Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0432222 (SEM)
 47,337 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effect of time at 600 degrees C and of small additions of Al2O3 and B2O3 on the sintering of two composite materials of (1) hydroxylapatite (Ca10(PO4)6(OH)2) and bioactive glass (SiO2-CaO-P2O5-Na2O) or (2) rhenanite (CaNaPO4) and bioactive glass were studied. Scanning microscopy, quantitative EDX, x-ray diffraction, helium gas density measurements, and diametral measurements were performed on the resulting composites. No reactions were observed with the SEM or XRD between the hydroxylapatite particles and the glass matrix within sufficient sintering times to achieve maximum density. The rheunanite-containing composites were observed to form Na2O2CaO3SiO2 crystals by x-ray diffraction, probably as a result of dissolution of the rhenanite particle surfaces into the glass phase, the crystals formed in the glass or at the interface of the glass, and the ceramic particles. However, within the short sintering times needed to achieve maximum density the rhenanite particles remained mostly intact. The rhenanite-containing materials gave better results than the hydroxylapatite-containing materials. The glass composition had a great effect on the densification process.
 ...
PMID:Preparation of dense hydroxylapatite or rhenanite containing bioactive glass composites. 132 42

Glass-ceramics containing crystalline oxy-fluoroapatite (Ca10(PO4)6(O,F2)) and wollastonite (CaSiO3) (designated AWGC) are reported to have a fairly high mechanical strength as well as the capability of forming a chemical bond with bone tissue. The chemical composition is MgO 4.6, CaO 44.9, SiO2 34.2, P2O5 16.3, and CaF2 0.5 in weight ratio. In this study the influence of substituting B2O3 for CaF2 on the bonding behaviour of glass-ceramics containing apatite and wollastonite to bone tissue was investigated. Two kinds of glass-ceramics containing apatite and wollastonite were prepared. CaF2 0.5 was replaced with B2O3 at 0.5 and 2.0 in weight ratio (designated AWGC-0.5B and AWGC-2.0B). Rectangular ceramic plates (15 x 10 x 2 mm, abraded with No. 2000 alumina powder) were implanted into a rabbit tibia. The failure load, when an implant detached from the bone, or the bone itself broke, was measured. The failure load of AWGC-0.5B was 8.00 +/- 1.82 kg at 10 weeks after implantation and 8.16 +/- 1.36 kg at 25 weeks after implantation. The failure load of AWGC-2B was 8.08 +/- 1.70 kg at 10 weeks after implantation and 9.92 +/- 2.46 kg at 25 weeks after implantation. None of the loads for the two kinds of glass-ceramics decreased as time passed. Giemsa surface staining and contact microradiography revealed direct bonding between glass-ceramics and bone. SEM-EPMA showed a calcium-phosphorus rich layer (reaction zone) at the interface of ceramics and bone tissue. The thickness of the reaction zone was 10 to -15 microns and did not increase as time passed.(ABSTRACT TRUNCATED AT 250 WORDS)
 ...
PMID:Influence of substituting B2O3 for CaF2 on the bonding behaviour to bone of glass-ceramics containing apatite and wollastonite. 161 Sep 64

This paper introduces the composition of Castabe Glass-Ceramic (CGC), synthetic technique and physical and chemical properties. By means of TEM, SEM, XRD and EPMA techniques, the structure of CGC on K2O-MgO-Al2O-SiO2-F glass, type and size of crystallization are investigated. The results are as follows: the main crystal phase is tetrasilicic flourmica (K2Mg2.5Si4-O10F2), refractive index = 1.53, transparency = 48%, Density = 2.7 g/cm3, elastic modulus = 68.22 GPa, breaking strength = 141.1 MPa, breaking durability = 1.83 and V. H. = 505 kg/mm2. Base the above properties described, the function of CGC is similar to the Dicor (Dentsply. Int. U. S. A.) which is one of the well known material in western countries in now days.
 ...
PMID:[Castable glass-ceramic-synthesizing and testing]. 181 64

An apatite- and wollastonite-containing glass-ceramic (A.W-GC) has been reported to form a tight bond with living bone through an apatite layer formed on its surface. This layer is considered to be formed by dissolution of Ca2+ and HSiO3- ions from the glass-ceramic into the surrounding body fluids. In order to confirm this proposed mechanism for the surface reaction of A.W-GC, three kinds of glass in the systems CaO-SiO2, CaO-SiO2-CaF2, and CaO-SiO2-P2O5 were implanted into the tibiae of rabbits for 3 or 8 weeks. Contact microradiography and SEM-EPMA showed that all three kinds of glass formed a Ca,P-rich layer in combination with a Si-rich layer on their surfaces within 3 weeks and formed a direct bond with bone via these layers. The detaching test, performed 8 weeks after implantation, showed that the loads required to detach the implants from the bone were almost equal for the phosphorus-free and the phosphorus-containing glasses. It was concluded that even P2O5-free CaO.SiO2 glass formed a Ca,P-rich layer on its surface and bonded tightly with living bone. If glasses and glass-ceramics release at least Ca2+ and HSiO3- ions, this would be sufficient for them to form the Ca,P-rich layer on their surfaces in vivo, enabling them to bond directly with bone.
 ...
PMID:Bone-bonding ability of P2O5-free CaO.SiO2 glasses. 202 40

