PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “APATITES”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 955 records · Page 53Linked to original sources
PubMed1981

High resolution electron microscopic technique applied to the detection of distortions in apatite crystallites during amelogenesis.

Distortions in the crystal structure of developing tooth enamel from human fetuses and newborn cats were studied by high resolution electron microscopy. Undecalcified sections were observed in a JEOL 100B transmission electron microscope. Two kinds of crystal sections were observed. In one, the diffraction images corresponded to the (10.0) and (00.2) lattice planes, and in the other they corresponded to the (01.0) and (10.1) planes. The unit cell distortion in naturally bent crystals showed a linear correlation with the inverse of the radius of curvature for both the [00.2] and the [10.1] axes. along the [00.2] axis of crystallites from both cat and human enamel, the distortion per unit cell was linearly correlated with the inverse of the length of the crystallite segment under consideration.

Amelogenesis↗
PubMed1993

Observations of structural features and characteristics of biological apatite crystals. 3. Observation on ultrastructure of human dentin crystals.

In a series of studies to investigate the structural features of the biological crystals, using electron microscope, we examined the ultrastructure of the human dentin crystals at near atomic resolution through the cross and longitudinal sections of the crystals. The materials used for this study were the deep layer of the non-carious coronal dentin from freshly extracted human erupted permanent molars. The small cubes of the dentin were fixed in glutaraldehyde and osmium tetroxide and embedded in epoxy resin using the routine methods. The ultrathin sections were cut with a diamond knife without decalcification. The sections were examined with the HITACH H-700 type of transmission electron microscope operated at 200kV. Each crystal was observed at the initial magnification of 300,000 times and at the final magnification of 10,000,000 times and over. Using this approach, the authors have been able to show the configuration of the hydroxyapatite structure in the cross and longitudinal sections of the dentin crystals deposited within and between the collagen fibrils (intrafibrillar and interfibrillar crystal) in the intertubular dentin and observe the basic hexagonal pattern of the unit cell viewed down the c-axis. The authors sincerely believe that the electron micrograph shown in this report is the first atomic image to be obtained from a hydroxyapatite crystal from the human dentin, using the sections.

Apatites↗
PubMed1996

Apatite deposition in polymyositis subluxing arthropathy.

We describe a 47-year-old woman who developed chronic subluxing arthropathy associated with polymyositis (PM) and positive anti-Jo1 antibodies. After a followup of 3 years, PM did not recur and polyarthritis dominated her clinical picture, leading to deformities and periarticular calcifications in her hands, shoulders, and feet. Patients with myositis, anti-Jo1 antibodies, and periarticular calcifications are at risk of developing deforming arthritis unresponsive to conventional therapy.

Adult↗
PubMed1988

Mineralization and calcium fixation within a porous apatitic ceramic material after implantation in the femur of rabbits.

Cylinders (0.8 cm long, 1.0 cm of diameter and with an axial hole), constituted, after firing, of a ceramic mixture of hydroxylapatite (HA) and beta-tricalciumphosphate (beta-TCP) in a 10:1 ratio, were implanted into mid-diaphyseal defects of one femur of 20 rabbits and stabilized with intramedullary rods. The implantation sites were checked radiographically every month, and after 3 months (3 animals) and 6 months (17 animals) the rabbits were sacrificed and the implants with the surrounding tissue were embedded in methylmethacrylate, cut to thick sections and analyzed by scanning electron microscopy (SEM). Porosimetric and x-rays diffraction analyses were carried out before and after implantation of the cylinders, and the state of mineralization at the bone-implant interface was determined by EDAX microprobe analysis. Bony callus formation started at 1 month at the osteotomy sites, as judged by radiography, but after 3 months a not-mineralized zone had still been demonstrated between bone and the implants. At 6 months, 13 implants showed themselves firmly fixed in their implantations beds, while 4 implants were only incorporated at their proximal ends. In bone contact zones, an enrichment of Ca2+ was displayed by microanalytical techniques in the outer zone of the implanted samples which may be explained by an apparent additional phase transformation of HA into TCP, thanks to the change of the Ca/P ratio, that takes place in vivo.

