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OBSERVATIONS ON STRUCTURAL FEATURES AND CHARACTERISTICS OF BIOLOGICAL APATITE CRYSTALS: 9. OBSERVATION ON DISSOLUTION OF CARIOUS ENAMEL CRYSTALS
Get PDFIn a series of studies to investigate the basic structural features and characteristics of the biological apatite crystals using a transmission electron microscope, we examined the ultrastructure of the human enamel, dentin, and bone crystals through the cross and longitudinal sections at near atomic resolution.
Subsequently, using the same approach, we have been able to directly examine the images of the lattice imperfections in the crystal lattices of the human tooth and bone crystals, and the images of the fusion of the crystals.
In this research, furthermore, using transmission and scanning electron microscopes, we examined the dissolution of the enamel crystals caused by the carious enamel from the same viewpoint. The material used for the observation of the dissolution of the enamel crystals was obtained from the region which corresponds to the middle layer of the enamel at the portion near the wall of a carious cavity caused by the fissure caries on the occlusal surface of the lower first molars.
Small cubes of the materials used for the observation by transmission electron microscope were fixed in glutaraldehyde and osmium tetroxide and embedded in epoxy resin using the routine methods. The ultrathin sections we1 e cut with a diamond knife without decalcification. The sections were examined with the HITACHI H-800H type transmission electron microscope operated at 200kV. Each crystal was observed at an initial magnification of 300,000 times and at a final magnification of 10,000,000 times and over.
The material used for the observation by the scanning electron microscope was the fractured surface obtained from the carious enamel. The fractured carious enamel surfaces were coated with carbon and gold and observed with the HITACHI HHS-2R type scanning electron microscope operated at 25kV. The crystals were observed at a final magnification of 50,000 times.
As a result, we have confirmed that the dissolution of the enamel crystals caused by a caries occurs in the units of “hexagonal cell”. We sincerely believe that the electron micrographs shown in this report are the first to show the images of the dissolution of the enamel crystals caused by a caries at near atomic resolution.journal articl
F WAVE CHANGE BY DECREASED MOTONEURONAL EXCITABILITY: A SLEEP STUDY
Get PDFTo clarify the effect of the change in motoneuronal excitability on the F wave, we studied the persistence, mean size, and minimum latency of the F wave in nine normal subjects while awake and asleep. Recordings were made from the abductor pollicis brevis muscle by stimulating the median nerve at the wrist. The persistence and size of the F wave markedly decreased during sleep, especially in stage REM. The mean size in stage REM was less than 5% of that in stage W in most subjects, and the F wave entirely disappeared in one subject. The minimum latency during sleep was longer than during wakefulness. Prolongation was within 2.0 ms when the persistence was more than 10%. A decrease in the number of motoneurons that elicit the F wave may be the major cause of prolongation.
We conclude that the decreased motoneuronal excitability can cause the F wave to disappear without conduction block in the peripheral motor nerve and that the prolongation of the F wave for more than 2 ms provides a marker for proximal conduction delay in the clinical nerve conduction studies.journal articl
OBSERVATIONS ON STRUCTURAL FEATURES AND CHARACTERISTICS OF BIOLOGICAL APATITE CRYSTALS: 5. THREE-DIMENSIONAL OBSERVATION ON ULTRASTRUCTURE OF HUMAN ENAMEL CRYSTALS
Get PDFIn a series of studies to investigate the structural features of the biological crystals, such as the tooth and bone, using an electron microscope, we examined the ultrastructure of the enamel, dentin, and bone crystals at near atomic resolution and showed the configuration of the hydroxyapatite structure through the cross and longitudinal sections of the crystals.
Thereafter, based on the results of the observations by the authors of the ultrastructure of the tooth and bone crystals, thinking that it might be possible to conduct direct three-dimensional observation of the configuration composing the unit cell of the hydroxyapatite crystals, we conducted a study on this. These results indicated that it was possible to sterically observe the configuration of the hydroxyapatite structure composing the enamel crystal.
The materials used for this study were the middle layer of the noncarious enamel from the freshly extracted human erupted permanent molars. The small cubes of the enamel 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 and were examined with the HITACHI H-9000 H type transmission electron microscope operated at 300 kV. Each crystal was observed at an initial magnification of 500,000 times and at the final magnification of 10,000,000 times and over.
