Randi Furseth

The resorption processes of human deciduous teeth studied by light microscopy, microradiography and electron microscopy.

Abstract Forty-four deciduous human teeth were used in this study of the resorption processes by means of light microscopy, microradiography and electron microscopy. Particular emphasis was placed on the fine structure of the tooth/soft tissue interface. Generally, resorption was found to be most advanced in the apical areas, and in the molars it also occurred in the bifurcations and trifurcations. In addition, resorption lacunae were observed in other areas of the root surface, in the root canals, and occasionally in the pulp chamber. The hard tissue had a “honeycomb” appearance in areas where resorption was taking place or had occurred. Odontoclasts (multinucleated cells) were found both on the tooth surface and in its immediate surroundings. The most conspicuous features of these cells were a large number of mitochondria, vacuoles and free ribosomes, while the endoplasmic reticulum was scarce. Where the odontoclast was in contact with the tooth surface, a system of canals extending 2–3 μ into the cytoplasm was observed, and these canals contained mineral crystals. The tooth surface in this area showed a zone of decreased mineral content approximately 1 μ wide. The regularly observed repair tissue resembled cellular cementum in structure. It was separated from the underlying tissue by a reversal line, which could be demonstrated in the light microscope as well as in the electron micrographs. Cementoblasts (hard tissue-forming cells) were characterized by a rich, rough-surfaced endoplasmic reticulum and a large number of mitochondria. The precementum zone of repair tissue was approximately 15 μ in width, and thus was wider than that reported for regular cementum formation. Calcific globules were observed in the precementum, the crystals on the surface of the repair tissue appeared smaller than those deeper in the tissue, and the newly mineralized tissue did not seem as electron dense as the older tissue.

Further observations on the fine structure of orally exposed and carious human dental cementum.

Abstract Exposed non-carious cementum often exhibited an X-ray dense surface layer containing tablet-shaped crystals which gave the diffraction pattern of hydroxyapatite. PTA-demineralized sections showed the crossbanding typical for collagen in some of these specimens, while in others the crossbanding was diffuse. In some specimens, the crystals in the surface layer seemed more resistant to PTA-demineralization than the crystals deeper in the tissue. Some of the specimens showed small calculus deposits on the surface. The carious cementum had an uneven surface with tablet-shaped crystals with the diffraction pattern of hydroxyapatite in the surface layer. PTA-demineralized sections showed the crossbanding of the collagen fibres close to the bacterial plaque, but a splitting of fibres were often noted in the surface layer. In specimens which microradiographically had a brush-like appearance, spikes of cementum with a high mineral content alternated with areas filled with bacteria. In subsurface areas smaller and larger areas devoid of mineral as well as a marked depletion of crystals were noted. In demineralized sections distinct crossbanding of the fibres, areas with diffuse crossbanding as well as areas with fibres with a reticular appearance were observed. In one specimen of carious cellular cementum, collections of large, electron-dense crystals with an irregular rhombohedral shape alternated with areas occupied by bacteria as well as areas occupied by thin, rod-shaped crystals up to 2500A in length. The rodshaped crystals gave the diffraction pattern of hydroxypatite and had a collagenous matrix, while the large, electron-dense crystals gave the diffraction pattern of whitlockite and upon demineralization showed absence of organic matrix.

The fine structure of the cellular cementum of young human teeth

Abstract The fine structure of cellular cementum from the apical portion of young human teeth has been studied, with emphasis on the cellular component. The cementoblasts exhibited the cytologic features typical of cells actively synthesizing proteins. In one instance a cilium, surrounded by a circumciliary invagination of the cell membrane, was seen. The width of the precementum varied, but was approximately 5 μ. Cells located in the precementum showed cytologic features similar to the cementoblasts, while the cementocytes embedded in the calcified matrix contained fewer organelles than the cementoblasts. In some specimens large unmineralized areas were observed close to the cementodentinal junction, some containing a cellular component in the plane of section. These cells had a fairly rich endoplasmic reticulum and numerous mitochondria, indicating that they had a higher degree of activity than the cementocytes in the lacunae. In a few instances unmineralized areas containing two cells were observed and, in one instance, tight junctions were seen between the cells. The walls of the lacunae and the unmineralized areas seemed to have the same electron density as the surrounding tissue.

The inorganic phase of calcium hydroxide—and corticosteroid-covered dentine studied by electron microscopy

Abstract Undecalcified, ultrathin sections of human dentine dissected out from dry, ground sections of Ca(OH)2-covered, corticosteroid-covered and normal dentine have been studied. The localized increase in mineralization of the dentine following the insertion of experimental restorations in vivo, using the two compounds as liners, was found to be caused by an intratubular deposition of minerals. In Ca(OH)2- covered dentine the obturation of the tubules consisted of a moderately electron dense, crystalline material. In corticosteroid-covered dentine irregularly shaped tubules were observed close to the predentine and many tubules were obliterated by a highly electron dense material.

