Earticle

Purpose:This study examined the effect of wettability of gypsum materials and rubber impression material on the marginal fitness of zirconia copings. Methods: Three commercially available gypsum materials(Fugirock EP, Snow Rock, Tuff Rock) and three zirconia blocks(iJAM Emerald, LUXEN Smile block, ICE Zirkon transluzent) were studied. The zirconia copings were fabricated by using dental CAD/CAM system. Contact angles on the impression materials were measured with contact angle measuring device. Silicone replica method was used to measure the marginal fitness and cutting was performed on the bucco-lingual and mesio-distal sides. It were observed with a stereomicroscope at °ø40 magnification. The data were statistically analyzed with One-way ANOVA. Results: Mean values of contact angles were 58.3±0.7。for Tuff Rock, 77.5±0.5。for Fugirock EP and 87.8± 0.5。for Snow Rock and the difference between them was statistically significant(p<0.05). The smallest values of marginal fitness for the JF groups were 30.7±3.0㎛ for bucco-lingual direction, 29.3±3.0㎛ for mesio-distal direction. One-way ANOVA showed statistically significant difference between groups for marginal fitness(p<0.05). Conclusion: Tuff rock gypsum material had superior wettability to others. The mean marginal fitness of the Tuff rock gypsum material group were significantly better than other groups. Thus they can be also expected to show clinically satisfactory marginal fitness.

Purpose: The purpose of this study is to measure and compare a degree of setting expansion of dental stone by time depending on the mixing methods and mixing ratios of dental stone, to compare the surface state of each specimen with the use of an optical camera with microscope, and thereby to provide a fundamental material for making dental prostheses. Methods: The test on setting expansion of dental stone is based on ISO 6873. With two different mixing ratios and three kinds of stone mixing methods, test groups were created, and a total of six types of specimens (N=30) were made. Based on the specimens, the setting expansion rate of each one was measured in each time slot of 24 hours, and the surface of the set stone was measured. Results: According to the analysis on setting expansion rate of stone, the setting expansion of the specimen that was created in the way of vacuum mixing at normal mixing ratio was 0.1944% at 120 minutes; the setting expansion of the specimen that was created in the way of vacuum mixing at the mixing ratio which was 40% higher than normal mixing ratio was 0.195% at 120 minutes; the setting expansion of the specimen that was created in the way of mixing with hands at normal mixing ratio and then removing bubbles in vacuum mixer was 0.196% at 120 minutes. Conclusion: The setting expansion rate of each dental stone specimen was significantly different with the lapse of time up to 24 hours(p<.001).

연구목적: 본 연구의 목적은 통상적으로 사용되는 글라스 세라믹과 고분자를 침투시킨 지르코니아 소재로 제작된 코어와 레진시멘트의 굴곡강도 및 결합강도를 비교하여 하이브리드 기술이치과재료의 물리적인 성질에 미치는 영향을 조사하기 위함이다. 연구방법: 본두 가지의 통상적으로 사용되는 세라믹 소재[Vita PM9(GC) and I-JAM(ZC)] 와 다른 두가지 하이브리드 세라믹 소재 [CELTRA Duo(ZRC) and Vita Enamic(RIZ)] 를 평가하였다. 각 그룹의 소재를 선택하여 결합강도와굴곡강도, 그리고scanning electron microscopy(SEM)을이용하여 표면분석을 시행하였다. 도출된 결과데이터는 일원분산분석(One-way ANOVA)을 통해 분석되었으며, 제1종오류의 수준은0.05로 하였다. 연구결과: RIZ 그룹에서 가장 높은 결합강도를 보였으며(p<0.05), ZC 그룹이 가장 낮은 결과를 보였다. 상대적으로굴곡강도는ZC그룹이가장높은수치를나타내었으며, RIZ 그룹이가장취약했다. 연구결론: 하이브리드 기술로 제작된 소재(RIZ 그룹)는 우수한 레진 시멘트와의 결합강도를 보였지만, 그에 비해 굴곡강도는 상대적으로 통상적인 지르코니아 소재보다 비교적 취약한 결과를 보였다.

