• Journal of Technologic Dentistry
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• v.27 no.1
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• pp.131-153
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• 2005

The purpose of this study was to identify the accidents happened in the college dental laboratory technique classes and to realize the level of safety education for the dental laboratory technique major students. The research data were collected from a self-administered survey distributed to the conveniently selected college students whose majors were dental laboratory technology in Suwon, Daejeon, Daegu, Kimcheon, and Icsan. The study participants were 422 freshmen, sophomore and junior students in the selected cities. All collected survey responses were encoded and analyzed in SPSS 12.0. The findings were as follows. 1. The students who had any accidents in their laboratory classes were 36% and the other 64% answered 'no.' 2. Most injuries which the participants had were not significant. 3. The medical treatment periods of most injury cases were less than one week; however, approximately 20% of the self-reported injury cases reported that their treatment periods were longer than one week. 4. The body parts frequently injured from accidents were hands with 84.7% and arms, eyes, face, head, and legs in order. 5. Concerning the materials involved in the laboratory classes, most accidents happened when working with wax in 59.9%, with plaster in 52.3%, with wire in 39.8%, with alcohol in 34.6%, and casting iron in 22.2% in order. 6. The accident-prone laboratory methods were polishing with 53.5%, pickling or sanding with 17.4%, and casting or burning with 5.8% in order. 7. Most students wore their laboratory gowns well; however, few students wore mask before dust-involved jobs. Furthermore, only 57.1% students answered their laboratory fans worked during the polishing job. 8. Approximately 54% participant students answered that they took laboratory safety education when necessary only from the class instructors. 9. The 76.1% students responded that they needed laboratory safety education at least 1-2 times every semester. 10. The survey participants answered that the primary factors for injury prevention in their laboratory were taking safety education, wearing safety equipments, and providing safety-focused facilities. Concludingly, comprehensive evaluation and monitoring for potential risk factors from both the human side and the environment side should be continually provided to minimize the college laboratory accidents.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.04b
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• pp.38-41
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• 2004

The oxidizer plays an important role in the metal chemical mechanical polishing(CMP) slurry. Currently, the oxidizer used in CMP slurry is nearly divided into several kinds such as $Fe(NO_3)_3$, $H_2O_2$, $KIO_3$, and $H_5IO_6$. It is generally known that oxidizer character of $H_2O_2$ is more effective than other oxidizers. In this work, we have been studied the characteristics for the $H_2O_2$ concentration of copper slurry, which can applicable in the recent semiconductor manufacturing process. Also, it plays an important role in the planarization of copper films using copper slurries during micro-electronic device fabrication. In this work, we confirmed that removal rate of Cu/TaN changed by $H_2O_2$ concentration on copper slurry. And we used $KMnO_4$ in the measurement method of $H_2O_2$. In analysis results, we confirmed that the difference of results is large. We thought that the difference was due to organic component existence. So in titration method of $H_2O_2$ concentration, we used $Na_2S_2O_3$ instead of $KMnO_4$ as solution. Consequently, using the titration method, we could calculate correct data reduced error. And $H_2O_2$ concentration has been adjusted to the target concentration of 0.1 wt%.

• Journal of Periodontal and Implant Science
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• v.48 no.5
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• pp.295-304
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• 2018

Purpose: This study was undertaken to evaluate the clinical and microbiological effects of an erythritol powder air-polishing device (EPAP) as a supplement to scaling and root planing (SRP) therapy in patients with moderate chronic periodontitis. Methods: Clinical and microbiological evaluations were performed at 21 sites treated with SRP (control) and 21 sites treated with SRP+EPAP (test). All examinations were performed before treatment, 1 month after treatment, and 3 months after treatment. Results: There were no significant clinical differences between the test group and the control group. Microbiological analysis revealed that the relative expression level of Porphyromonas gingivalis was significantly lower in the test group than in the control group at 1 month after treatment. Clinical and microbiological results showed improvements at 1 month compared to baseline; in contrast, the results at 3 months after treatment were worse than those at 1 month after treatment. Conclusions: In this study, both SRP and SRP+EPAP were clinically and microbiologically effective as non-surgical periodontal treatments. In particular, the SRP+EPAP group showed an antimicrobial effect on P. gingivalis, a keystone bacterium associated with the onset of chronic periodontitis, in a short-term period. Periodic periodontal therapy, at intervals of at least every 3 months, is important for sustaining the microbiological effects of this treatment.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.5
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• pp.550-555
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• 2007

