BackgroundProviding comprehensive knowledge of the anatomy of human teeth is one of the basic functions of dental education, because a thorough understanding of their internal structure is one of the prerequisites for any successful clinical intervention. Several techniques have traditionally been employed to study and visualize the complex internal organization of human teeth. In contrast to these invasive techniques, modern imaging systems permit non-invasive analyses of the three-dimensional structure of human teeth. Owing to the relative ease of acquisition, handling, and distribution of the respective data, digital imaging techniques will also significantly influence dental education. HighlightIn this article, a broad overview of traditional and modern techniques for the visualization of internal tooth structures is provided. Emphasis is placed on micro-computed tomography systems and their application in endodontics. In addition, 3 the results derived from a comparison of histology and micro-computed tomography are presented. Apart from its utility in basic research, digital data can also be employed to create interactive three-dimensional models that are particularly suitable for teaching purposes. ConclusionNon-invasive, three-dimensional imaging techniques, in particular the various modalities of computed tomography, have ushered in a new era of endodontic studies.Owing to their digital nature, the results derived from these techniques can not only be easily analyzed and distributed but also be rapidly integrated into the teaching materials. Recent studies as well as the data shown in the present contribution suggest that digital educational materials lead to an improved understanding of the complex anatomy of human teeth.

Water-clear cells and transitional forms between the chief cells and water-clear cells were observed in the parathyroid gland of the golden hamster. Their ultrastructure is described, and the origin of the water-clear cell is discussed.

The ultrastructure of the parathyroid glands of golden hamsters subjected to 5-gravity environment after administration of epinephrine was studied. In the epinephrine-treated animals exposed to a hypergravity environment, the Golgi complexes associated with numerous prosecretory granules were significantly increased compared with those of the control centrifuged and epinephrine-treated animals as well as the cisternae of the granular endoplasmic reticulum compared with those of the control and centrifuged animals. In addition, many secretory granules were situated close to the the plasma membrane of the chief cells in the epinephrine-treated animals exposed to a hypergravity environment. Those observations suggest that the secretory activity of the parathyroid gland may be markedly stimulated in the epinephrine-treated animals exposed to a hypergravity environment.

Endogenous peroxidase activity in the submandibular gland of the house musk shrew, Suncus murinus was cytochemically investigated by light and electron microscopy using 3,3'-diaminobenzidine-tetrahydrochloride salt (DAB). The submandibular glands of male Suncus murinus at 8-month-olds were excised and diced into small pieces. In general, salivary glands are structurally divided into a terminal portion comprising a secretory portion and duct system. The submandibular gland of the Suncus murinus, the terminal portions consisted of proximal and distal acinar cells. On the other hand, a granular duct cell of the duct system contained a number of characteristic myelin-like bodies. In the present study, the peroxidase reaction products were localized in the secretory granules of the proximal acinar cells and in the endoplasmic reticulum, Golgi apparatus and myelin-like bodies of the granular duct cells. These reaction products were reduced when 5 mM 3-amino-1,2,4-triazole was added to the reaction medium. Additionally, release of peroxidase into the lumen was observed. In conclusion, the proximal acinar and granular duct cells formed peroxidase and may have performed excretory secretions. Moreover, the peroxidase positive myelin-like body consisted of lamellated membrane and its outer surface membrane continued to the endoplasmic reticulum.

Effects of 5-gravity environment on the ultrastructure of the parathyroid glands of norepinephrine-treated golden hamsters were studied. In the centrifuged animals treated with norepinephrine, the volume density occupied by the Golgi complexes associated with numerous prosecretory granules was significantly increased compared with that of the control, centrifuged and norepinephrine-treated animals, as well as the volume density occupied by the cisternae of the granular endoplasmic reticulum compared with that of the control and centrifuged animals. In addition, in the centrifuged animals treated with norepinephrine, numerous secretory granules were situated close to the plasma membrane. It is suggested that the synthesis and release of secretory granules may be markedly stimulated in the parathyroid glands of the norepinephrine-treated golden hamsters subjected to a hypergravity environment.