This study aimed to investigate the influence of hybrid technology on the biaxial flexural strength of conventional ceramic materials and to evaluate whether polymer addition to zirconia more effective bonding than hybridization in glass-ceramics against resin cement. Two conventional ceramics[Vita PM9(GC) and I-JAM(ZC)] and two hybrid ceramics[CELTRA Duo(ZRC) and Vita Enamic(RIZ)] were evaluated. Each group of materials were selected for quantitative bonding performance evaluation and the biaxial flexural strength, and then debonded surfaces were inspected with scanning electron microscopy(SEM). Data were analyzed by a one-way ANOVA test, followed by Tukey’s HSD test(α=0.05). The RIZ group had a significantly higher bond strength than the other groups(p<0.05). ZC showed the lowest mean bond strength values. SEM micrographs showed a sand-blasted ZC surface, whereas RIZ showed an undulation because of the fracture of the bodies of substrate. The flexural strength of ZC was significantly higher than those of all other ceramics evaluated. The flexural strength of RIZ was significantly lower than those of GC, ZRC, and ZC, whereas no significant difference was observed between GC and ZRC Ceramic hybridization with polymers is one of the essential strategies to enhance the bond strength of CAD/CAM ceramics to resin cement. Not all hybrid ceramics display the same quality of bonding performance; however RIZ have lower mechanical strength when tested with the biaxial bending method.

Purpose:The increased aesthetic requirements and demands of patients have resulted in the developments of coloring liquid for zirconia. Methods: In this study, zirconia block was dipped into Fe(NO3)3solution, which showed a color and then concentration of Fe(NO3)3and zirconia's color and physical properties depending on the dipping time were observed and compared with exclusive coloring solutions. As the result, the following conclusions were obtained. Results: When compared with the specimens that were colored using exclusive solutions, L* value rose overall depending on the concentration of Fe(NO3)3and a* value was red in the form of (+) in all the specimens. Also, b* value was in the form of (+) at 0.5 to 1 ßfl, but was in the form of (-) at 1.5 to 2 ßfl. The dipping time did not highly influence L* value, but a* value and b* value were directly opposite to the specimens, which were not colored, except the sample that was dipped for only 2 seconds. When compared with exclusive coloring solutions, Fe(NO3)3had the most similar color at 0.5 to 1 ßfl and the longer the coloring time, the higher the rate of color change became. In relation to the density change depending on the addition of Fe(NO3)3, there was the lowest density at 2 ßfl and the density was increased in the specimens that were not colored. Conclusion: These results show that Fe(NO3)3solution can be used to make colored zirconia. It is expected that newly made colored zirconia can be used in clinical practice because the colored zirconia not only possesses the mechanical properties that all ceramic core material should have but also was biocompatible to a living cells.

Purpose:This study was to evaluate the effect of coloring liquids on the shear bond strength between zirconia and veneering ceramic. Methods: Zirconia(15 mm in diameter, 2.5 mm in thickness; n=40) used in the experiment were divided into 5 groups depending on the coloring liquid. Each specimen were polished using a polishing machine(LaboPol-2,Struers, UK). A cylinder of veneering porcelain(6 mm in diameter, 3 mm in thickness) was fabricated and fired on zirconia surfaces. The shear bond strength was measured using a universal testing machine(Model 4302, Instron,USA). All data were analyzed statistically using a one-way ANOVA and Tukey s multiple comparisons test. After the shear bond test, fracture surfaces were examined by SEM. Results: Colored zirconia showed a higher shear bonding strength than that of uncolored zirconia except for colored zirconia immersed in Zirkonzahn coloring liquid. In particular, colored zirconia immersed in Kuwotech coloring liquid showed the highest shear bond strength. After the shear bond test, mixed failure patterns were mainly observed in the failure between zirconia and veneering ceramic. Conclusion: Coloring liquid enhanced the shear bond strength zirconia and veneering ceramic than uncolored zirconia.

Purpose:This research is conducted for better clinical test of Zirconia as we find out the fracture strength difference of Zirconia on cement gaps of full Crown that made use of Zirconia which is somewhat being used in recent dental technology. Methods: We produced each nine of Zirconia Crown of Zirconia fracture cement gaps A group(0.03 mm), B group(0.05 mm), C group(0.08 mm) on cement gaps by use of CAD/CAM, and compared the results. We could end up getting conclusions as following. Results: There was fracture strength difference per cement gaps but no impact(P<0.05). There was difference between 1.962 0.259 from group A and 2.005 0.367 from group B, but no impact(P<0.05). There was difference between 1.962 0.259 from group A and 2.478 0.331 from group C, but it s hard to be considered as an impact(P<0.05). Conclusion: Because of the hight pressure 0.08 mm is fractured and Margin has a lot of empty space due to gap for 0.08 mm. To identify the difference between 0.08 mm and 0.05 mm, 0.08 mm is selected as a gap. Therefore when it comes to using 0.05 mm authentically 0.05 mm is quite practical to use as a gap.

