Biomedical subjects
Publications and source records attributed to G Daculsi.
Ion thinning technique applied to high resolution T.E.M. study of human dental enamel crystallites makes it possible to visualize a great number of dislocations. Dislocations proved not to be due to artifacts induced by the ultramicrotome diamond knife. They are related to the crystal apartite structure.
High resolution electron microscopy now makes it possible to use an original method for measuring biological apatite crystals. The crystals of intertubular sound dentine have an average width of 296 A (standard deviation: 37) and an average thickness of 32 A (standard deviation: 5). During the course of so-called arrested caries, crystals get twice as thick compared to those sound dentine, whereas their width remains unchanged.
TEM, SEM and X-ray diffraction analysis demonstrate the heterogeneity of the dentinal tissue on Anarhichas lupus, a vascular osteodentine. The disordered aspect of collagen fibres, incompletely mineralized (the periodical striation being still visible), explains the scattered distribution of crystallites since they are responsible for their arrangement. The low degree of mineralization revealed by the visible collagen striation is confirmed by X-ray diffraction analysis (the crystallinity of vascular osteodentine being much lower than that of the peripheral dental tissue) as well as by high resolution TEM, since no lattice planes could be observed. Osteodentine, supporting bone and proper bone have in common a mineral phase, more or less organized, different from the apatite system.
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An ultrastructural study of teeth with amelogenesis imperfecta revealed various aspects of microcavities in the enamel surface, which ranged from isolated imprints of ameloblasts corresponding to the mildest lesions at the end of amelogenesis, to pits caused by the death of 20 to 30 ameloblasts at the beginning of amelogenesis. Abnormalities in the shape of the prisms can be observed. Further, crystals are distributed randomly within a prism or at the junction of 2 contiguous prisms while intercrystalline spaces are widened, indicating in various places the lack of a preferred orientation of the crystals. In amelogenesis imperfecta, two different crystalline periods are found: 1 of about 250 A, the other of about 500 A and over. The fact that amorphous areas are found among the crystals of enamel may be related to different stages of crystallization. However, it was not possible to find any lattice defect.
High resolution electron microscope techniques now make it possible to study the mineralization of calcified tissues at the crystal structure level. Dislocations play an important part in the course of crystal maturation and modifications. At least two origins of dislocations are known. The first is due to phenomena related to the incorporation of fluoride ions into the lattice. The second is due to mechanical stresses occurring between crystals during their maturation. Dislocations are the starting-points of acid dissolution which proceeds along dislocation-lines, sometimes inducing a splitting of the crystals. In the present study, dislocations have been visualized, either isolated in the crystal core and perhaps the two-dimensional surface representation of a screw-shaped dislocation, or forming nets of dislocations producing a spiral staircase on the sides faces of the crystals. There is evidence of a maturation cycle of the crystals, which may grow, split, coalesce or dissolve; liberated elements and small crystal fragments may allow development of near-by crystals. This remodelling explains the existence of a standard size as well as the perfect fitting of the crystals. These morphological data involve physico-chemical properties of biological apatites.
80 golden hamsters received Keyes high carbohydrate diet 2 000 and a therapy with the unsaponified fraction of corn germ oil extract (UCOE). 40 hemialveolar molar sockets were preserved and a quantitative study was carried out with the scanning electron microscope and the use of two statistical methods. The effects of UCOED are: a reduction of resorption areas, a decrease in size of resorption lacunae and an increase in the attachment surface of periodontal fibres. These results are connected to the quantity of UCOED ingested. Further, the quantifying of the resorption areas indicates that the periodontal lesions induced by Keyes diet 2 000 are balanced by the ingestion of 20 mg/kg/per day of UCOED, whereas the ingestion of 50 mg/kg/per day induced a larger increase in bone apposition.