The effective fracture toughness testing of materials intended for application in Micro Electro Mechanical Systems (MEMS) devices is required in order to improve understanding of how micro sized material used in device may be expected to perform upon the micro scale. ${\gamma}$-TiAl based materials are being considered for application in MEMS devices at elevated temperatures. Especially, in Alloy 4, both ${\alpha}_2$ and ${\gamma}$ lamellae were altered markedly in 3,000 h, $700^{\circ}C$ exposure. Parallel decomposition of coarse ${\alpha}_2$ into bunches of very fine (${\alpha}_2+{\gamma}$) lamellae. Parallel decomposition of coarse ${\alpha}_2$ into bunches of very fine (${\alpha}_2+{\gamma}$) lamellae. The materials were examined 2 types Alloy 4 on heat exposed specimen($700^{\circ}C$, 3,000 h) and no heat exposed one. Micro sized cantilever beams were prepared mechanical polishing on both side at $25{\sim}30{\mu}m$ and electro final stage polishing to observe lamellar orientation of same colony with EBSD (Electron Backscatter Diffraction Pattern). Through lamellar orientation as inter-lamellae or trans-lamellae, Cantilever beam was fabricated with Focused Ion Beam(FIB). The directional behavior of the lamellar structure was important property in single material, because of the effects of the different processing method and variations in properties according to lamellar orientation. In MEMS application, it is first necessary to have a reliable understanding of the manufacturing methods to be used to produce micro structure.

• Journal of Korean society of Dental Hygiene
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• v.17 no.5
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• pp.875-887
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• 2017

Objectives: The objective of this study is to provide basic data needed in developing an educational program designed to upgrade capacity and awareness of preventive dental treatment among oral health workers, by analyzing levels of awareness of preventive dental treatment and educational needs among dentists and dental hygienists. Methods: The collected data was analyzed with SPSS program ver. 19.0. The data was under t-test. Results: The frequency level of giving preventive dental treatment to patients among dentists and dental hygienists is below mid-point, 3 on the 5-point Likert scale. In terms of frequency level per item, scaling & polishing was ranked the highest, followed by periodontal maintenance, tooth-brushing instruction, and prescription and instruction of oral care product in descending order. On the questions asking how important preventive dental care they perceive to be, both dentists and dental hygienists perceived it to be highly important. When they were asked to rank those items by the importance of education, they considered periodontal maintenance as the most important one, followed by individual education of oral health, incremental oral health care, scaling& polishing, toothbrushing instruction, and prescription and instruction of oral care product. Respondents pointed out problems in running a preventive dental treatment program as follows: overwork, lack of dedicated workforce, un-fixed costs, and lack of necessary equipment. When they were asked to point out items needed to run such a program, the largest number of respondents indicated dedicated workforce placement, followed by improving awareness of the customer, and improving awareness of the dental workers. Conclusions: In order to effectively run a preventive dental treatment program, it is necessary for oral health workers to clearly understand the concept of it. It is also necessary to develop and operate an education program on preventive dental treatment targeting oral health professionals.

• The Journal of Advanced Prosthodontics
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• v.11 no.3
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• pp.162-168
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• 2019

PURPOSE. The aim of this study was to evaluate the effect of occlusal adjustments on the surface roughness of yttria-tetragonal zirconia polycrystal (Y-TZP) and wear of opposing artificial enamel. MATERIALS AND METHODS. Twenty-five Y-TZP slabs from each brand (Lava, 3M and Bruxzir, Glidewell Laboratories) with different surface conditions (Control polished - CPZ; Polished/ground - GRZ; Polished/ground/repolished - RPZ; Glazed - GZ; Porcelain-veneered - PVZ; n=5) were abraded (500,000 cycles, 80 N) against artificial enamel (6 mm diameter steatite). Y-TZP roughness (in ${\mu}m$) before and after chewing simulation (CS) and antagonist steatite volume loss (in $mm^3$) were evaluated using a contact surface profilometer. Y-TZP roughness was analyzed by three-way analysis of variance (ANOVA) and steatite wear by two-way ANOVA and Tukey Honest Difference (HSD) (P=.05). RESULTS. There was no effect of Y-TZP brand on surface roughness (P=.216) and steatite loss (P=.064). A significant interaction effect (P<.001) between surface condition and CS on Y-TZP roughness was observed. GZ specimens showed higher roughness after CS (before CS - $3.7{\pm}1.8{\mu}m$; after CS - $13.54{\pm}3.11{\mu}m$), with partial removal of the glaze layer. Indenters abraded against CPZ ($0.09{\pm}0.03mm^3$) were worn more than those abraded against PVZ ($0.02{\pm}0.01mm^3$) and GZ ($0.02{\pm}0.01mm^3$). Higher wear caused by direct abrasion against zirconia was confirmed by SEM. CONCLUSION. Polishing with an intraoral polishing system did not reduce the roughness of zirconia. Wear of the opposing artificial enamel was affected by the material on the surface rather than the finishing technique applied, indicating that polished zirconia is more deleterious to artificial enamel than are glazed and porcelain-veneered restorations.

