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Biomedical subjects

K Debari

Publications and source records attributed to K Debari.

32 records · Page 2Linked to original sources
PubMed1992

Application of the environmental SEM in human dentin bleached with hydrogen peroxide in vitro.

The environmental SEM (E-SEM) can be used unfixed biological samples under a low vacuum and wet condition. In this study, the fractured dentin of unfixed human teeth was treated with a 30% hydrogen peroxide solution (H2O2) for the examination of tooth-bleaching prior to the E-SEM and a conventional SEM. The peritubular matrix (PM) always showed a few cracks along the long axis of a dentinal tubule, and the ends of fine fibrils rose to the smoothly changed surface of the intertubular matrix (IM). The E-SEM with non-fixation and the conventional SEM following fixation indicated that the hydrogen peroxide solution easily permeated the PM and dissolved the non-fibrillar substance including the cracks of the PM by the constriction. In the IM, the solution may partially dissolve the organic parts within mineralized fibrils as well as non-fibrillar substance between the fibrils, although these remnants might precipitate again there.

Adolescent↗
PubMed1991

Physico-chemical and morphological studies of horse dentin.

The well-developed thick peritubular matrix (PM) in the middle layer of horse dentin was physico-chemically and also morphologically compared with the intertubular matrix (IM) and the enamel using several microscopes. In scanning laser microscopy, the PM showed a higher laser-beam reflection than the IM, and the contrast image was similar to that of the backscattered electrons by SEM, but to be lower than that of X-ray opacity in microradiography. By SEM-EDX, Ca, P, and Mg were detected from the PM and IM. The mineral content of the PM composed of 15-20 nm sandygrain-shaped crystallites under SEM was significantly higher than that of the IM, but lower than the enamel. The PM/IM in each Ca and P content by weight showed a low average of 1.11, which corresponded to that of their specific gravities previously reported. In Vickers hardness tests, the PM was significantly harder than the IM but softer than the enamel. The PM/IM in the microhardness number showed a high average of 1.85.

Animals↗
PubMed1991

Heterogeneity of crystals attached to the human enamel and cementum surfaces after calculus removal in vitro.

Twenty one extracted human teeth with dental calculi on the enamel and cementum surfaces, fixed in 10% neutral formaldehyde, were selected for this study. After ethanol dehydration and air drying, these calculi were removed by tweezers to observe the teeth surfaces under them. The inspection of these surfaces using SEM and EDX revealed hexahedrally based crystals including pseudocuboidal, rhombohedral and variable rugged rocky shapes. These crystals were identified as Mg-containing whitlockite. The pseudocuboidal crystals, measuring about 4.5 microns in maximum length, were widely distributed on the cervical enamel surface previously covered by calculus. On the root surface, however, these areas decreased remarkably; the shapes changed from pseudocubes into rhombohedrons and rugged rocky structures, while their sizes were smaller and the Mg content decreased. The difference in frequency and morphological variation of the hexahedrally based crystals might be caused by the different characteristics of enamel and cementum surfaces and the Mg present on these surfaces.

Calcium Phosphates↗
PubMed1991

Mineral content of the innermost enamel in erupted human teeth.

It has been said that the innermost enamel of erupted human teeth is either a hyper- or a hypomineralized layer. Using SEM-EDX, in the present study, the Ca and P mineral contents of the innermost 10-15 microns enamel showing a highly negative birefringence (IE-I) were analyzed and compared with those of the adjacent inner enamel (IE-II) in each cuspal-third, mid-coronal, and cervical-third region. The Ca content in the IE-I zone was significantly lower than that in the IE-II zone in the mid-coronal and cervical-third regions, whereas the significant difference of P content was seen only in the cervical-third region. In the other areas, the IE-I zone tended to be lower than the IE-II zone. These significant and no significant differences of Ca and P contents may be due to the difference in the amount of organic substance in the IE-II zone of the three regions, and that of these mineralization rates after eruption of a tooth.

Adolescent↗
PubMed1990

Possible role of cementoblasts in the resorbant organ of human deciduous teeth during root resorption.

Human deciduous teeth undergoing physiologic root resorption were extracted and fixed with a mixture of formaldehyde and glutaraldehyde and processed for scanning (SEM) and transmission (TEM) electron microscopy, and for acid (ACPase) and alkaline phosphatase (ALPase) cytochemistry. The resorbant organ, rich in odontoclasts, cementoblasts, fibroblasts, and macrophages, formed prominent resorption lacunae in root dentin. SEM observations of resorption lacunae treated with trypsin solution showed islands of newly-formed cementum matrix in part of the resorbing dentin surfaces. Such cementum consisted of bundles of densely-arranged collagen fibrils and, in part, contained forming cementocytic lacunae and canaliculi. Active cementoblasts adjacent to odontoclasts on resorbing dentin surfaces showed cuboidal outlines and were characterized by the presence of numerous cisterns of rough endoplasmic reticulum, well-developed Golgi complexes, secretion granules, and many mitochondria. They sometimes formed a thin layer of cementoid and/or cementum matrix upon the resorbing dentin surface. These cementoblasts had ACPase-positive lysosomes in the cell bodies and exhibited intense ALPase activity along the plasma membranes of whole cell surfaces. These results suggest that, during root resorption, 1) active cementoblasts are present adjacent to active odontoclasts and 2) these cementoblasts are involved in remodeling the resorbing dentin surfaces.