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Teeth with amelogenesis imperfecta were obtained from three members of the same family, and studied through convergent technics of investigation: classical histology, scanning electron microscopy, high resolution electron microscopy, and crystallographic analysis. The results were compared with theoretical computer calculations. Enamel abnormalities related to the shape and irregular distribution of the crystals. Some needle-shaped crystals were found together with large ones, roughly rectangular. 42% of the crystals were distorted. Widened interplanar spacings were evidence of an hypomineralization. However, the interplanar spacings observed in high resolution electron microscopy, as well as the crystalline degree of the crystals, studied through classical crystallographic methods, revealed an apparently sound hydroxyapatite
The use of physico-chemical and microscopic technics shows that in carie-free fluorotic enamel well-ordered, closely packed, parallelepiped-like crystals can be found as well as hypomineralized areas in which the crystals are disordered and the interprismatic gaps widened. The observation of 1340 crystals shows an increase in their diameter measurements (600 to 700 A instead of 400 to 500 A) and alterations in their morphology, the faces of the crystals remaining nevertheless welldeveloped, in perfect agreement and their hexagonal symmetry. Together with the increase of the fluorosis index, it must be noted that fluoroapatite is progressively filling the place of hydroxyapatite. The coexistence of two different types of apatites within the crystals might be responsible for lattice dislocations involving a greater fragility of the central part of the crystals. The fact that fluoroapatite is very likely localized in the outer part of the crystals could be the reason why they are better resisting demineralization. The central holes within the crystals are not specific of fluorosis, they might rather by due to a demineralization carious process.
48 male goldern hamsters 5 weeks old were divided in 4 groups. The first group was used as control. The second was submitted to the 2 000 cariogenic Keyes diet inducing severe alveolar bone resorption. The third and fourth group received with the same diet a thyrocalcitonin injection every two days (3rd group) and every day (4th group) during three months. The study of the alveolar plates with the scanning electron microscope in the animal having received thyrocalcitonin showed a reduced number of resorption lacunae, a denser bone surface covered by a homogeneous and dense granular material similar to that observed in the controls. The calcified globules, constituting the bone anchoring of the Sharpey's fibres, were different from those of the second group submitted to Keyes diet and similar to the controls.
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A total of 60 cylindrical 6 x 6 mm samples of a macroporous biphasic calcium phosphate (MBCP) ceramic were implanted into a distal femoral site in 30 rabbits. These samples represented six kinds of implants with two different macropore diameters and three different macroporosity percentages. Analysis of backscattered electron images of implant surfaces analysed by a factorial design method showed that implants with 565 microm pore size provided more abundant newly formed bone both in peripheral and deep pores than those with 300 microm pore size. No significant differences were found between implants with 40 and 50% macroporosity, suggesting that the influence of macropore size on bone ingrowth was greater than that of macroporosity percentage. MBCP implants with 565 microm pore diameter and 40% macroporosity represented the optimal association for homogeneous and abundant bone ingrowth.
PURPOSE: To analyze LGM Vena Tech filter incorporation and the rapidity of the process. MATERIALS AND METHODS: A filter was inserted into the infrarenal inferior vena cava (IVC) of 15 ewes assigned to one of three groups depending on the length of follow-up (2, 4, or 8 weeks). Radiologic data concerning IVC diameter and filter patency, stability, and incorporation were obtained before and after insertion and before euthanasia. Histopathologic analysis concerned wall thickness and smooth muscle cell area (SMCA) at three levels of the filter and at one point outside the filter. RESULTS: All filters remained patent during follow-up. Incorporation of struts was dependent on time (P = .006), level of the filter (P = .0001), and strut surface (P < .0001). Neointimal thickness increased during follow-up (P = .0002), being more marked in the midportion of the filter (P = .0037). Adventitial thinning was observed (P = .0001), corresponding to a significant decrease in SMCA (P < .0001) above the struts as a function of the length of the follow-up period (P = .0021). CONCLUSIONS: The LGM Vena Tech filter was well tolerated and is suitable for incorporation into the IVC wall of normal animals without risk of any deleterious reactions due to biological incompatibility.
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