic image consisting of circular patterns (CP) and stitch patterns (SP) at the cortex. Both the CP and the SP are formed as convex structures and are associated with melanin granules and the CMC, respectively. While the convex formation of the CP is not affected by any treatments tested, that of the SP disappeared following treatment of hair fibers with organic solvents and reappeared following incubation of the solvent-treated hair fibers with melting lipids, which suggests that the hair lipids are responsible for the convex SP. Other treatments, such as chemical fixation, thin sectioning, and pre-/post-incubation of the hair plane, reduce or abolish the convex formation of the SP. These findings suggest that the following pathway leads to the convex formation of SP during ASE: (a) joule heat is generated on the surface by violent collisions of argon ions, (b) melting CMC lipids ooze out from the inside to the surface, and (c) CMC lipids that have oozed out are chemically changed, leading to the final convex formation of the SP. With ASE-SEM, visualization of hair lipids as convex structures of SP should enable us to characterize the fine structure and localization of hair lipids and to clarify the roles and functions of the CMC of human hair.