PURPOSE: The purpose of this study was to compare the linear sintering behavior of presintered zirconia blocks of various densities. The mechanical properties of the resulting sintered zirconia blocks were then analyzed. MATERIAL AND METHODS: Three experimental groups of dental zirconia blocks, with a different presintering density each, were designed in the present study. Kavo Everest(R) ZS blanks (Kavo, Biberach, Germany) were used as a control group. The experimental group blocks were fabricated from commercial yttria-stabilized tetragonal zirconia powder (KZ-3YF (SD) Type A, KCM. Corporation, Nagoya, Japan). The biaxial flexural strengths, microhardnesses, and microstructures of the sintered blocks were then investigated. The linear sintering shrinkages of blocks were calculated and compared. RESULTS: Despite their different presintered densities, the sintered blocks of the control and experimental groups showed similar mechanical properties. However, the sintered block had different linear sintering shrinkage rate depending on the density of the presintered block. As the density of the presintered block increased, the linear sintering shrinkage decreased. In the experimental blocks, the three sectioned pieces of each block showed the different linear shrinkage depending on the area. The tops of the experimental blocks showed the lowest linear sintering shrinkage, whereas the bottoms of the experimental blocks showed the highest linear sintering shrinkage. CONCLUSION: Within the limitations of this study, the density difference of the presintered zirconia block did not affect the mechanical properties of the sintered zirconia block, but affected the linear sintering shrinkage of the zirconia block.
Cyclic N-Oxides ; Zirconium

The present experimental study was designed to address two issues. The first was to investigate whether oxidation voltage of titanium implants influenced bone tissue responses after an in vivo implantation. The second aim was to investigate secondary stability change after 1 to 3months period. Screw-shaped implants with a wide range of oxide properties were prepared by electrochemical oxidation methods, where the oxide thickness varied in the range of 3-15micrometer. The micro structure revealed pore sizes of 1-3micrometer, the crystal structures of the titanium oxide were amorphous, anatase and a mixture of anatase and rutile type. Bone tissue responses were evaluated by resonance frequency measurements that were undertaken 1 to 3months after insertion in the rabbit tibia. It was concluded that no statistical difference of RFA values was found between the groups, RFA gains after 1month and 3months were calculated.
Bone and Bones ; Oxides* ; Tibia ; Titanium

In this study, 35 rabbits were divided into 2 groups: group A included 15 rabbits, that were intoxicated with nitrogen oxide at dose 274.48 mg/m3 of the air; and group B included 20 rabbits that were intoxicated at dose 203.04 mg/m3. Results: all of rabbits in group A died from acute pulmonary edema; PaO2 strong decreased after intoxication, CtO2 decreased at 8 hours after intoxication, PaCO2 and t.CO2 in arterial blood increased. In group B, 55% of rabbits died after intoxication, and the changes of blood gas measurements were similar to those in group A. However, these measurements in survival rabbits were decreased after 24h and then increased at 48h after intoxication
Adenomatosis, Pulmonary ; Nitrogen Oxides ; Animals ; Edema

The bionic optic nerve can mimic human visual physiology and is a future treatment for visual disorders. Photosynaptic devices could respond to light stimuli and mimic normal optic nerve function. By modifying (Poly(3,4-ethylenedioxythio-phene):poly (styrenesulfonate)) active layers with all-inorganic perovskite quantum dots, with an aqueous solution as the dielectric layer in this paper, we developed a photosynaptic device based on an organic electrochemical transistor (OECT). The optical switching response time of OECT was 3.7 s. To improve the optical response of the device, a 365 nm, 300 mW·cm ^-2 UV light source was used. Basic synaptic behaviors such as postsynaptic currents (0.225 mA) at a light pulse duration of 4 s and double pulse facilitation at a light pulse duration of 1 s and pulse interval of 1 s were simulated. By changing the way light stimulates, for example, by adjusting the intensity of the light pulses from 180 to 540 mW·cm ^-2, the duration from 1 to 20 s, and the number of light pulses from 1 to 20, the postsynaptic currents were increased by 0.350 mA, 0.420 mA, and 0.466 mA, respectively. As such, we realized the effective shift from short-term synaptic plasticity (100 s recovery of initial value) to long-term synaptic plasticity (84.3% of 250 s decay maximum). This optical synapse has a high potential for simulating the human optic nerve.
Humans ; Quantum Dots ; Bionics ; Oxides ; Optic Nerve

In order to provide bases for the control of air pollutants in Korea, the author figured out the trend on the annual increase of air pollutants emitted in the process of combustions, and estimated the amounts of air pollutants of the future years from 1975 to 1981. 1) In 1973 the consumption rate of coal was 1.2 times of that of fuel oil. The consumption rate of them would be same in 1975 and 1977. However, the rate of fuel oil would exceed that of coal in 1979. In contrast with the rate in 1979. The one of coal would be increased faster and faster to show reverse trend of consumption in 1981. 2) The estimated amounts of air pollutants emissions in the years of 1973, 1975, 1977, 1979 and 1981 were 1,561,800, 1,921,700, 2,253,300, 20769,000, and 3,145,700 tons respectively. These indicated that the amount of air pollutants in 1981 would be about 2 times of that in 1973. 3) The amounts of sulfur oxides emissions in 1981 would be 2.3 times of that in 1973, nitrogen oxides 2.2 times, carbon monoxide 1.7 times, particulate 2.0 times and hydrocarbon 2.0 times. 4) The estimated amounts of air pollutants emissions per unit area(km) in the years of 1965, 1971, 1975 and 1980 were 5.2, 14.5, 19.5 and 28.7 tons respectively. These indicated that the amount of air pollutants emissions per unit area would increase 5.5 times in 1980 comparing the one in 1965.
Air Pollutants ; Carbon Monoxide ; Coal ; Fuel Oils ; Korea* ; Nitrogen Oxides ; Sulfur Oxides