• Tribology and Lubricants
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• v.39 no.2
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• pp.72-75
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• 2023

Silicon carbide (SiC) is used as a substrate material for power semiconductors; however, SiC chemical mechanical polishing (CMP) requires considerable time owing to its chemical stability and high hardness. Therefore, researchers are attempting to increase the material removal rate (MRR) of SiC CMP using various methods. Mixed-abrasive CMP (MAS CMP) is one method of increasing the material removal efficiency of CMP by mixing two or more particles. The aim of this research is to study the mathematical modeling of the MRR of MAS CMP of SiC with SiO₂ and TiO₂ particles. With a total particle concentration of 32 wt, using 80-nm SiO₂ particles and 25-nm TiO₂ particles maximizes the MRR at 8 wt of the TiO₂ particle concentration. In the case of 5 nm TiO₂ particles, the MRR tends to increase with an increase in TiO₂ concentration. In the case of particle size 10-25 nm TiO₂, as the particle concentration increases, the MRR increases to a certain level and then decreases again. TiO₂ particles of 25 nm or more continuously decreased MRR as the particle concentration increased. In the model proposed in this study, the MRR of MAS CMP of SiC increases linearly with changes in pressure and relative speed, which shows the same result as the Preston's equation. These results can contribute to the future design of MAS; however, the model needs to be verified and improved in future experiments.

• The korean journal of orthodontics
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• v.53 no.3
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• pp.139-149
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• 2023

Objective: To assess the color stability and translucency of full cubic stabilized zirconia (FSZ) following orthodontic bonding with different surface treatments and coffee thermocycling (CTC). Methods: This in vitro study was conducted on 120 disc-shaped specimens of FSZ. Thirty specimens were selected as the control group and remained intact. The remaining specimens were randomly divided into three groups based on the type of surface treatment (n = 30): airborne particle abrasion (APA), silica-coating (CoJet), and carbon dioxide (CO₂) laser. After metal bracket bonding in the test groups, debonding and polishing were performed. Subsequently, all specimens underwent CTC (10,000 cycles). Color parameters, color difference (ΔE₀₀), and translucency parameter (TP) were measured three times at baseline (t0), after debonding and polishing (t1), and after CTC (t2). Data were statistically analyzed (α = 0.05). Results: Significant difference existed among the groups regarding ΔE₀₀t0t2 (p < 0.001). The APA group showed minimum (ΔE₀₀ = 1.15 ± 0.53) and the control group showed maximum (ΔE₀₀ = 0.19 ± 0.02) color stability, with no significant difference between the laser and CoJet groups (p = 0.511). The four groups were significantly different regarding ΔTPt0t2 (p < 0.001). Maximal increases in TP were noted in the CoJet (1.00 ± 0.18) and APA (1.04 ± 0.38) groups while minimal increase was recorded in the control group (0.1 ± 0.02). Conclusions: Orthodontic treatment makes zirconia restorations susceptible to discoloration and increased translucency. Nonetheless, the recorded ΔE₀₀ and ΔTP did not exceed the acceptability threshold.

• Journal of the korean academy of Pediatric Dentistry
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• v.50 no.1
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• pp.65-74
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• 2023

This study compared the surface roughness and microbial adhesion characteristics of Omnichroma, a novel composite resin developed using "smart chromatic technology", with those of two other conventional composite resins with different filler compositions. A total of 144 specimens were fabricated using 3 types of composite resins: Omnichroma (nano-spherical), Filtek Z350XT (nanofill), and Tetric N-Ceram (nanohybrid) and, divided into 3 groups of 48. Finishing was performed using tungsten carbide burs. Specimens were then divided into 3 subgroups using different polishing methods: Control, SofLex, and PoGo. Surface roughness was analyzed quantitatively and qualitatively using an atomic force microscope and a scanning electron microscope. Microbial adhesion was assessed by culturing Streptococcus mutans on the specimens for 24 hours and then measuring colony-forming units attached to the upper surface. The surface roughness (Ra) of Omnichroma was 0.123 ㎛ after finishing, and it exhibited a smooth surface compared to the other resins. However, after polishing, there were no significant differences in the surface roughness between the three composite groups, regardless of the polishing methods. The surfaces of the Control subgroups were significantly rougher than those of the SofLex subgroups in all 3 composite groups. However, except for Tetric N-Ceram, there were no significant differences between the Control and PoGo subgroups in the other composite groups. Microbial adhesion assessment showed no significant differences between any of the 3 composite resin subgroups; however, Omnichroma exhibited higher microbial adhesion than the other two composites. No significant correlation was observed between surface roughness and microbial adhesion.

• The Journal of the Korean dental association
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• v.49 no.1
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• pp.22-32
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• 2011

This paper reviewed the following subheadings and a few selected references in each section were discussed: ${\cdot}$ Sealant placed over caries; is it possible? Initial caries which is not sticky during proving is possible to be placed with sealants. ${\cdot}$ Prophylaxis of fissure; which method is most effective? Mechanical preparation with fissurotomy or resin polishing bur is one of the most effective method to clean the pit and fissure. ${\cdot}$ Glassionomer cement as a sealant; GIC, wheather it released fluoride or not, cannot be as cost-effective as resin-based sealants. ${\cdot}$ Sealant products; Color(white vs opaque), fluoride(containing vs not), filler component(filled vs non-filled) do not influenced the quality and retention of sealants. ${\cdot}$ Use of intermediate bonding agent to improve retention; Intermediate bonding may increase the retention rate of sealants ${\cdot}$ Penetration method of sealants; Several methods including waiting before light curing are recommended.