• Restorative Dentistry and Endodontics
• /
• v.30 no.2
• /
• pp.128-137
• /
• 2005

In this study we measured the amount of light energy that was projected through the tooth material and analyzed the degree of polymerization by measuring the surface hardness of composites. For polymerization, Optilux 501 (Demetron, USA) with two types of light guide was used: a 12 mm diameter light guide with 840 nW/$cm^2$ light intensity and a 7 mm diameter turbo light guide with 1100 nW/$cm^2$. Specimens were divided into three groups according to thickness of penetrating tooth (1 mm, 2 mm, 0 mm). Each group was further divided into four subgroups according to type of light guide and curing time (20 seconds, 40 seconds). Vickers' hardness was measured by using a microhardness tester. In 0 mm and 1 mm penetrating tooth group, which were polymerized by a turbo light guide for 40 seconds, showed the highest hardness values. The specimens from 2 mm penetrating tooth group, which were polymerized for 20 seconds, demonstrated the lowest hardness regardless of the types of light guides (p < 0.05). The results of this study suggest that, when projecting tooth material over a specified thickness, the increase of polymerization will be limited even if light intensity or curing time is increased.

• Restorative Dentistry and Endodontics
• /
• v.31 no.6
• /
• pp.452-459
• /
• 2006

Competition will usually develop between the opposing walls as the restorative resin shrinks during polymerization. Magnitude of this phenomenon may be depended upon cavity configuration and volume. The purpose of this sturdy was to evaluate the effect of cavity configuration and volume on microleakage of composite resin restoration that has margins on the enamel site only. The labial enamel of forty bovine teeth was ground using a model trimmer to expose a flat enamel surface. Four groups with cylindrical cavities were defined, according to volume and configuration factor(Depth x Diameter / C-factor) - Group I : 1.5 mm ${\times}$ 2.0 mm / 4.0, Group II : 1.5 mm ${\times}$ 6.0 mm / 2.0, Group III : 2.Omm ${\times}$ 1.72 mm / 5.62, Group IV : 2.0 mm ${\times}$ 5.23 mm / 2.54. After treating with fifth-generation one-bottle adhesive - BC Plus$^{TM}$ (Vericom, AnYang, Korea), cavities were bulk flted with microhybrid composite resin - Denfill$^{TM}$ (Vericom). Teeth were stored in distilled water for one day at room temperature and were finished and polished with Sof-Lex system. Specimens were thermocycled 500 times between 5$^{\circ}$C and 55$^{\circ}$C for 30 second at each temperature. Teeth were isolated with two layers of nail varnish except the restoration surface and 1 mm surrounding margins. Electrical conductivity (${\mu}$A) was recorded in distilled water by electrochemical method. Microleakage scores were compared and analyzed using two-way ANOVA at 95% level. The results were as follows: 1. Small cavity volume showed lower microleakage score than large one, however, there was no statistically significant difference. 2. There was no relationship between cavity configuration and microleakage. Factors of cavity configuration and volume did not affect on microleakage of resin restorations with enamel margins only.

• Restorative Dentistry and Endodontics
• /
• v.30 no.2
• /
• pp.112-120
• /
• 2005

This study was done to evaluate whether there were any differences in microleakage of class V composite restorations according to restoration site and cavity size. Total sixty-four restorations were made in molar teeth using Esthet-X. Small ($2\;{\times}\;2\;{\times}\;1.5\;mm$) and large ($4{\times}2{\times}1.5\;mm$) restorations were made at the buccal/lingual surface and the proximal surface each. After 1,000 times of thermocycling ($5^{\circ}\;-\;55^{\circ}C$), resin replica was made and the percentage of marginal gap to the whole periphery of the restoration was estimated from SEM evaluation. Thermocycled tooth was dye penetrated with $50\%$ silver nitrate solution. After imbedding in an auto-curing resin, it was serially ground with a thickness of 0.25 mm. Volumetric microleakage was estimated after reconstructing three dimensionally. Two-way ANOVA and independent T-test for dye volume, Mann-Whitney U test for the percentage of marginal gap, Spearman's rho test for the relationship between two techniques were used, The results were as follows : 1. The site and size of the restoration affected on the microleakage of restoration. Namely, much more leakage was seen in the proximal and the large restorations rather than the buccal/lingual and the small restorations. 2. Close relationship was found between two techniques (Correlation coefficient = 0.614/ P = 0.000). Within the limits of this study, it was noted that proximal and the large restorations leaked more than buccal/lingual and the small restorations. Therefore, it should be strictly recommended large exposure of margins should be avoided by reducing unnecessary tooth reduction.