STATEMENT OF PROBLEM: Titanium has many advantages of high biocompatibility, physical porperties, low-weight, low price and radiolucency, but it is incompatible with conventional dental porcelain due to titanium's oxidative nature. Many previous studies have shown that they used the method of sandblast for surface treatment prior to porcelain application, the researchs are processing about the method of acid etching or surface coating. PURPOSE: The purpose of this research is to study the effect on bond strength between titanium and porcelain when using macro-surface treatment and micro-surface treatment and macro and micro surface treatment . MATERIAL AND METHOD: In this study, we evaluated the bond strength by using 3-point bending test based on ISO 9693 after classified 7 groups - group P : polished with #1200 grit SiC paper, group SS : sandblasted with 50 micrometer aluminum oxides, group LS : sandblasted with 250 micrometer alumium oxides, group HC : treated with 10 % hydrochloric acid, group NF : treated with 17% solution of fluoric acid and nitric acid, group SHC : treated with 10 % hydrochloric aicd after sandblsting with 50 micrometer alumium oxides, group SNF : treated with 17 % solution of fluoric acid and nitric acid. RESULTS: Within the confines of our research, the following results can be deduced. 1. Group SS which was sandblasted with 50 micrometer aluminum oxides showed the highest bond strength of 61.74 MPa and significant differences(P<0.05). The bond strengths with porcelain in groups treated acid etching after sandblasting decreased more preferable than the group treated with sandblasting only. It gives significant differences(P<0.05). 2. After surface treatments, the group treated with sandblasting showed irregular aspect formed many undercuts, in the SEM photographs. The group treated with hydrochloric acid had the sharp serrated surfaces, the group treated with the solution of fluoric acid and nitric acid had the smooth surfaces, the group with sandblasting and hydrochloric acid had irrigular and porous structure, the group with sandblasting and the solution of fluoric acid and nitric acid had craterlike surfaces. But all of the groups treated with acid etching was not found and undercut. CONCLUSION: In above results, average surface roughness increase, bond strength also increase, but surface topographs influences more greatly on bond strengths.
Aluminum ; Dental Porcelain ; Hydrochloric Acid ; Nitric Acid ; Oxides ; Titanium

PURPOSE: With gold electroforming system for the double crown, the secondary crown is electroformed directly onto the primary crown. An even thick layer of high precision can be acquired. It is thought that the retention of electroformed outer crown is primarily acquired by the adhesive force (surface tension) through the saliva which is interposed between precisely fitted inner and outer crown. The purpose of this study was to investigate the effect of taper and surface area of inner crown on the retentive force of electroformed outer crown according to the presence of saliva. MATERIALS AND METHODS: 32 titanium inner crowns with cervical diameter of 8 mm and cone angles of 0, 2, 4, 6 degrees, which had same surface area by regulated height, were machined on a lathe. Another 32 titanium inner crowns with cone angles of 0, 2, 4, 6 degrees, which had doubled surface area by increased cervical diameter, were fabricated. Eight specimens of each group, for a total of 64 titanium inner crowns, were prepared. The electroformed outer crowns were fabricated directly on the inner crowns by using electroforming machine(GAMMAT free, Gramm Technik, Germany). The tertiary frameworks were waxed-up on the electroformed outer crown and cast using nonprecious alloy(Rexillium(R)III, Jeneric(R)/ Pentronh(R) Inc., USA). The cast metal frameworks were sandblasted with alubimium oxides and cemented using resin cement(Superbond C and B, Sun Medical Co., Japan) over the electroformed copings of each specimen. Then, artificial saliva(Taliva(R), Halim Pharm Co., Korea) was sprayed between the inner and outer crown, and they were connected under 5 kg force. The retentive force was measured by the universal testing machine(Tinius Olsen 1000, Tinius Olsen, USA) with a cross-head speed of 66.67 mm/sec. The direction of cross-head travel was exactly aligned with the path of removal of the respective specimens. This measurement procedures for retentive force of electroformed outer crown with artificial saliva were repeated in the same way without presence of artificial saliva. RESULTS AND CONCLUSION: The following conclusions were drawn: 1. The retentive force of electroformed outer crown was decreased according to increased taper of inner crown(P<.05). 2. The retentive force of electroformed outer crown showed no significant differences according to surface area and the presence of artificial saliva(P>.05).
Adhesives ; Crowns* ; Oxides ; Saliva ; Saliva, Artificial ; Solar System ; Titanium

Adult ; Humans ; Male ; Nitrogen Oxides ; poisoning ; Occupational Exposure

Humans ; Nitrogen Oxides ; poisoning ; Pulmonary Edema ; chemically induced

OBJECTIVETo evaluate the accuracy of marginal and internal fit of the zirconium copings manufactured by two different computer-aided design(CAD)/computer-aided manufacturing(CAM)system on the implant abutment.

METHODSUsing different scanning mode,five Procera(®) zirconium copings and five Lava zirconium copings were fabricated on the same implant abutment, and then compared with five precious metal copings fabricated by traditional method. Fifteen abutment replica were made with die-stone and the copings were randomly cemented on them, then they were sectioned and invested. The marginal, shoulder, occlusal, and axial fit of each sample was measured by scanning electron microscopy (SEM).

RESULTSThere was no significant difference in marginal and axial fit among the three groups(P>0.05). Significant difference in occlusal fit was found among the three groups(P<0.05): Lava group showed better fit than the others(P<0.05)and Procera(®) group showed better fit than the control(P<0.05).

CONCLUSIONSThese two types of zirconium coping have clinically acceptable marginal and internal fit. The internal fit of zirconium coping may be affected by different manufacturing techniques.