Shika gakuho. Dental science reports最新文献

In this study, the authors have attempted to discover optimum conditions for eliminating all porosity, except what is caused by manual error, in the surfaces of Die Stone. Five vinyl-porisiloxane impression materials, two other kinds rubber impression materials, and two kinds of die materials were used. Die materials were poured at intervals of 0, 15, 30, 60, and 120 minutes after the impression had been removed. Cast-surface porosity was measured by means of SPICCA II. Results 1. Practically surface porosities were not scarcely observed in casts made from any of the impression materials except vinyl silicone rubber. Among the five vinyl-polysiloxane impression materials, Hydrophilic Exaflex produced the least porosity. 2. Porosity in casts made with Provil tended to decrease definitely as pouring time progressed. This tendency occurred with no other materials. 3. When the die material was mixed at a low water-powder ratio, cast-surface porosity was reduced in the case of all materials except President. 4. Concentration of hydrogen gas, which was released from all vinyl-polysiloxane impression materials, decreased with the passing of time. 5. In the case of Provil, a correlation existed between hydrogen-gas concentration and the degree of cast-surface porosity. But no similar correlation was observed in the case of any other vinyl-polysiloxane impression materials.

Unlabelled: The free nerve endings and Ruffini type endings in the cat mandibular molar buccal periosteum (posterior periosteum) were selectively stimulated with specific displacements of various velocities and frequencies and the afferent impulses generated by the nerve endings were recorded.

Results: 1. There were two types of fast-adapting free nerve endings, discharging on effects and off-effects in response to square wave pressure stimuli and ramp mechanical stimuli and on-effects only. 2. Unencapsulated endings were distributed near the mentale foramen and again there were two types of fast adapting endings, discharging on effects and off effects in response to square wave pressure stimuli and ramp mechanical stimuli, and on-effects only. 3. Slow-adapting free nerve endings were also observed through response to square wave pressure stimuli and ramp shaped pressure stimuli. These were difficult to differentiate from the slow adapting Ruffini-type endings. 4. Ruffini type endings were slow adapting types, exhibiting impulse frequency displacement velocity curves of F = 39.627V0.743 (F = impulse frequency, V = displacement velocity, r = 0.999, n = 12 and p less than 0.001). The number of impulse displacement curves was proportional to the displacement, with F = 1.024S0.767 (F = impulse frequency, S = displacement, r = 0.981, n = 6 and p less than 0.001). 5. Free nerve endings followed Stevens' power function law, dropping in order from fast-adapting units (10 units) to intermediate type sensory units (21 units) and slow-adapting sensory units (20 units), with 0.894 +/- 0.103, 0.684 +/- 0.022 and 0.650 +/- 0.023, respectively. Values for slow adapting Ruffini type endings followed the previous order. 6. Slow adapting free nerve endings responded to triangular vibration stimuli at 0.1 Hz to 240 Hz and the lower frequency limit of 0.1 Hz (actually it was below 0.1 Hz but this value was adopted in order to facilitate the recording of the difference to fast adapting free nerve endings) was considerably lower than the 0.6 Hz to 1 Hz range for fast-adapting free nerve endings. The structure and functions of the nerve endings in the cat posterior periosteum were investigated and it was found that the relationship between the impulse frequency and displacement velocities and displacement amplitude for slow-adapting Ruffini-type endings followed Stevens' power factor law. In conclusion, it was demonstrated that the slope constant follows the order of fast-adapting free nerve endings, intermediate type free nerve endings and slow-adapting free nerve endings.