Animals↗
PubMed1989

Desorption and exchange properties of adsorbed albumin on apatite. Influence of long-term interfacial residence times.

A technique using 125I-labeled proteins was employed to study static adsorption properties and slow exchange and desorption processes of human albumin in contact with synthetic hydroxyapatite beads. With the aid of a thermostated "minicolumn," the adsorption isotherm was obtained during a so-called multiadsorption process, and could be described by a Langmuir adsorption model (K = 1.10 x 10(10) cm3.mol-1). All kinetic desorption and exchange experiments could be fitted by a simple exponential function of time. No influence of long-term interfacial residence times on characteristic relaxation times or percentage of desorbed or exchanged proteins could be detected in the present system. On the other hand, as compared to the low surface coverage domain, the small percentage of desorbable and high percentage of exchangeable molecules in the adsorption plateau domain was attributed to a bimolecular exchange process.

Adsorption↗
PubMed1989

Inhibition of apatite formation by titanium and vanadium ions.

Ti4+ and V5+ ions were studied in two biologically relevant in vitro test systems to determine their effect on hydroxyapatite (HA) formation. System 1 involved direct HA precipitation from solution, and system 2 dealt with the growth of HA seed crystals. The experiments were carried out in a pH-stat by continuously recording NaOH uptake, which follows HA formation kinetics, at pH 7.4, 37 degrees C, and 0.15 M NaCl. In systems 1 and 2, Ti decreased HA formation kinetics in a dose-related manner without delaying the onset of HA formation. For V, the rate of HA proliferation decreased in system 1 in a dose-related manner, but the curves displayed a complicated shape. In system 2, V brought about a decrease in the HA seeded growth rate. Previous work has shown that Al blocks HA proliferation by adsorbing to active growth sites on the surface of HA crystals. By contrast, in this study V was found not to be adsorbed to the surface of HA. The mechanism of action of V probably involves the poorly understood hydrolysis and solution complex formation chemistry of the metal ion. We have shown here that V ions form V-PO4 complexes in solution in the HA formation systems; undoubtedly these are involved in the mechanism of V inhibition of HA formation. On the other hand, Ti was shown to bind to the surface of HA crystals in this study, which means that the ion may poison active crystal growth sites, as does aluminum. Ti-6Al-4V alloy is widely used in cementless total hip implants. Previous studies have shown that Ti concentrations 10 to 100 times higher than used here accumulate in osseous tissues around porous Ti implants in dogs 6 to 12 months after implantation. Ions leaching out over long periods of time into the implant interface could interfere with the normal osteoid mineralization and remodeling processes of bone in that region, which would result in subsequent loosening of the implant. This research suggests that further in vitro and animal studies should be carried out to determine the extent of Ti and V ion leaching from implants and their effect on tissue mineralization.

Chemical Phenomena↗
PubMed1991

Plasma-sprayed coatings of tetracalciumphosphate, hydroxyl-apatite, and alpha-TCP on titanium alloy: an interface study.

In order to study the interaction of calcium phosphate coatings with bone tissue, coated titanium cylinders with a standard size were implanted in dog femora. Coatings were made by plasma spraying powders of hydroxylapatite, beta-whitlockite, and tetracalciumphosphate particles. The plasma spraying process turns beta-whitlockite into alpha-TCP. Bone bonding and bone formation were evaluated by mechanical push-out tests and histological observations. Hydroxylapatite and tetracalciumphosphate coatings show an interface strength after 3 months of implantation of 34.3 +/- 6.5 MPa and 26.8 +/- 3.9 MPa, respectively, while alpha-TCP and blanco titanium lead to an interface strength of 10.0 +/- 3.5 MPa and 9.7 +/- 1.3 MPa, respectively. Histological examinations revealed that hydroxylapatite and tetracalciumphosphate give rise to an excellent bone formation, while alpha-TCP and blanco titanium evoked remodeling and less bone contact.

Alloys↗