We sincerely believe that the electron micrographs shown in this report are the first to show three-dimensionally the configuration of the hydroxyapatite structure composing the crystal in the cross and logitudinal sections of an enamel crystal.journal articl
OBSERVATIONS ON STRUCTURAL FEATURES AND CHARACTERISTICS OF BIOLOGICAL APATITE CRYSTALS: 4. OBSERVATION ON ULTRASTRUCTURE OF HUMAN BONE CRYSTALS
Get PDFIn a series of studies to investigate the structural features of the biological crystals such as the tooth and bone, following the previous observations of the tooth crystal using an electron microscope, we examined the ultrastructure of the human bone crystals at near atomic resolution through the cross and longitudinal sections of the crystals.
The materials used for this study were the normal bone tissue obtained from the buccal alveolar compact bone of the human mandibule in the portion of the lower first molar. The small cubes of the bone tissue 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 HITACHI H-800 type transmission electron microscope operated at 200 kV. 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, we showed the configuration of the hydroxyapatite structure in the cross and longitudinal sections of the bone crystals deposited within and between the collagen fibrils (intrafibrillar and interfibrillar crystals) in the bone tissue.
Furthermore, using the same approach, we observed the crystal lattices of the hydroxyapatite structure appearing in the cross and longitudinal sections. We sincerely believe that the electron micrographs shown in this report are the first atomic images from the section obtained from the hydroxyapatite crystal from the human alveolar bone.journal articl
MECHANICAL PROPERTIES OF ARTIFICIAL TEETH
Get PDFIn selecting the teeth for fabrication of complete or partial dentures, each patient s anatomic and physiologic requirements and the properties of the artificial teeth themselves should be taken into consideration. The purpose of this study was to evaluate the mechanical properties of the artificial teeth by the static compression test and the impact test. Specimens were the lower first molar porcelain and resin teeth (Livdent FB-20 teeth by G.C. Co., Tokyo, Japan). All were of the same shape. In the static compression test, the fracture load and deformation of the artificial teeth were measured with an Instron-type universal testing machine at a cross-head speed of 1.0 mm/min. Elastic modulus, ultimate strength and absorbed energy were calculated. In the impact test, the acceleration of a falling impactor was measured with a drop impact apparatus. The load applied to the specimen was equivalent to 300N. Absorbed energy and deformation were calculated.
The resin teeth showed a lower elastic modulus, higher fracture toughness and shock-absorbing ability than the porcelain teeth. Resin teeth should be selected when the first requisite is high shock absorbing ability, and porcelain teeth should be selected when the first requisite is high masticating efficiency.journal articl
INFLUENCE OF MOLD MATERIALS AND HEAT TREATMENT ON TENSILE PROPERTIES OF Ni-Ti ALLOY CASTINGS
Get PDFThe influence of mold materials and heat treatment on the tensile properties and the transformation temperatures of Ni-Ti alloy castings was investigated by tensile test and differential scanning calorimetry (DSC) in order to apply the special properties of the alloy to dental field. The compositions of the two alloys examined were 49.0 and 49.2 at% Ti. A silica investment and a magnesia investment were used as the mold materials. Heat treatment at 440 °C for 1.8 ks was performed.
Apparent proof strength decreased in both compositions, and residual strain increased in Ni-49.2Ti by the heat treatment. Elongation increased in N i-49.0Ti with use of the magnesia mold or by the heat treatment. The transformation temperatures of Ni-49.2Ti increased with use of the magnesia mold. The change by the heat treatment suggested a structural change. The development of a suitable method for the casting of the alloy is expected to bring about the development of new devices and therapy in dentistry.journal articl
THE LONG TERM DURABILITY OF BOND STRENGTHS TO DENTIN
Get PDFThe aim of this study was to investigate the durability, throughout one year, of tensile bond strengths (TBS) to bovine dentin using various commercial and experimental bonding systems.
Specimens were stored in a controlled solution of ion-exchanged water containing plaster chips and sodium azide.
From the results it was concluded that the changes in TBS were not uniform over time, but a significant decrease was usually observed. For Super Bond D-liner and KB-100, the TBS were the highest and exhibited remarkable stability over the test period.
The mode of fracture was noted to vary depending on the treatment system used, and was independent of TBS. Generally, the fracture mode tended to show increases in adhesive/cohesive failures within the resin over time. Super Bond D-liner always exhibited adhesive type failure at the tooth interface, and later involved failure in the hybrid layer. KB-100 showed very little change in failure over one year, being usually adhesive between bonding resin and resin composite.
