• The Journal of Korean Academy of Prosthodontics
• /
• v.52 no.2
• /
• pp.82-89
• /
• 2014

Purpose: The purpose of this study was to observe the change of viscoelastic properties of dental resin cements during polymerization. Materials and methods: Six commercially available resin cement materials (Clearfil SA luting, Panavia F 2.0, Zirconite, Variolink N, RelyX Unicem clicker, RelyX U200) were investigated in this study. A dynamic oscillation-time sweep test was performed with AR1500 stress controlled rheometer at $32^{\circ}C$. The changes in shear storage modulus (G'), shear loss modulus (G"), loss tangent (tan ${\delta}$) and displacement were measured for twenty minutes and repeated three times for each material. The data were analyzed using one-way ANOVA and Tukey's post hoc test (${\alpha}$=0.05). Results: After mixing, all materials demonstrated an increase in G' with time, reaching the plateau in the end. RelyX U200 demonstrated the highest G' value, while RelyX Unicem (clicker type) and Variolink N demonstrated the lowest G' value at the end of experimental time. Tan ${\delta}$was maintained at some level and reached the zero at the starting point where G' began to increase. The tan ${\delta}$and displacement of the tested materials showed similar pattern in the graph within change of time. The displacement of all 6 materials approached to zero within 6 minutes. Conclusion: Compared to other resin cements used in this study, RelyX U200 maintained plastic property for a longer period of time. When it completed the curing process, RelyX U200 had the highest stiffness. It is convenient for clinicians to cement multiple units of dental prostheses simultaneously.

• Journal of the Korean Society of Radiology
• /
• v.12 no.1
• /
• pp.47-52
• /
• 2018

Brain perfusion CT scanning is often employed usefully in clinical conditions as it accurately and promptly provides information about the perfusion state of patients having acute ischemic stroke with a lot of time constraints and allows them to receive proper treatment. Despite those strengths of it, it also has a serious weakness that Lens may be exposed to a lot of dose of radiation in it. In this study, as a way to reduce the dose of radiation to Lens in brain perfusion CT scanning, this researcher conducted an experiment with Bismuth shielding and change of patients' position. TLD (TLD-100) was placed on both lens using the phantom (PBU-50), and then, in total 4 positions, parallel to IOML, parallel to IOML (Bismuth shielding), parallel to SOML, and parallel to SOML (Bismuth shielding), brain perfusion scanning was done 5 times for each position, and dose to Lens were measured. Also, to examine how the picture quality changed in different positions, 4 areas of interest were designated in 4 spots, and then, CT number and noise changes were measured and compared. According to the results of conducting one-way ANOVA on the doses measured, as the significance probability was found to be 0.000, so there was difference found in the doses of radiation to crystalline lenses. According to the results of Duncan's post-hoc test, with the scanning of being parallel to IOML as the reference, the reduction of 89.16% and 89.66% was observed in the scanning of being parallel to SOML and that of being parallel to SOML (Bismuth shielding) respectively, so the doses to Lens reduced significantly. Next, in the scanning of being parallel to IOML (Bismuth shielding), the reduction of 37.12% was found. According to the results, reduction in the doses of radiation was found the most significantly both in the scanning of being parallel to SOML and that of being parallel to SOML (Bismuth shielding). With the limit of the equivalent dose to Lens as the reference, this researcher conducted comparison with the dose to occupational exposure and dose to Public exposure in the scanning of being parallel to IOML and found 39.47% and 394.73% respectively; however in the scanning of being parallel to SOML (Bismuth shielding), considerable reduction was found as 4.08% and 40.8% respectively. According to the results of evaluation on picture quality, every image was found to meet the evaluative standards of phantom scanning in terms of the measurement of CT numbers and noise. In conclusion, it would be the most useful way to reduce the dose of radiation to Lens to use shields in brain perfusion CT scanning and adjust patients' position so that their lens will not be in the field of radiation.