The purpose of this study is to examine the formation of hydroxyapatite on the surface of glass-ceramics (chemical composition: SiO2, 34.2; P2O5, 16.3; CaO, 44.9; MgO, 4.6; CaF2, 0.5 in weight ratio). Two experiments were performed. In the first experiment, plates (2 x 25 x 25 mm) of glass-ceramics containing apatite-wollastonite (designated A.W-GC) were used. In the second experiment, plates (15 x 10 x 2 mm) of A.W-GC and its parent glass (designated G) were used. In each experiment, two paired specimens of identical material, one tied with silk thread, the other not tied, were implanted subcutaneously into rats. In both experiments, bonding to each other of both tied and untied specimens was observed one month after implantation. A pattern resembling hydroxyapatite was identified on the detached surface of the bonded A.W-GC by micro-beam x-ray diffraction. The weak crystalline pattern was also observed on the detached surface of bonded G samples. Analysis of the interface by SEM-EPMA showed that a calcium-phosphorus rich layer formed between the two bonded surfaces in both experiments. It is suggested that the bonding between the two materials was formed by the calcium-phosphorus rich layer, and that the calcium-phosphorus rich layer is virtually identical to hydroxyapatite.
 ...
PMID:Analysis of A.W glass-ceramic surface by micro-beam x-ray diffraction. 215 98

The reactivity of various refractory oxides (SiO2, Al2O3, MgO, CaO, ZrO2) with molten titanium was investigated by energy dispersive X-ray spectroscopy (EDS), using single crystals of oxide as specimen. The region of the reaction boundary between titanium and single crystal oxide was observed by electron microscopy (SEM). Elemental analysis across the Ti/oxide boundary was done by EDS and the reaction layer thickness was quantitatively determined. Of these refractory oxides, SiO2 is the most reactive with titanium followed by Al2O3. The 250 microns thick Si-rich region and 100 microns thick Al-rich region were formed respectively in Ti around the remnant oxides. The diffusion of Si as a result of reaction is greater than that of Al. MgO, CaO, ZrO2 show very little reaction with Ti and the reaction layer thickness was below the spatial resolution of EDS (approximately 1 micron). The thickness and composition of the reaction layer and reactivity were determined. These results were in good agreement with those obtained by ESCA.
 ...
PMID:[High temperature reactivity between titanium and refractory oxides in dental casting procedure. Fundamental study on refractoriness of investments and ceramo-metal bonding by analytical SEM and oxide single crystals]. 269 Mar 91

In this study, it was found that a Ca-P layer and a Si layer were formed on the interface of the mother glass of apatite-wollastonite containing glass-ceramics (designated AW) and bone tissue. The dissolution of Si, Ca, and P from glass (MgO-CaO-SiO2-P2O5-CaF2) is necessary to form a chemical film (a Si layer and a Ca-P layer). The three kinds of glasses used were 1) a mirror surface of the mother glass (MgO 4.6, CaO 44.9, SiO2 34.2, P2O5 16.3, CaF 0.5 weight ratio) of AW (designated G-AW (mirror], 2) an abraded surface of G-AW (designated G-AW (#2000)), 3) a mirror surface SiO2 glass (designated G-Si, 100% SiO2). The glass plates (15 mm x 10 mm x 2 mm) were implanted into the metaphysis of tibia of mature male rabbits for 10 and 25 weeks. The failure load, when an implant detached from the bone or when the bone itself broke, was measured by a detaching test and the interface of glass/bone was observed by SEM-EPMA. Failure loads in G-Si, G-AW (mirror), and G-AW (#2000) 10 weeks after implantation were 0.18 +/- 0.24, 3.06 +/- 1.29, and 2.94 +/- 1.77 kg, respectively. Those in G-Si, G-AW (mirror), and G-AW (#2000) 25 weeks after implantation were 1.30 +/- 1.18, 3.88 +/- 1.06, and 3.55 +/- 1.51, respectively. The failure loads in G-Si vs. G-AW (mirror) and those in G-Si vs. G-AW (#2000) differed significantly (P less than 0.01). There were no significant differences in the failure load according to the surface roughness of G-AW. As shown by SEM-EPMA observation, a Si layer next to G was adjacent to a Ca-P layer next to the bone. The chemical film showed no increase in thickness as time passed. A Ca-P layer did not form on the interface of Si-G and bone.
 ...
PMID:Bone bonding behavior of MgO-CaO-SiO2-P2O5-CaF2 glass (mother glass of A.W-glass-ceramics). 273 79