The author biochemically evaluated the possible application of 4 types of alpha-cyanoacrylate adhesive agents (methyl, ethyl, isopropyl and isobutyl) in dentistry. A semiconductor temperature sensor was used to measure alpha-cyanoacrylate polymerization-temperature maximum heat, and an oscilloscope was employed to measure heat value. Amounts of formaldehyde eluted from the soluble component of alpha-cyanoacrylate was measured colorimetrically. In addition, to evaluate the effects of alpha-cyanoacrylate on pulp tissue, the soluble component of alpha-cyanoacrylate polymer was added to mouse macrophages. Changes in the numbers and morphology of macrophages and their glucose consumption in the supernatant medium were studied and compared with corresponding data obtained when formaldehyde alone was used. (1) During the polymerization of alpha-cyanoacrylate, when a glass fiber disc filter was used, the temperature increased by 19.1 degrees C in 1 microliter with methyl and by 8.6 degrees C with isobutyl. Even with the same alkyl, however, polymerization heat differed depending on the structure and constitution of the adhesive material and varied widely according to experimental conditions. (2) A mean maximum temperature of 1.7 degrees C in the dentin floor during polymerization of 10 microliters of alpha-cyanoacrylate monomer with methyl suggests no thermal injury to the pulp. (3) Formaldehyde was detected in all 4 adhesives when alpha-cyanoacrylate was dropped into distilled water for polymerization. Since, with each alkyl, the amount of eluted formaldehyde reached a maximum after 1 day of immersion, continuous elution of formaldehyde by hydrolysis was negligible. (4) A greater amount of formaldehyde was eluted from the polymer with methyl and ethyl, which have less Cs, than from the polymer with isopropyl and isobutyl, which have more Cs. These findings suggest that alkyl type affects the amount of eluted formaldehyde. (5) The soluble component of the alpha-cyanoacrylate polymer, either methyl or ethyl, had no effect on the number or morphology of mouse macrophages, as compared with corresponding data obtained when sterilized distilled water was used as a control. Isopropyl and isobutyl, however, decreased cell count and inhibited the extension of the sell soma. (6) The effects of isopropyl and isobutyl on the numbers and morphology of macrophages were similar to those of formaldehyde used alone at a concentration of 8 ppm or more. These findings suggest that, under the present experimental conditions, the above-mentioned changes in macrophages are the effects of about 8 ppm of formaldehyde. (7) The rate of glucose consumption by macrophages with methyl or ethyl was as high as that with the control.(ABSTRACT TRUNCATED AT 400 WORDS)

Observing hemodynamic changes occurring during dental treatment performed under local anesthesia is very important. Although many reports on such changes have been made on the basis of blood pressure and heart rate indexes, few have been made on the basis of parasympathetic activity. This is a report of a study on observations of parasympathetic activity on the basis of the index of R-R interval variation in ECG. A multipurpose monitoring system was used to observe and record hemodynamic changes in 52 patients undergoing dental treatment under local anesthesia. In addition, parasympathetic activity was observed on the basis of the index of the coefficient of variation of the R-R interval in ECG (CVR-R = SD/MEAN x 100%). To evaluate R-R interval variations in ECG during dental treatment clearly, comparisons were made between subjects to whom atropine sulfate was administered (prior to treatment) and subjects to whom no drug was administered. In instances of which the subject experiences no unpleasant symptom (for instance, the fainting) during dental treatment, comparative examinations of R-R interval variations in ECG were made at various points during the course of therapy. In instances of which the fainting was induced, examinations of these variations were made during, before, and after the occurrence of the fainting. Results and Conclusions 1. In measuring R-R interval variations in ECG, maintaining stable heart rates and respiratory frequency and depth made it possible to evaluate parasympathetic activity during dental treatment. 2. Consistently low CVR-R values after administration of atropine sulfate clearly showed that patients treated in this way were in a state of parasympathetic blockade. 3. Patients to whom atropine sulfate was administered demonstrated higher values for systolic and diastolic blood pressure and for heart rate than controls: and their posttreatment recovery was slower. 4. Increasing age produced a correlative decrease in CVR-R during both the pretreatment rest period and immediately before treatment. 5. Systolic and diastolic blood pressure and heart rate increased at local anesthesia and maintained such levels until the end of treatment in no fainting cases, however, CVR-R increased just before the end of treatment. This finding leads to the assumption that, as a result of intensified sympathetic activity at the initial stage and the maintenance of this condition, parasympathetic activity increases just before the end of therapy to keep hemodynamic activity in balance.(ABSTRACT TRUNCATED AT 400 WORDS)

