The Bulletin of Tokyo Medical and Dental University最新文献

The purpose of this study was to evaluate dental attrition by measuring attrition volume on all types of teeth during facial growth, tooth shedding and eruption. Dental casts and cephalograms of 7 male and 7 female Mayan Tzutujil Indian children were used. Relationships were found between increase in vertical and horizontal facial growth and increase in attrition on the deciduous canines, first and second molars, permanent incisors and first molars in both arches and in both sexes. Significant increases in attrition were found on the deciduous second molars during eruption of the permanent first molars, and on the permanent incisors and first molars during eruption of the second molars in both arches and in both sexes. The results suggest that the function of attrition is 1) to compensate for increase in vertical and horizontal dimensions during facial growth, and 2) to adjust the occlusal surfaces during tooth eruption and occlusal development. In addition, an attritional index was developed to evaluate attrition among teeth. This index could be used in the future to make comparisons among different populations. Comparisons were made among Class I, II and III molar relations by using the attritional index, showing how it can be used to gain a better understanding of the characteristic patterns of dental attrition.

The cumulative effect of ischemia on the brain was investigated in cats using a repetitive transient global ischemia model. The cats were submitted to three series of repetitive ischemia of 5.0, 7.5 and 10.0-minute durations at 1-hour intervals by intrathoracic clamping of the innominate and subclavian arteries. Pathophysiological changes during and after the ischemic episodes were evaluated by monitoring the electroencephalograms (EEG), cerebral blood flow (CBF), specific gravity and 31P-MR spectroscopy (MRS). Transient 5.0, 7.5, and 10.0-minute ischemias appeared to produce a slightly more severe energy failure on the 31P MRS measurement in the animals that had previously experienced an ischemic injury than those that had not. Additionally, repetition of ischemic episodes at 1-hour intervals led to a progressive lengthening of the duration of the spontaneous electrocortical suppression that followed each ischemic episode. However, preischemic hypoxia (5% O2 for 5 minutes) resulted in minor changes in the levels of phosphocreatine and intracellular inorganic phosphate on the MRS measurement, otherwise the EEG activity declined progressively. This shut-down response of the EEG can be concluded to serve in preserving the energy state of the brain although it is not capable of preventing the development of postischemic brain edema and neuronal death.

To 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.

In 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 electron microscope 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-800H type transmission electron microscope operated at 200 kV. 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 25 kV. 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.

In 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 at near atomic resolution and showed the configuration of the hydroxyapatite structure through the cross and longitudinal sections of the crystals. Subsequently, based on the results of the observations by the authors of the ultrastructure of the tooth and bone, using the same approach, we have been able to directly examine the images of the lattice imperfections in the human tooth and bone crystals, such as the point defect structure, line defect, and face defect, in the crystals. In this report, we describe the images of the crystal fusion obtained by using the same approach from the sections of the human enamel crystals. The materials used for this study were the noncarious enamel from the freshly extracted human erupted lower first molars. The small cubes of the material 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 H and H-9000 type transmission electron microscopes operated at 200 kV and 300 kV. Each crystal was observed at an initial magnification of 300,000 times and at a final magnification of 10,000,000 times and over. We are, therefore, able to confirm that the fusion between the adjacent crystals can occur at some time during the life history of the human enamel. We sincerely believe that the electron micrographs shown in this report are the first to show the ultrastructures of the crystal fusion in the human enamel crystals at near atomic resolution.

The 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.

Stress is created by the bite force and distributed along the tooth towards the PDL structure. It is of interest to investigate the complex tooth structure, consisting of enamel, dentine, pulp, and thin cementum layer and how it functions in stress distribution. This study was intended to analyze the role of the tooth and PDL structures in stress distribution, by using a three-dimensional finite element method. A mandibular first molar was constructed for the finite element model. The bite forces were measured by Pressensor, and these bite force values were programmed to load down upon the occlusal surface of the model. The results were expressed by stress contours and principal stress graphs. The stress was found to decrease as it distributed from the occlusal surface towards the cervical portion in the dentine and the pulp. In contrast, the stress, especially a compressive stress, increased gradually in the enamel layer in the lower half of the crown, in the same direction. It was apparent in displayed pattern of stress that the stress distributed outward towards the surrounding portion of the lower half of the crown. This resulted in a uniform magnitude of the principal stresses for all aspects of the mesial and distal roots. The stresses of both roots were generally compressive stress. When comparing the stress values of sampling points positioned between the root surfaces and the periphery of the PDL (the alveolar wall), all principal stresses for those of the PDL (periodontal ligament) were less than those of the root surfaces. These findings revealed that the PDL, the dentine, and the pulp functioned in cooperation in stress reduction; and the sequences of enamel, dentine, and pulp influenced the pattern of stress distribution. The different material properties of the tooth structure in sequence was considered a very important factor for stress reduction and for the pattern of stress distribution, especially in the root.

The 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 degrees 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 Ni-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.

In a series of studies to investigate the structural features of the biological crystal, such as the tooth and bone, using an electron microscope, we examined the ultrastructure of the human 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 enamel, dentin, and bone crystals. Subsequently, based on the results of our observations of the ultrastructure of the tooth and bone crystals, we attempted to clarify the essential structural features and characteristics of the lattice imperfections in the hydroxyapatite structure composing of the human enamel, dentin, and bone crystals from the morphological viewpoint. Therefore, using the same approach, we examined the images of the lattice imperfection of the normal human enamel, dentin, and bone crystals. In this report, following the previous observation of the lattice imperfection on the point defect structure and the dislocations appearing in the inner structure of the crystal, we describe the image of the face defect structure obtained by using the same approach from the sections of the human enamel, dentin, and bone crystals, such as the stacking fault, grain boundary, and others. The materials used for this study were the human enamel, dentin, and bone crystals. The small cubes of the material 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 H and H-9000 type transmission electron microscopes operated at 200 kV and 300 kV respectively. Each crystal was observed at an initial magnification of 300,000 times and at a 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 the images of the lattice imperfections from the sections obtained from the hydroxyapatite crystal composing of the human enamel, dentin, and bone tissue, such as the grain boundary, stacking fault, and others, at near atomic resolution.