• Restorative Dentistry and Endodontics
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• 제19권1호
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• pp.169-179
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• 1994

The purpose of this study was to compare and evaluate the bleaching efficacy of three nonvital bleaching techniques: Walking bleaching, Walking bleaching and heat application, and Walking bleaching and bleaching light application. 36 extracted anterior teeth with intact crowns were immersed in 5 % sodium hypochlorite solution for twenty-four hours to loosen extrinsic debris. Lingual access openings were prepared in all teeth and the pulps were extirpated. The teeth were stored in 5% sodium hypochlorite for twenty-four hours to open the dentinal tubules and they were stained via whole blood. Once the teeth were stained, they were evaluated with Colorimeter. The teeth in each group were ranked from lightest to darkest and divided equally into three experimental groups in which the following bleaching techniques were used. Intracoronal base was placed 2mm below cementoenamel junction. Group 1 Walking bleaching (Superoxol + Sodium perborate) Group 2 Heat application + Walking bleaching (Superoxol+Sodium perborate) Group 3 Light application+Walking bleaching (Superoxol+Sodium perborate) The bleaching agents were changed every 3 days and the teeth were bleached for a total of 14 days. The teeth were evaluated with Colorimeter before the start of any bleaching and on day 14. The results were as follows: 1. At the end of 14 days, all the sample teeth demonstrated the increase of Lightness Index at cervical 1/3 of crown (p<0.05) Lightness Index was significant difference in group 2 and 3, but there were some minor differences among groups (p>0.05). 2. In all groups, there was significant difference in red chromacity (p<0.05), but there were some minor differences among groups (p>0.05). 3. In all groups, there was no significant difference in yellow chromacity (p>0.05).

• Restorative Dentistry and Endodontics
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• 제25권1호
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• pp.123-132
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• 2000

To overcome problems of conventional glass ionomers, resin components have been added to glass ionomers. On a continuum between glass ionomers and composites are a variety of blends, employing different proportions of acid-base and free radical reactions to bring about cure. Popular groups defined between the ends are resin-modified glass-ionomers(RMGIs), polyacid-modified composite resins(Compomers) and ionomer modified resins. These groups show different clinical properties, and in selecting these materials for a restoration, one should sufficiently understand these different setting properties. In this study, some difference in the setting characteristics of different groups of hybrid ionomers were examined. Two RMGIs (Fuji2 LC,GC / Vitremer, 3M), three Compomers (Dyract AP, Dentsply / F2000, 3M / Elan, Kerr) were involved in this study. The identification of the setting characteristics of different groups was achieved by a two-stage study. First, thermal analysis was performed by a differential scanning calorimeter, and then the hardness of each group at different depth and time were measured by a micro-hardness tester. Thermal analysis was performed to identify the inorganic filler content and to record the heat change during setting process. The setting process was progressed for each material by chemical set mode and light-cured mode. In the hardness test, samples of materials were prepared with a 6mm-diameter metal ring, and the hardness was measured at the top, and 1mm, 2.5mm, 4mm below at just after a 40 second-cure, and after 10 minutes, 24 hours, and 7 days. Statistical analysis was performed by Mann-Whitney rank sum test to assess significant differences between set modes and types of materials, and by ANOVA and T-test to evaluate the statistical meanings of data at different times and depths of each materials. Followings are findings and conclusions derived from this study. Thermal analysis; 1. Compomers show no evidence of chemical setting while RMGIs exhibit heat output during the process of chemical setting. 2. Heat of cure of RMGIs exceed Compomers. 3. The net heat output of RMGIs through light-cured mode is higher than through chemically set mode. Hardness test; 1. Initial hardness of RMGIs immediately after light cure is relatively low, but the hardness increases as time goes by. On the contrary, Comomers do not show evident increase of the hardness following time. 2. Compomers show a marked decrease of setting degree as the depth of the material increases. In RMGIs, the setting degree at different depths does not significantly differ.