Unlabelled: It is considered that the appearance of Silent Period (SP) during food crushing may relieve tissue injury caused by sudden change of maxillo-mandibular impactive force. In connection with this phenomenon, the relation between changes in vertical velocity of mandibular movement and the appearance of SP during food crushing was investigated. In addition, efforts were made to clarify the influences of lack of periodontal pressoreceptive information on the appearance of SP. Subjects were ten males (aged 24 to 31) with natural dentition and no masticatory dysfunction. Electromyograms were recorded on 4 lead locations: the central parts of each masseter and the anterior bundles of each temporal muscle. A Mandibular Kinesiograph and electromyograph were used to record simultaneously mandibular movement and myoelectric discharge during food crushing for the sake of comparing changes in mandibular position, vertical velocity of mandibular movement and muscular activity. Eight kinds of foods of various textures were selected for use in the examinations: dry macaroni, rice cracker, raw carrot, pickled thistle root, pickled radish, raisin, synthetic rubber block and softened chewing gum. The food was positioned on the occlusal table of the lower first molar on the habitual masticatory side of each subject. Then the subject was required to close his mouth rapidly to crush the food at a single masticatory stroke. Two experimental conditions were established in order to clarify the significance of periodontal pressoreceptive information on the appearance of SP: (1) normalcy and (2) infiltration anesthesia of the periodontal tissues of the upper and lower first-molar region on the habitual masticatory side. Results 1. SP appeared during a single masticatory stroke in response to sudden decreases or increases of vertical velocity of mandibular movement. 2. The frequency of the appearance of SP depends on the crushing characteristics of the food which is tested. For softened chewing gum and the synthetic rubber block, only one SP occurred; two SPs occurred in the cases of pickled radish and raisin; three SPs in the cases of raw carrot and pickled thistle root; and more than four SPs in the cases of dry macaroni and rice cracker. 3. Lack of periodontal pressoreceptive information resulting from anesthesia had no effect on the appearance of SP.

Conclusions: 1. Sudden changes in vertical velocity of mandibular movement may depend on the crushing characteristics of the food which is crushed.(ABSTRACT TRUNCATED AT 400 WORDS)

Unlabelled: Masticatory dysfunction in patients with unilateral cleft lip and palate was studied on the basis of electromyograms of the masticatory muscles. The purpose of the study was to elucidate the origin of the dysfunction by means of comparisons among electromyograms of masticatory muscles in cases of normal occlusion, reversed occlusion and reversed occlusion caused by unilateral cleft lip and palate. Subjects were 10 cases of normal occlusion (10y2m-11y10m), 10 cases of reversed occlusion (7y2m-11y2m) and 20 cases of unilateral cleft lip and palate (8y0m-14y3m). In each subject, electromyograms of the masseter and anterior venters of the temporal muscles at the isometric-contraction phase were recorded by means of the surface-electrode method with mandible loads of 1-5 kg. The electromyograms were analyzed quantitatively by means of an electromyographic device called a Turn Counter. Relations between loads and amplitude as well as numbers of turns were examined. At the same time maximum masticatory pressure and occlusal contact points were measured and then examined in comparison with electromyographic findings.