Purpose:The purpose of this study were to analysis of marginal adaptation of metal cores fabricated by selective laser sintering. Methods: Main model was prepared and ten stone models were fabricated. Ten single metal cores were fabricated by selective laser sintering(SLS group) and another ten single metal cores using lost wax technique and casting method were manufactured(CAST group). The marginal adaptation of metal cores were analysis using by the silicone replica technique. Silicone replicas were sectioned two times. The marginal adaptations were measured using by digital microscope. Statistical analyses was performed with independent t-test(•·=0.05). Results: Means of marginal adaptations were 90.3 ß­ for SLS group and 65.1 ß­ for CAST group. Two groups were statistically significant differences (p < 0.05). Conclusion: Marginal adaptation of metal cores fabricated by selective laser sintering were ranged within the clinical recommendation.

Purpose:This study investigated perception and plan of dental technologists regarding the old age and retirement for them to enjoy stable old age. Methods: Dental technologists working in Seoul, Incheon, and Gyeonggido were asked to fill out a selfadministered questionnaire, and a total of 200 copies were used for analysis. The collected data were statistically analyzed by using SPSS 22.0(Statistical Package for Social Sciences. Chicago, IL, USA) (a=0.05). In order to compare perception toward old age preparation among the subjects, a Chi-square test was performed, and, to investigate the level of preparedness for old age according to general characteristics, t-test was performed. Results: In the analysis of the old age preparedness by age, there was a significant difference in financial preparation, Asset identification, use of retiring allowance, information gathering, senior town home, and stability (p<0.05). To the questions regarding perception toward retirement, the majority of the subjects (60.5%) answered they had thought about retirement, and many (23.9%) of them attributed the reason to job stress (23.9%). Regarding old age preparedness according to workplace, there was a significant difference in use of retirement allowance and education for old age preparedness between general dental laboratories and general hospitals (p<0.05). Conclusion: It is believed that, for preparation of dental technologists for stable old age, in addition to their personal effort, it is important to provide social support and practical measures to ensure welfare and retirement.

Purpose:The purpose of this study was to investigate the cognition of denture fabrication activities and its cost in National Health Insurance for elderly denture. Methods: A self-administered questionnaire was completed by 41 dental laboratories’ owner who was research subjects of HIRA(Health Insurance Review & Assessment Service)’s policy research for elderly denture in 2011. The questionnaire consisted of general characteristics of the subjects, dental technicians’ knowledge of national health insurance coverage of elderly denture, job-related changes after national health insurance coverage of elderly denture including validity of denture fabrication activity classification and the cost for each service. Each question was measured by Likert 5 point scale or frequency. The collected data were analyzed by SPSS 16.0. Results: Most of the research subjects had been fabricating national health insurance coverage denture(92.7%), also had ample knowledge of national health insurance coverage denture for elderly. Job-related changes after national health insurance coverage of elderly denture revealed marginal differences in the quality. The validity of fabrication activity classification of resin based complete denture was 3.71±1.023 by Likert 5 point scale. Conclusion: The goal of national health insurance for elderly denture is to promote elderly’ s health and well-being. To fabricate denture is a very important part of the denture treatment. For this reason, denture fabrication activity classification and the cost analysis plan should be duly reflected in the policy of national health insurance for elderly denture.

Purpose: The intention of the study is to reveal the factors that influence the safety-behavior and safety-accident of the students of dental laboratory science. We intend to use the study as a basic data of searching effective ways to heighten the safety-behavior of clinical training and to prevent safety-accident. Methods: The survey was conducted on dental technology students. The collected data was analyzed by the statistical program SPSS 21.0. The results were analyzed by reliability, frequency, t-test, correlation, multiple regression. To test for significance on each item, p<0.05 has been decided as a standard. Results: The results of the study showed that the safety of the students was influenced by the school year, the leader of clinical training, clinical training environment and the experience of safety education. The safety-accident turned out to be influenced by the school year of the student and the safety behavior. Conclusion: Active leader of clinical training, clinical training environment that enables the safety-behavior, and the offering of the systematic safety education were the most important factors to heighten the safety behavior of the students and prevent the safety-accident. These factors were expected to not only induce the safety-behavior but also prevent the safety-accident as well.