Histologic study of biocompatibility of the "Cristaloy 7-N" alloy.

The most commonly used alloy in dentistry practice in metal-ceramic prosthetic constructions is cobalt-chromium-molybdenum alloy. In Bulgaria the company "Sandental" created a nickel-based alloy for metal-ceramic prostheses. The aim of the study was to asses the medicobiological properties of the nickel-chromium-molybdenum alloy "Cristaloy 7-N". The study was performed on eight guinea pigs and four white rats. On both sides of the vertebral column, parallel to it, experimental plates of "Cristaloy 7-N" were implanted on one of the sides and on the contralateral side - golden alloy - .916 gold. After a different period of time - 10, 30, and 90 days, the experimental animals were eutanized and the tissues adjacent to the implanted experimental plates were studied. During the whole period of the study a skin or local or general reaction was not observed. There was no difference in succinate-dehydrogenase activity that is a sign for preserved vital activity. The electron microscopic study of the cells in contact to the implant showed normal ultrastructure of the organelles. The results obtained from the histological, histochemical and electron microscopic study gave evidence for characterizing the alloy "Cristaloy 7-N" as one having high biocompatibility.

Ultrastructure of cultures from embryonic human gonads.

We present the results from experimental studies of the ultrastructural changes taking place in the oogonia and spermatogonia under conditions of in vitro culturing. The investigations were performed on gonads of 8-gestation- week-old human embryos. They were examined in vitro using a Georgiev diffusion chamber. It was established that during explantation the oogonia display a higher level of organisation of their cell structures and develop at the same rate as they do in the body, while the spermatogonia delay their differentiation preserving many of the features of undifferentiated cell types. These changes are specific and can be used as early morphological criteria for distinguishing one cell type from the other.

Ultrastructure of the human APUD cells.

The present article summarises the results of our studies on the ultrastructure of the APUD cells at an early embryonic stage of development. Twenty eight 8-week-old human embryos were selected. The early forms of the APUD cells in the epithelium of certain embryonic organs of endoblast origin, i.e., stomach, small intestine, liver and lung (bronchi), were distinguished and examined by transmission electron microscopy. The ultrastructure of these premature cells was compared with the ultrastructure of mature APUD cells from adult human organisms. Differences regarding number, size and location of the secretory granules were established. The form and ultrastructure of the granules were found to be identical in both cell types studied. The ultrastructural characteristics and identification of the embryonic APUD cells may serve as a reliable criterion in complex morphological explorations of the human prenatal development.

[Lysosomes in embryonic cell differentiation]. / Lizozomite v embrionalnata kletuchna diferentsiatsiia.

Lysosomes as a modeling factor of embryonal morphogenesis occupy an important place in the systemic structural and ultrastructural studies on prenatal development of man. Human embryos at the age of 6 to 10 weeks of embryonal development, obtained after interruption of normal pregnancy by the method vacuum excochleation according to Andreev. Lysosomes were investigated in cells of groups, chosen in advance, from organs with various origin and degree of cellular differentiation: neurones of the spinal cord and spinal ganglia, keratinocytes of the epidermis, epithelium of lentil vesicle, chondrocytes of Merkel's cartilage, epithelium of intestines and bronchi, hepatocytes, myoblasts, corticocytes, of coelomic fetal and definitive cortex of the adrenal, metanephros, coelomic epithelium of gonad, epithelium of Mueller's duct and Wolff's ducts, hemopoietic foci and capillary vasothelium. Lysosomes were divided into three groups: primary lysosomes, secondary autolysosomes and cytosomes. Lysosomes participate in the following processes during the course of embryonal organogenesis: 1. destruction of cells of transient embryonal organs; 2. destruction and demolition of whole cells during the course of normal embryonal development; covering with a membrane and lysis of inferior cellular organelles; 5. lysis with consecutive assimilation of cytoplasmic inclusion; lysis of secretory products.