Results: 1. Correlation coefficients between loads and amplitudes as well as numbers of turns decreased among the groups in this order: normal occlusion, reversed occlusion and cleft-caused reversed occlusion. Significant differences were observed between the normal-occlusive group and the reversed and cleft-caused reversed-occlusive groups. 2. No. difference was observed between the normal-occlusive and reversed-occlusive groups in terms of correlation coefficients between total sums of amplitudes and turns of the 4 masseter muscles (right and left masseters and anterior venters of the temporal muscles) and loads. Correlation coefficients in the cleft group were significantly smaller than those in the other 2 groups. 3. Because of great differences in regression coefficient among individuals, no synergic contraction pattern of the 4 mastication muscles (right and left masseter and temporal muscles) could be specified. 4. The A/T ratio of masseters in the cleft group was significantly smaller than those in the normal- and reversed-occlusive groups. 5. Under maximum load, the activity ratio of the 4 masseter and temporal muscles was 1:1 in the normal- and reversed-occlusive groups, whereas temporal-muscle activity predominated over masseter-muscle activity in the cleft group. 6. Maximum masticatory pressure decreased in the order: normal-occlusive, reversed-occlusive, and cleft caused occlusive. No correlation with electromyographic findings was observed.(ABSTRACT TRUNCATED AT 400 WORDS)

It has recently been suggested that fibroblasts in periodontal ligaments have cytochemical characteristics similar to those of osteoblasts and different from those of other connective tissues. The authors isolated clonal cell lines of fibroblast-like cells from human periodontal ligaments in order to clarify their nature. Digestion with collagenase and hyaluronidase was used to isolate the cells from a human periodontal ligament. The cells were then plated in a 96-hole microplate. A single cell in a conditioned medium containing 20%FBS was placed in each hole. From these single cells large colonies ware subcultured. Subculturing was done every 8 days until more than 20 successive generations had been produced. The method developed by Lowry et al. was used to determine the ALPase activity of the cultured cells. From the 768 cells cultured from human periodontal ligament, 7 clonal cell lines were isolated in vitro. Cultures of these clonal cell lines resulted in typical, spindle-shaped, fibroblast-like cells, all of which were homogeneous. Very high ALPase activity was observed in 4 of the 7 cell lines. Enzyme reaction products occurred mainly along cell membranes. These stable clonal cell lines provide suitable systems for in vitro studies related to morphological and functional analysis of fibroblasts in the periodontal ligament.

Unlabelled: To elucidate the biological characteristics of both pocket and long junctional epithelia in experimental periodontitis, elastic rubber was inserted between the first and second molars of the left maxilla in rats. The rubber was removed after a week. An immunohistochemical study using anti-laminin and permeability experiments using peroxidase were conducted; examinations were made of ultrastructures and lanthanum; and a morphometric analysis was made of the distribution of capillaries immediately below the epithelium.

Results: 1. Periodontal pockets formed from 5 days to 2 weeks after removal of the rubber. The long junctional epithelium was appearent from the fourth week after removal. Immunohistochemical study showed that laminin was located at the internal and external basal laminae in the long junctional epithelium but not on the surface of the pocket epithelium. 2. Electron microscopy showed the pocket epithelium to consist of flattened cells aligned parallel to the tooth surface in the coronal portion. The epithelium, which included numerous vacuoles, manifested especially wide intercellular spaces in which a large number of polymorphonuclear leukocytes were evident. Bacteria surrounded by neutrophils could be seen on the surface of the cementum in the pocket. Invading neutrophils split the epithelium at the central portion of the pocket. In the apical portion, the epithelium formed spindles that adhered to the cementum by means of half-desmosomes. Many neutrophils and fenestrated capillaries were observed in connective tissue immediately below the epithelium. 3. The long junctional epithelium consisted of 2 or 3 cell layers aligned parallel to the tooth surface. Intercellular spaces in the long junctional epithelium were as wide as those in the pocket epithelium and contained a small number of lymphocytes and a few neutrophils. Half-desmosomes were detected between the epithelial cells and the cementum. From the central to the apical region, epithelial tissues assumed a knife-edge form. Desmosomes and gap junctions occurred among these cells. Dense granules containing a limiting membrane and homogeneous electron-dense material were observed int he peripheral cytoplasm. Although fibroblasts aligned parallel to the epithelium occurred in them, few collagen fibers, inflammatory cells and capillaries were to be recognized in the connective tissue. 4. Permeability experiments in the pocket and the long junctional epithelium produced analogous results. Light microscopy showed that, in both epithelia, peroxidase penetrated into intercellular spaces and leaked into the pocket. Electron microscopy showed that, as an electron-dense material, lanthanum was detected in intercellular spaces and connective tissues.(ABSTRACT TRUNCATED AT 400 WORDS)