The progressive changes of a Ca-P-rich layer between bone and three types of apatite-containing glass-ceramics of the same chemical composition: MgO 4.6, CaO 44.9, SiO2 34.2, P2O5 16.3, CaF2 0.5 (in weight ratio) were examined. Plates (15 mm X 10 mm X 2 mm, mirror surface) containing apatite (35 wt%) (designated A-GC), apatite (35 wt%) and wollastonite (40 wt%) (designated A.W-GC), and apatite (20 wt%), wollastonite (55 wt%), and whitlockite (15 wt%) (designated A.W.CP-GC) were prepared. They were implanted into the tibia of mature male rabbits for 5 days, 10 days, 20 days, 30 days, 60 days, 6 months, and 12 months. All three types of glass-ceramics showed direct bonding to the bone 30 days after implantation. It was observed by SEM-EPMA 30 days after implantation that Si and Mg content decreased, P content increased, and Ca content did not change across the reactive zone from the glass-ceramics to bone. The level of P and Si in the A.W.CP-GC changed five days after implantation. In A.W-GC and A-GC, a little change in P and Si levels was observed between 10 and 20 days after implantation. The width of reactive zone was narrowest with A-GC, wider with A.W-GC, and widest with A.W.CP-GC. The dissolution of glass-ceramics stopped 6 months after implantation. This phenomenon shows that the glass-ceramics may be suitable for clinical use.
 ...
PMID:SEM-EPMA observation of three types of apatite-containing glass-ceramics implanted in bone: the variance of a Ca-P-rich layer. 369 88

We have produced three kinds of apatite-containing glass ceramics of the same chemical composition: MgO (4.6), CaO (44.9), SiO2 (34.2), P2O5 (16.3), CaF2 (0.5) (in weight ratio). They contain different crystal combinations and have different mechanical properties. The first glass ceramic (A-GC) was prepared by heating a glass plate to 870 degrees C. It contains only oxy- and fluoroapatite (35 wt%). The second glass ceramic (A-W-GC), and the third (A-W-CP-GC), were prepared by heating glass powder compacts to 1050 degrees C and 1200 degrees C, respectively. A-W-GC contains oxyapatite and fluoroapatite (Ca10(PO4)6(O,F2] (35 wt%) and beta-wollastonite (40 wt%). A-W-CP-GC contains oxyapatite and fluoroapatite (20 wt%), beta-wollastonite (CaO X SiO2) (55 wt%), and beta-whitlockite (3CaO X P2O5) (15 wt%). The bending strengths of A-GC, A-W-GC, and A-W-CP-GC were 88MPa, 178MPa, and 213MPa, respectively, in air. Rectangular ceramic plates (15mm X 10mm X 2mm) were implanted into a rabbit tibia. Ten and 25 weeks after implantation, the segment of tibia with implant was excised for examination. The segment was held by a special jig and the traction breaking load (failure load) was measured by an autograph. A-GC showed a lower load than A-W-GC and A-W-CP-GC. The loads for A-W-GC and A-W-CP-GC were almost equal. The failure loads did not change significantly between 10 and 25 weeks for any of the materials. The interface was examined by Giemsa surface staining, contact micro-radiography, and SEM-EPMA. Giemsa surface staining and CMR revealed direct bonding between the materials and the bone for all the three materials. SEM-EPMA showed that Si and Mg content decreased, Ca content did not change, and P content increased at the reaction zone between all three glass ceramics and bone. This was observed at 10 weeks, as well as at 25 weeks, after implantation. The reaction zone was narrowest with A-GC, wider with A-W-GC, and widest with A-W-CP-GC.
 ...
PMID:Bone bonding behavior of three kinds of apatite containing glass ceramics. 378 83

There is extensive experimental and surgical experience with the use of bone tissue to fill defects in the skeleton, to bridge non-union sites, and to pack defects in bone created from cyst curettage. DP-bioactive glass with a chemical composition of Na2O 8.4%, SiO2 39.6%, P2O5 12% and CaO 40% has been reported as an alternative bone substitute of high mechanical strength, good biocompatibility. and which has a tight bond with living tissue. The bonding layer between DP-bioactive glass and bone tissue was considered to be formed by dissolution of calcium and phosphate ions from the DP-bioactive glass into the surrounding body fluids. The biological hydroxyapatite was suspected to deposit directly onto the bonding layer. In order to confirm the interaction between the DP-bioactive glass and bone tissue, the developed bioactive glass was implanted into rabbit femur condyle for 2-32 weeks. The histological evaluation of DP-bioactive glass as a bone substitute was also investigated in the study. Porous hydroxyapatite bioceramic was used in the control group and the results were compared with those of DP-bioactive glass. The interface between the DP-bioactive glass and bone tissue examined with SEM-EPMA showed that the bioactive glass formed a reaction layer on the surface within 2 weeks after operation and formed a direct bond with natural bone. The elements contained in the bioactive glass apparently interdiffuse with the living bone and biological hydroxyapatite deposited onto the diffusion area, which was proved by EPMA and TEM. After implantation for over 8 weeks, the DP-bioactive glass was gradually biodegraded and absorbed by the living bone. Histological examination using the optical microscope showed that osteocytes grow into the inside of the DP-bioactive glass and the bioactive glass would be expected to be a part of bone.
 ...
PMID:Sintered porous DP-bioactive glass and hydroxyapatite as bone substitute. 788 80


1 2 3 4 5 6 7 8 9 10 Next >>