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J C Barry

Publications and source records attributed to J C Barry.

39 records · Page 3Linked to original sources
PubMed1985

High-resolution electron microscope and computed images of human tooth enamel crystals.

The structure of human enamel crystallites has been studied at a near atomic level by high-resolution electron microscopy. Electron micrographs have been obtained from crystallites present in human enamel with a structure resolution of 0.2 nm in the [0001], [1210], [1213], [1100] and [4510] zone axes directions. In most cases it was possible to match the experimental images with images calculated using the atomic positions of mineral hydroxyapatite. However, in some cases a discrepancy between calculated and experimental image detail was observed in the c direction of the [1210] and the [1100] images. This shows: (i) a structural heterogeneity of the crystals, and (ii) a loss of hexagonal symmetry of the structure. The resolution required to distinguish individual atomic sites in the different zones has been determined, and this will provide a useful basis for future work. As the determination of the "real structure" of biological crystals is of prime importance for the study of calcification mechanisms (crystal growth), biological properties and destructive phenomena of calcified tissues (i.e., dental caries and bone resorption).

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The evolution of stability in cervical spinal constructs using either autogenous bone graft or methylmethacrylate cement. A follow-up report on a canine in vivo model.

Thirty-six adult mongrel dogs underwent either a posterior C4-C5 bone graft or methylmethacrylate-cerclage wire construction procedure to simulate the analogous human stabilization procedures. The dogs were divided into groups of six and allowed to live 1, 2, or 3 months after surgery. At the appropriate time they were killed and their C4-C5 spinal segments excised and studied radiologically, mechanically, and histologically. In addition, the C4-C5 spinal segments from 15 other mongrel dogs were excised and either left intact as normal (five) or prepared as one of the two constructs (five each) described above. They were also tested mechanically to provide immediate postoperative stability data. At some time during the first postoperative month the methylmethacrylate constructs lost mechanical stability. In addition, fibrous tissue was noted to have grown between the posterior laminal surface and the cement mass during this same time. Radiologically, loosening was obvious by the second postoperative month. The bone graft constructs were mechanically equivalent to or superior to the normal dogs by the second postoperative month. Likewise, they were well on their way to solid fusion radiologically and histologically by the same time. Impressed by the rapidity of deterioration in mechanical stability for the methylmethacrylate constructs, the authors further questioned their usefulness in cases of traumatic cervical spinal instability. The bone graft constructs continued to appear to be a reliable way to achieve ultimate spinal stability.

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