Unlabelled: This study aims to evaluate the influence of the anodic potential on metal-components dissolution from dental alloys and is intended to serve as an aid in the investigation of dental metal eruption (metal allergy). In the experiments, anodic potentials were applied electrochemically to various dental alloys in a 0.9% NaCl solution. Thereafter amounts of metal-component dissolution were measured by means of atomic absorption spectrophotometry. In addition, relations between metal-component dissolution and electrochemical characteristics (anodic polarization and charge transfer calculated from current density-time transients) were considered.

Results: 1. Breakdown potentials determined on the basis of anodic polarization profiles agreed with potentials of remarkable increase in component dissolution. 2. Current density-time transients gave good indications of alloys' corrosion tendencies. Correlations between charge transfer and total amounts of metal-component dissolution were comparatively good. 3. Metal-component dissolutions in various alloys at fixed anodic potentials 1) Cu and Zn were found to dissolve slightly from gold alloys (types II and IV) at potentials above 200 mV (vs SCE). 2) Ag, Pd, Cu, and Zn were found to dissolve from the Ag-Pd-Cu-Au alloy at potentials above 100 mV. A comparatively large amount of Zn was released at low potentials. Amounts of Ag and Cu dissolution increased rapidly at 300 mV and 500 mV respectively. Although traces of it were detectable at low potentials, dissolution of Pd increased remarkably at 500 mV. 3) Ag, In, and Zn were found to dissolve from the Ag-In-Zn alloy at potentials above O mV. Amounts of In and Zn dissolution increased above 20 mV. The increase was especially remarkable in the case of In. 4) Sn and Zn were found to dissolve from the Ag-Sn-Zn alloy at potentials above -200 mV; Ag dissolved from the same alloy at potentials above 100 mV. Amounts of Sn and Zn dissolution increased at potentials above 100 mV. This was especially true in the case of Sn. 5) Ni, Cu and Si were found to dissolve from the soft type Ni-Cr alloy (9.0 wt% Cr) at potentials above -100 mV. Cr, Mn, and Fe dissolved from the same alloy at potentials above 0 mV; and Co at potentials above 200 mV. Metal-component dissolution was greater in the case of this alloy than in those of all the other alloys used in this study. A considerable amount fo Ni was released at 0 mV.(ABSTRACT TRUNCATED AT 400 WORDS)

Unlabelled: The performance of the rotate/rotate CT scanner TCT-700 S (Toshiba) was evaluated on the basis of the item entitled "User's initial acceptance tests (phase II)" set forth in "Standard of performance evaluation for x-ray computed tomography (second recommendation)" proposed by Takenaka et al. (1982). This second report in the series describes measurements of exposure and the relation between exposure and such other performance aspects as noise and contrast resolution. The exposure-performance recommendation proposes measurements of average exposure in the scanning field and a radial exposure profile.

Results: 1. In the case of multiple scanning, average exposures in the field were uniform because all surfaces of the perpendicular object were oriented toward the incidence of the x-ray beam. At a minimum scanning speed of 1.8 second, however, a discrepancy of 3 times occurred in exposures observed reciprocally from the left and right sides of the object. This phenomenon indicates that only one-half of the object surface is oriented toward the x-ray beam and that the x-ray tube and detectors rotate in mutually opposite directions. In the case of multiple scannings, when slice thicknesses were 10 mm, 5 mm and 2 mm, average exposures were almost uniform. But with a slice thickness of 1 mm, average exposure was twice as great. This measurement indicates inadequate collimation in the case of a 1 mm slice thickness. These average exposures were roughly proportional to the mAs (product of tube current and scan speed) in the range between a minimum of 100 mAs and a maximum of 1200 mAs. 2. Noise increased in proportion to decrease of average exposure.(ABSTRACT TRUNCATED AT 250 WORDS)