• Restorative Dentistry and Endodontics
• /
• v.24 no.4
• /
• pp.570-577
• /
• 1999

Intuitively, higher bond strengths should result in less leakage. However, the relationship between bond strengths and microleakage value is complex and not clearly understood. The purpose of this study was to evaluate the relationship between tensile bond strengths and microleakage values in the same restorations to understand the behavior of resin bonding to tooth structure. One-hundred and twenty enamel or dentin specimens from freshly extracted bovine mandibular incisors were used. The specimen was treated with 32% phosphoric acid for 15 seconds and rinsed for 20 seconds. the teeth were divided into four groups by means of wet bonding technique or dry bonding. One-Step$^{TM}$ adhesive were applied to the specimen. The specimens were immersed in 2% methylene blue solution for 7 days, and tensile bond strength and microleakage were measured. The results were as follows: 1. Significant negative correlation was found between bond strengths and micro leakage values. Hence, higher bond strengths seem to be associated with lower microleakage, and vice versa (r=-0 50, p<0.05). 2. The Enamel/Wet group showed significantly higher bond strength than Enamel/Dry one, and Dentin/Wet group showed higher strength than Dentin/Dry one (p<0.05). 3. Microleakage was significantly less ill wet bonding than in dry one at dentin (p<0.05), however, there was no significant difference between wet and dry bonding at enamel (p>0.05).

• Journal of the Korean Society of Food Science and Nutrition
• /
• v.43 no.12
• /
• pp.1929-1936
• /
• 2014

This study investigated purchasing behaviors of processed foods in high school students (male 94 and female 85) in the Yongin region. Frequency of eating processed foods was generally once (36.9%) or twice (32.4%) a day. Frequency according to processed food items was in the following order: confectionary (31.3%)> beverages (17.3%)> breads (12.3%)> instant noodles (11.7%) and milk or dairy products (11.7%)> frozen desserts (10.6%). The places for purchasing were a big mart (30.7%), convenience store (28.5%), and school cafeteria (26.8%). The reasons for purchasing were 'tasty' at 43.6% and 'hungry' at 35.2%. Main factors affecting purchasing were 'taste' at 70.9%, followed by price (16.2%)> quantity (5.6%)> nutrition (4.5%). The most important parts of food and nutrition labels were 'shelf-life' (67.0%) and 'calories' (57.5%). Degrees of confirmation of food and nutrition labeling were 'always' (12.3%), 'rarely' (28.5%), and 'sometimes' (59.2%). The reasons for not reading labels were 'unconcerned' (27.9%), 'too tiny lettering' (28.5%), 'hard to understand' (16.2%), and 'habitually' (15.1%). These results reflect low attention of high school students towards healthy food choices using food and nutrition labeling during purchasing. In conclusion, a specific education program for providing accurate product information as well as leading healthy purchasing behaviors should be required.

• Journal of the korean academy of Pediatric Dentistry
• /
• v.27 no.3
• /
• pp.419-430
• /
• 2000

The purpose of this study was to compare the microleakage pattern of preventive resin restoration using conventional composite resin and flowable composite resin that recently developed. 60 sound premolar teeth were allocated to three groups. Flowable composite resin was used for the experimental groups(Group I and II) and conventional resin for the control group(Group III). After composite filling and sealant application, all teeth were thermocycled and evaluated for microleakage under light microscope. Additionally, a variety of voids formed inside restorations were also evaluated. Data were analyzed statistically using Kruskal-Wallis test and/or Mann-Whitney U-test. The results of the present study were as follows. 1. Microleakage found in all samples was only limited to the interface of restoration margin and enamel. 2. The flowable composite resin groups (Group I, II) generally showed less microleakage than control groups (conventional preventive resin restoration) (p<0.05) 3. Various types of voids were observed in most specimens. Especially, there was a tendency for more and larger voids to be found in group I, II than group III (p<0.05).

• Journal of the korean academy of Pediatric Dentistry
• /
• v.33 no.2
• /
• pp.262-268
• /
• 2006

The purpose of this in vitro study was to evaluate the remineralizing effects of Nd : YAG laser irradiation and fluorides application on primary tooth enamel eroded by acidic drink. The materials were 30 sound primary teeth with intact smooth enamel surfaces. They were demineralized with Coca-cola at $37^{\circ}C$ for 12 hours and then irradiated by Nd: YAG laser with 6W power, $50mJ/cm^2$ energy density. and 20Hz pulse repetition. After laser irradiation, teeth were treated by three kinds of fluorides : (1) 0.05% NaF solution, (2) 1.23% APF gel and (3) 0.1% fluoride varnish. Diagnodent scores and microhardness (VHN) were measured before and after the each treatment. The results were as follows: 1. Diagnodent scores decreased to 23.51% from the initial after demineralization, and then increased to 37.37% after laser irradiation, and to 51.34% after fluoride treatment. There were significant differences between the total scores of initial, demineralization, laser irradiation and fluoride treatment (P<0.05). There was no significant difference between scores after fluoride treatment according to fluoride types. 2. Microhardness(VHN) decreased to 33.58% from the initial after demineralization and then increased to 43.99% after laser irradiation, and to 51.38% after fluoride treatment. There were significant differences between the total scores of initial, demineralization, laser irradiation and fluoride treatment (P<0.05). There was no significant difference between scores after fluoride treatment according to fluoride types.