• 대한기계학회논문집B
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• 제28권11호
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• pp.1302-1314
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• 2004

Turbulent heat transfer to $CO_2$ at supercritical pressure flowing in vertical tubes is investigated using direct numerical simulation (DNS). A conservative space-time discretization scheme for variable-density flows at low Mach numbers is adopted in the present study to treat steep variations of fluid properties at supercritical pressure just above the thermodynamic critical point. The fluid properties at these conditions are obtained using PROPATH and used in the form of tables in the simulations. The buoyancy influence induced by strong variation of density across the pseudo-critical temperature proved to play a major role in turbulent heat transfer at supercritical state. Depending on the degree of buoyancy influence, turbulent heat transfer may be enhanced or significantly deteriorated, resulting in local hot spots along the heated surface. Based on the results of the present DNS combined with theoretical considerations, the physical mechanism of this local heat transfer deterioration is elucidated.

• Restorative Dentistry and Endodontics
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• 제25권2호
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• pp.219-224
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• 2000

The purpose of this study is for evaluating the effect of MS Coat desensitizing agent in clinical situation. In this study total 60 teeth of 30 patients who is feeling hypersensitivity after periodontal surgery were treated with MS Coat desensitizing agent, and 20 teeth with saline solution for placebo effects and evaluated. All teeth were cleaned with rubber cup and pumice, after then the antibacterial agent was applied for 20 seconds and simply isolated using cotton roll Desensitizing agent was applied with a specific instrument in the manufacturers package by abrading motion for 10 seconds and re-done 8 times. Tactile stimulus with sharp explorer, air stimulus with syringe of dental unit, $7^{\circ}C$ cold water stimulus using micropipette applicator was done to evaluate hypersensitivity before apply test agent, immediate after application, 1 week after, and 3 month after application. The degree of hypersensitivity was recorded using 100mm Visual Analogue Scale and compared between group and evaluation times. From this clinical study sensitivity to the stimulus was significantly induced in both groups and MS Coat made a significant reduction in VAS score than placebo group did(p<.01). The results of this study could demonstrate that MS Coat desensitizing agent can use effectively to heat dentinal hypersensitivity.

• 대한기계학회논문집B
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• 제25권5호
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• pp.619-626
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• 2001

The present experimental and numerical study investigate flow and natural convection heat transfer characteristics of a composed rectangular-parallelogrammic enclosure with a guide vane. The governing equations for the two-dimensional, laminar, natural convection process in an enclosure are discretized by the control volume approach which insures the conservative characteristics to be satisfied in the calculation domain, and solved by a modified SIMPLE algorithm. The momentum and energy equations are coupled through the buoyancy term. In this results of experimental study, the natural convection heat transfer characteristics was well coincided with conclusions of other earlier experimental researches and numerical analysis.

• Restorative Dentistry and Endodontics
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• 제16권1호
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• pp.1-5
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• 1991

The purpose of this study was to investigate the color stability of 2 light - polymerized veneer resins and 3 heat - polymerized veneer resins. Five specimen discs of each brand were immersed in distilled water at $37^{\circ}C$, in darkroom for 120 days. The distilled water was changed on every third day to prevent contamination from micro - organisms. The color characteristics of all the samples were measured by computer controlled spectrophotometer. The appearence was characterized by means of the $L^*$, $a^*$ and $b^*$ uniform color space(CIELAB) and total color difference was calculated. The following results were obtained 1) ${\Delta}E^*ab$ - value in all brand except IS is were greater than 1 perceptable in visual evaluation. 2) ${\Delta}E^*ab$ - value in VI, IS and VG were lower than upper limit of acceptablilty(3.3 in ${\Delta}E^*ab$). DC was the worst in color stability and was changed into yellow color.