Ultrastructure of tissue in intrabony and subperiosteal porous ceramic implants

Porous ceramic (Al2O3) implants with pore size of 100--750 micron were placed intrabony in the maxilla and subperiosteally in the mandible of three adult monkeys. After observation periods of 10, 11 and 12 months, the animals were perfused with 1.7% glutaraldehyde and the jaws processed for electron microscopy. Tissue ingrowth into the pores was observed in all the specimens. The implant pores facing the host bone contained bone tissue to a depth of approximately 1 mm, while only unmineralized tissue was found in the implant part adjacent to the periosteum. The unmineralized tissue was of a fibrous nature with collagen fibers arranged in a lamellar fashion. Cells, often with extremely long and slender cellular processes, were seen between the lamellae. The cells had the cytoplasmic features typical of protein-producing cells. The mineralized tissue exhibited ordinary bone tissue structure with plate-like crystallites in a collagenous matrix. Some lacunae and canaliculi with osteocytes were observed, though they were scarce.

The occurrence of atypical crystals in human cellular cementum fixed in phosphate-buffered fixatives

Abstract In some specimens of cellular cementum, atypical crystals were observed around the circumference of some of the lacunae and the large unmineralized areas close to the cemento-dentinal junction. These crystals were only observed in the specimens fixed in phosphate-buffered fixatives, and not in specimens fixed in cacodylate buffered fixatives. The number varied from a few scattered crystals to a zone 3–4 μ in width. The crystals appeared as electron-dense rods or needles and as less electron-dense plates of varying size. The largest were mostly between 1500 and 2000A in length and were thus considerably larger than the ordinary crystals of cementum. These large crystals were considered to be artifacts brought about by the phosphate ions in the fixative which might have caused precipitation in areas of high calcium concentration. In one specimen intracellular electron-dense deposits were observed in several of the cementocytes and in cells in the unmineralized areas. The possible nature of the deposits is discussed.

The fine structure of corticosteroid-covered, human dentine.

Abstract Cavities were prepared in intact young premolars and restored with amalgam using a corticosteroid preparation as a liner. The teeth were extracted after observation periods varying from 17 to 138 days and processed for electron microscopy. In teeth with observation periods exceeding 20 days, the width of predentine was reduced or absent corresponding to the cavity tubules. A reduction both in the size and number of the odontoblasts was also noted. Partly or completely obturated dentinal tubules were often observed. The partly obturated tubules showed eccentric growths of mineralized tissue. Unmineralized collagen fibres were often seen in the peri-odontoblastic space, indicating that collagen is a large part of the organic matrix in the obturated tubules. In some of the odontoblast processes, an unusually large number of mitochondria and endoplasmic reticulum were observed.

Concentration of rare earths in dentine and enamel: A pilot study

A neutron activation method for the determination of rare earths in hard tissues was developed and the concentrations of some of these elements in human dentine and enamel were determined. The results obtained for La, Sm, Tb and Yb are very low, indicating a total rare-earth content of the order of 0.1 ppm or less in the samples investigated. The observed La/Sm ratios seem to indicate a slight enrichment of the lighter rare earths relative to the heavier, as compared to average geological abundances.

The fine structure of induced pulpitis in a monkey (Cercopithecus aethiops)

Abstract Human carious dentine was sealed with amalgam in five deep cavities prepared in intact teeth and left in place for 7 days to develop pulp inflammation. The monkey was anaesthetized, and perfused with glutaraldehyde. Transmission electron microscopy of sections showed that in four teeth the odontoblast layer was hardly recognizable being largely replaced by polymorphonuclear leucocytes, which were also observed in the dentinal tubules of both predentine and dentine. The width of predentine was reduced and the mineralization front was uneven. Necrotic changes including the presence of numerous bacteria and remnants of cells and fibres in the pulp, predentine and dentinal tubules affected the fifth tooth. The mineralization front was very irregular and the narrow predentine contained few fibres.

Pulp studies after 2 per cent sodium fluoride treatment of experimentally prepared cavities.

Abstract The pulpal response to 2 per cent sodium fluoride (NaF) applied for 2 minutes in twenty experimentally prepared cavities in young human teeth was studied after observation periods varying from 7 to 108 days. In some of the teeth the pulp was unaltered subjacent to the cavity tubules, and in the others only minor changes were observed, including an obscuration of the cell-free zone. In two cavities observed for long periods, in which the remaining dentin was extremely thin, the predentin layer was wider than normal and the odontoblast layer was reduced in width.