Acid Phosphatase↗
PubMed1989

Prostaglandins promote osteoclastlike cell formation by a mechanism involving cyclic adenosine 3',5'-monophosphate in mouse bone marrow cell cultures.

We have developed a mouse bone marrow culture system in which multinucleated osteoclast (OC)-like cells are formed within 8 days. Using this culture system, we examined the effect of prostaglandins (PGs), potent bone-resorbing agents, on OC-like cell formation. Four PGs (PGE1 and PGE2 at 10(-8)-10(-5) M, 6-keto-PGF1 alpha at 10(-5) M, and PGF2 alpha at 10(-6)-10(-5) M) significantly stimulated the formation of OC-like cells. The potency of the PGs in inducing OC-like cell formation was the highest in PGE1 and PGE2, followed by PGF2 alpha and 6-keto-PGF1 alpha in that order, and the order was highly correlated with the order of the potency in increasing the production of cyclic adenosine 3',5'-monophosphate (cAMP) in bone marrow cells. Addition of dibutyryl-cAMP also induced OC-like cell formation. Moreover, isobutylmethylxanthine (IBMX), a potent inhibitor of phosphodiesterase, potentiated the OC-like cell formation induced by PGE2, whereas salmon calcitonin greatly inhibited it. Calcitonin induced cAMP production in cultures treated with PGE2, but not in cultures with vehicle. When bone marrow mononuclear cells were cultured on dentine slices in the presence of PGE2, multinucleated OC-like cells were similarly formed and they resorbed calcified dentine, resulting in so-called Howship's lacunae. These results suggest that PGs stimulate resorption of calcified tissues by promoting osteoclast formation. The activity of PGs in inducing OC-like cell formation is considered mediated mainly by a mechanism involving cAMP.

Animals↗
PubMed1987

Ameloblast modulation and changes in the Ca, P, and S content of developing enamel matrix as revealed by SEM-EDX.

Freeze-dried rat incisors were examined by high-resolution scanning electron microscopy (SEM) combined with energy-dispersive x-ray microanalysis (EDX) for determination of the correlation between the morphology of the enamel organ and the concentrations in the adjacent developing enamel matrix of calcium (Ca), phosphorus (P), and sulfur (S), as well as the Ca/P ratio. In SEM examination of the freeze-dried enamel organ, it was possible to identify the stages of enamel secretion, transition, and maturation, and furthermore to identify ruffle-ended and smooth-ended maturation ameloblasts. EDX analysis of the outer layer of forming and maturing enamel was carried out from the apical to the incisal end at interval points of approximately 50 micron. Ca and P concentrations increased gradually and continuously from the secretion zone to the end of the maturation zone, but never showed a steep rise in any of the zones examined. Maturing enamel overlaid by either ruffle-ended or smooth-ended maturation ameloblasts showed similar Ca and P concentrations. Throughout the outer enamel layer, the Ca/P molar ratio was fairly constant. Sulfur concentration began to decrease in the zone of enamel secretion, and was no longer detected in the middle of the maturation zone.

Ameloblasts↗
PubMed1986

Correlated observations and analysis of maturation-ameloblast morphology and enamel mineralization.

A combined HCl-collagenase digestion technique and scanning electron microscopy were used to isolate the enamel organ and to confirm the presence of maturation ameloblasts of both ruffle-ended (RA) and smooth-ended (SA) types on maturing enamel in kitten permanent tooth germs. EDTA perfusion of animals fixed with aldehyde produced two or three belt-like shallow grooves (from 30 to 100 micron wide) running horizontally through the maturing enamel surface, coinciding closely with the SA distribution pattern. In animals that had been perfusion-fixed with unbuffered osmium tetroxide containing 2.5% potassium pyroantimonate, SEM-EDX analysis detected K in a superficial enamel layer overlaid by the SA layer. Potassium concentration decreased gradually toward the deeper layers. Very little K penetrated the enamel under the RA layer. Energy-dispersive x-ray analysis of Ca and P concentrations in the enamel revealed an even distribution of these elements throughout the superficial layer of maturing enamel. These results suggest that the SA layer forms an access route for K and EDTA and that, in spite of the obvious morphological and functional differences between RA and SA, the maturing enamel surfaces overlaid by these two cell types show similar degrees of mineralization.

Ameloblasts↗
PubMed1984

Energy-dispersive X-ray microanalysis and scanning electron microscopy of developing and mature cat enamel.

Calcium and phosphorus distribution in forming, maturing and mature enamel of cat teeth and the microstructures manifest in all these were examined in fractured enamel from the dentine-enamel junction toward the enamel surface. concentrations of both Ca and P increased gradually from the forming enamel, through the maturing enamel and into the mature enamel. The innermost layer, adjacent to the dentine-enamel junction showed the greatest and the superficial layer the lowest concentration of Ca. Still the mature enamel of the erupted tooth was not yet completely mineralized and Ca and P concentrations only slightly higher than those in maturing enamel. Molar Ca:P ratio of each enamel stage was lower than that of pure crystalline hydroxyapatite. Simultaneously-performed SEM observations revealed microstructural changes in the enamel: in the forming-front layer of the forming enamel, the enamel was a rough, immature structure but began to show more compact, tighter structures as concentrations of Ca and P altered. The results suggest that the enamel organ exercises intense cellular control over increases of Ca and P concentration during the formation and maturation stages of amelogenesis.

Amelogenesis↗