• Nuclear Engineering and Technology
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• 제47권4호
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• pp.434-442
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• 2015

The advanced passive pressurized water reactor (PWR) is being constructed in China and the passive residual heat removal (PRHR) system was designed to remove the decay heat. During accident scenarios with increase of heat removal from the primary coolant system, the actuation of the PRHR will enhance the cooldown of the primary coolant system. There is a risk of power excursion during the cooldown of the primary coolant system. Therefore, it is necessary to analyze the thermal hydraulic behavior of the reactor coolant system (RCS) at this condition. The advanced passive PWR model, including major components in the RCS, is built by SCDAP/RELAP5 code. The thermal hydraulic behavior of the core is studied for two typical accident sequences with PRHR actuation to investigate the core cooling capability with conservative assumptions, a main steam line break (MSLB) event and inadvertent opening of a steam generator (SG) safety valve event. The results show that the core is ultimately shut down by the boric acid solution delivered by Core Makeup Tank (CMT) injections. The effects of CMT boric acid concentration and the activation delay time on accident consequences are analyzed for MSLB, which shows that there is no consequential damage to the fuel or reactor coolant system in the selected conditions.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1998년도 추계 학술대회논문집
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• pp.78-83
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• 1998

A finite-difference method based on conservative supra characteristic method(CSCM) type upwind flux difference splitting has been studied on the bluntness effect on the wall heat transfer rate and wall pressure over blunt-body. The results show that the stagnation heating varies inversely with the square root of the nose radius.

• Restorative Dentistry and Endodontics
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• 제30권4호
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• pp.335-343
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• 2005

세균의 용혈활성은 세균이 숙주 내에서 생존하기 위해 필요한 철을 획득하기 위한 특성이며 기능 면에서 볼 때 숙주에 대한 중요한 독력인자로 간주될 수 있다. 본 연구에서는 괴사치수 및 치근단 치주염으로 진단된 환자의 근관에서 분리한 Prevotella nigrescens의 용혈활성을 다양한 조건 하에서 측정하여 그 특성을 규명하는 것을 목적으로 한다. 1. 임상에서 분리한 P. nigrescens와 표준균주인 P. nigrescens ATCC 33563에서 모두 용혈활성이 나타났다. 2. 사람, 면양 및 말 세 가지 종에 대해 용혈활성을 비교한 결과 사람의 적혈구에서 가장 강한 용혈활성을 나타내었다. 3. 용혈소 억제제인 $NaN_3$와 dithiothreitol(DTT)는 농도의존적으로 P. nigrescens의 용혈활성을 감소시켰다 (p<0.05) 4. P. nigrescens가 최대 용혈활성을 나타내는 최적의 pH는 4이었으며, $50^{\circ}C$이하의 온도에서는 용혈활성을 보였으나 $95^{\circ}C$에서 급격히 감소하였다. 5.배양조건에 따른 P. nigrescens의 용혈활성을 비교한 결과 $10\%\;CO_2$배양기에 배양한 경우 혐기성 조건에서 배양한 것보다 더 높은 용혈활성을 보였다.

• Restorative Dentistry and Endodontics
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• 제46권1호
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• pp.6.1-6.10
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• 2021

Objectives: The aim of this study was to evaluate the corrosion resistance of heat-treated (Reciproc and WaveOne) and non-heat-treated (ProTaper and Mtwo) superelastic nickel-titanium endodontic files when immersed in a 5.25% sodium hypochlorite solution. Materials and Methods: Anodic polarization curves were obtained with potential sweeps that began at the open circuit potential or corrosion potential (E_corr). The pitting potential (E_pit) was identified on the anodic polarization curve as the potential at which a sudden increase in current was observed. The micromorphology of the 28 tested files was analyzed before and after the electrochemical assay using scanning electron microscope (SEM). The data were analyzed using 1-way analysis of variance with the post hoc Bonferroni test (for E_corr) and the Student t-test for independent samples (for E_pit). Results: The mean E_corr values were 0.506 V for ProTaper, 0.348 V for Mtwo, 0.542 V for Reciproc, and 0.321 V for WaveOne files. Only WaveOne and Protaper files exhibited pitting corrosion, with E_pit values of 0.879 V and 0.904 V, respectively. On the SEM images of the ProTaper and WaveOne files, cavities suggestive of pitting corrosion were detected. Conclusions: Signs of corrosion were observed in both heat-treated and non-heat-treated files. Of the evaluated files, WaveOne (a heat-treated file) and ProTaper (a non-heat-treated file) exhibited the lowest corrosion resistance.