• Journal of Korean Society of Forest Science
• /
• v.1 no.1
• /
• pp.22-29
• /
• 1962

(1) The objects of this study are to observe the possibility of regenerating a young merchantable pitch pine stand by sprouts and to compare the growth trend of sprouts with that of seedlings of same age grown under the almost same circumstances. (2) A plot of 20 year old pitch pine plantation, i.e. 200 trees on 0.1 ha of average D.B.H. 14 cm was clearcut at 20 cm above ground in April, 1945. By the late spring of that year sixty per cent of the cut stumps had sprouted. (3) Fourty to eighty sprouts were found on each stump (maximum:412 sprouts) at the first, but many of them had gradually died out leaving only four to five sprouts per stump by the time of three years after cutting. At that time only one vigorous sprout was left per stump by eliminating the weaker ones. (4) The sprouts, as they grew, started to cover the old stumps with new tissues developed from lower part of sprouts;consequently forming new root systems from the base of new tissues, and they appeared to be seedlings. When the age of sprouts was thirteen years old, the old stumps were completely decayed away and the reproduced stand from sprouts was averaged at 9.7 cm in D.B.H. and at 5.5m in height. (5) When the age of sprouts was thirteen years old, the sprouts exceeded the seedlings in both of total present growth and mean annual increment in height, volume, D.B.H. and basal area, but the seedlings began to exceed the sprouts in current annual increment of height, volume, D.B.H. and basal area at about ten years of age. The rates of increment of the seedling in height, volume, ect. were larger than those of sprouts except when they were one to four years old. From above facts, the following may be concluded: (1) In regenerating a pitch pine stand by sprouts, the lower the stump height, the better the result. (2) If no light limit exists, regenerating a pitch pine stand by sprouts is well possible even at the age of 20 year. (3) Pitch pine reproduction started from sprouts exceeds the seedlings of same age in growth under the almost same circumstances until they get ten years of age.

• Journal of Korean Home Economics Education Association
• /
• v.19 no.2
• /
• pp.131-152
• /
• 2007

The purpose in this study was to develope the concept maps of sub-units included in 'resource management and environment' area of Home Economics(HE) as an advance organizer after analyzing the overlapped and connected contents between HE textbooks and those of other subject matters(Ethics, Social Studies, Sciences, and Physical Education) taught in the middle schools. The results of this study were as follows. First, the unit of 'resource facilitation and environment' of HE is dealt in Ethics. Specifically the overlapped content in this unit between HE and Ethics is the content of the savings of resources, recycling, and environment conservation. The unit of 'work and time of youth' is dealt in Ethics and Science. The overlapped content of this unit is that of the concept of 'work'. While Ethics focuses on the general concept of work, Science focuses on the scientific concept of work. Home Economics doesn't focus on the concept of work but on how to manage the work. In the unit of the 'adolescents and their consumption', there are many overlapped contents among three subject matters, HE, Ethics and Social Studies. Second, the 7 concept maps were developed by following the steps: (1) confirming the learning objectives presented in the 'resource management and environment' area of HE; (2) identifying the overlapped and connected contents between HE and other subject matters(Eethics, Social Studies, Sciences, and Physical Education); (3) organizing the overlapped and connected contents between HE textbooks and those of other subject matters.

• KSBB Journal
• /
• v.19 no.2
• /
• pp.93-97
• /
• 2004

We investigate the effect of enzyme pretreatment using protease, carbohydrase, and lipase on improvement of sludge treatment efficiency by measuring SCOD and TCOD. The enzyme-pretreatment increases SCOD of excess sludge. In addition, the amount of sludge reduction during digestion, in terms of SCOD and TCOD, are enhanced by enzyme-pretreatment. Among pretense, carbohydrase, and lipase, pretense showed the best enhancement of the sludge treatment efficiency. Sludge digestion followed by ozone and enzyme treatments showed more effective sludge treatment when compared with ozone treatment alone. Therefore, we expect that enzyme pretreatment can be used as a useful tool for enhancing the sludge treatment efficiency.