The results from this study indicate the need to carry out durability studies for the basic evaluation of all bonding systems. It was shown that the use of a controlled storage solution is important.journal articl
DELETIONAL ANALYSIS OF THE HUMAN RENIN PROMOTER: TRANSCRIPTIONAL ACTIVATION BY THE SV40 ENHANCER ENABLES IDENTIFICATION OF PROMOTER REGULATORY ELEMENTS IN NON-RENIN-EXPRESSING CELLS
Get PDFIdentification of regulatory elements in the human renin gene promoter has been hindered by the lack of suitable renin-expressing cell lines. In this paper, the SV40 viral enhancer is coupled to a human renin promoter/chloramphenicol acetyltransferase (CAT) reporter gene construct, to determine whether promoter regulatory elements can be identified in the context of enhanced transcription in the normally non-renin-expressing HeLa cell line. The present results indicate that the SV40 enhancer can overcome tissue-specificity of the human renin promoter, and confer correctly initiated transcriptional activity to HeLa cells. Analysis of a series of 5’-end deletions of the human renin promoter linked to the CAT gene and SV40 enhancer identified negative regulatory elements between positions-275 and -225, and between -142 and -102 of the human renin promoter, as well as a positive regulatory element between -225 and -142. Thus, studies of renin promoter regulatory elements need not be limited to renin-expressing cells, but can be performed in non-renin-expressing cells with the addition of an enhancer. This strategy can be generally applicable to the study of tissue-specific gene regulation in cases where there are no specific cell lines available.journal articl
ANALYSIS OF IMMUNODOMINANT ANTIGENS OF PORPHYROMONAS GINGIVALIS 381 IN HIGH RESPONDER PATIENTS
Get PDFThe purpose of this study was to determine the immunodominant antigens of P. gingivalis 381 and to examine their composition and molecular weight. Fourteen periodontal patients, with high antibody titers to P. gingivalis 381 sonicated extract, were selected. Whole cell fraction, sonicated extract and outer membrane protein of P. gingivalis 381 were used as antigens in the untreated form as well as in the heated form and treated with papain. Total volume of sugar, protein and lipopolysaccharide (LPS) was estimated in each one of the three antigens. Antibody binding capacity to the three antigens was evaluated, before and after heat and papain treatment, by an enzyme-linked immunosorbent assay (ELISA). In addition, the immunoblotting analysis was performed. The quantitative assays showed that the whole cell fraction contained about ten times more LPS than the other two preparations while the outer membrane protein contained twice the amount of carbohydrates than the other two preparations. The 14 sera were classified into three groups according to the rate of reduction of antibody binding under heat and papain treatment. Concerning heat treatment, most of the sera showed a high reduction of antibody binding when reacting with the sonicated extract. However, antibody binding to the outer membrane protein antigen was hardly decreased by heat treatment in three sera. Also, these three sera showed almost the same response to the whole cell fraction antigen under heat treatment. Under papain treatment, almost all sera showed a moderate reduction of antibody binding when they reacted with the sonicated extract and whole cell fraction while they showed a low reduction of antibody binding when they reacted with the outer membrane protein. From the present study it could be concluded that a main proteinaceous antigen of P. gingivalis was recognized by the majority of the patients suggesting that the proteinaceous portion is an important part of the antigen, while some patients seemed to recognize the LPS or carbohydrate as the antigenic determinant.journal articl
AN ULTRASTRUCTURAL STURY OF MITOTIC CHONDROCYTES IN THE SWARM RAT CHONDROSARCOMA
Get PDFThe Swarm rat chondrosarcoma is a well established model system for the biochemical studies of cartilage proteoglycans. In this study, we observed the ultrastructure of mitotic chondrocytes in this tumor to confirm whether it is also useful as a morphological model system to examine the mitosis of chondrocytes.
As a result, the mitotic chondrocytes in this tumor contained fairly prominent cell organelles, and the endoplasmic reticulum was mainly vacuolized and the Golgi stacks were replaced by the cluster of small vesicles during the later stage of the mitotic cycle. Although the cytoplasmic division began at the telophase, the cytoplasmic cleavege furrow was so narrow that dividing chondrocytes looked as if they were partitioned by a slit. These findings are almost consistent with the changes that occurred in the mitotic chondrocytes of the tibial growth plate, although the degree of disorganization in the Golgi apparatus is slightly different. Therefore, this tumor is useful as a convenient morphological model system to examine the mitosis of chondrocytes because of the facility for taking specimens.journal articl