• Radiation Oncology Journal
• /
• v.15 no.3
• /
• pp.207-213
• /
• 1997

Purpose : Intracranial germinoma is the most radiocurable tumor of theprimary intracranial neoplasm. But, the optimum radiation dose and target volume remain controversial In this retrospective study, we analysed the spreading pattern at presentation and the pattern of the failure and survival of intracranial germinoma, Materials and Methods : From 1989 to 1996, 23 Patients were treated for intracranial germinoma at Department of Radiation Oncology, Twenty-one Patients were treated at their initial Presentation and 2 Patients were treated for recurrent disease. Six patients had multiple tumor masses on MRI and 7patients had ventricular seeding on MRI. The examination of cerebrospinal fluid cytology was done in 15 patients and 3 out of 15 patients had positive cerebrospinal cytology. In tumor marker study of $\alpha-FP\;and\;\beta-hCG$, 6 patients had mildly elevated $\beta-hCG$ in serum or cerebrospinal fluid. Twentyone Patients were treated with whole craniospinal axis irradiation and 2 Patients were given whole ventricular radiation therapy. The total dose was ranged between 4500cGy and 5600cGy to primary tumor site (median 5580cGy) Dose to the entire ventricular system ranged from 1980cGy to 3960 cGy (median 2700cGy) and dose to the spinal axis ranged from 2160cGy to 3900cGy (median 2700cGy) Results : Of 23 patients, 21 Patients are alive without evidence of diseasefor median 4 years follow-up. One Patient who had markedly elevated $\alpha-FP\;and\;\beta-hCG$, suffered from Persistent disease after radiation therapy and received 2 cycles of chemotherapy. She died 9 months after chemotherapy One patient who developed ventricular seeding after gamma-knife was treated with whole craniospinal irradiation, he died after 1 year due to probably brain necrosis. The hematologic toxicity of 3 or 4 grade were seen in 7 patients and patient's endocrinologic dysfunction was not deteriorated after radiation therapy. One patient had been treated with growth hormone replacement due to short stature. Conclusions : This retrospective study has confirmed the excellent result of radiation therapy in intracranial germinoma. The complication rate during or after radiation therapy is considered within acceptable range. ft is necessary to further investigate the optimal dose and treatment volume of radiation therapy. The role of chemotherapy in the treatment of intracranial germinoma should be further investigated.

• Journal of Animal Science and Technology
• /
• v.51 no.4
• /
• pp.329-336
• /
• 2009

The objective of this study was to investigate the relationship between measurements of color and water-holding capacity (WHC) in pork loin. A total of 419 pork loins were sampled from crossbred (Landrace$\times$Jeju native black pig) F2 pigs at a commercial slaughter house. Meat color measurements (CIE $L^*$, $a^*$, $b^*$), chroma ($C^*$) and hue angle (h) were measured with the Minolta Chromameter and WHC was measured by filter paper fluid, drip loss and cooking loss. Also pH, moisture content and crude fat content were measured at 24 hr postmortem. CIE $L^*$, $b^*$ and h values had positive correlation with drip loss (r=0.52, 0.42), but CIE $a^*$ and $C^*$ values were not related to drip loss. Results showed that CIE $L^*$, $b^*$, and h color system was better than CIE $L^*$, $a^*$, $b^*$ color system to predict WHC, especially drip loss. pH was negatively correlated to drip loss (-0.42) and CIE $L^*$ (-0.67). Although CIE $L^*$ and pH were correlated to drip loss, the accuracy of their estimates for drip loss was 27% and 17%, respectively. Consequently, it was confirmed that meat color and WHC were not perfectly related and suggested that CIE $L^*$, $b^*$, and h color space should not be used independently to predict WHC of pork loin.

• Restorative Dentistry and Endodontics
• /
• v.31 no.6
• /
• pp.477-484
• /
• 2006

The purposes of this study were to compare the apical terminus width of simulated curved root canal prepared with three NiTi file systems used by undergraduates for evaluation the effects of flute angle and pitch or radial land on reducing screw-in effect and to determine more safe NiTi file system for inexperienced operators. Fifty inexperienced undergraduate students prepared 150 simulated curved root canals in resin blocks with three NiTi file systems ; ProFile$^{(R)}$, Hero Shaper$^{(R)}$, K3$^{TM}$. The electric motor set at a speed of 300 rpm and torque of 30 in a 16 : 1 reduction handpiece was used. The simulated root canal was prepared to ISO #25 sizes with each file system. The scanned images of pre- and post-instrumented canal of resin block were superimposed. To evaluate the screw-in effect of three NiTi file systems, apical terminus width of root canal was measured from superimposed images and statistical analysis was performed. There were significant differences in three NiTi flle systems. ProFile$^{(R)}$ had significantly smaller width than Hero Shaper$^{(R)}$ and K3$^{TM}$"" (P < 0.05), but no significant difference was observed between K3$^{TM}$ and Hero Shaper$^{(R)}$. Under the condition of this study, active file system (Hero SHaper$^{(R)}$, K3$^{TM}$) with variable pitch and helical angle had more screw-in effect than passive file system (ProFile$^{(R)}$) with constant pitch and helical angle. It seems that the radial lands play more important role in reducing screw-in effect.

• Restorative Dentistry and Endodontics
• /
• v.33 no.3
• /
• pp.169-176
• /
• 2008

The purpose of this study was to evaluate the effect of thickness, filling methods and curing methods on the polymerization of dual cured core materials by means of microhardness test. Two dual cured core materials, MultiCore Flow (Ivoclar Vivadent AG, Schaan, Liechtenstein) and Bis-Core (Bisco Inc., Schaumburg, IL, USA) were used in this study. 2 mm (bulky filled), 4 mm (bulky filled), 6 mm (bulky and incrementally filled) and 8 mm (bulky and incrementally filled)-thickness specimens were prepared with light cure or self cure mode. After storage at $37{\circ}C$ for 24 hours, the Knoop hardness values (KHN) of top and bottom surfaces were measured and the microhardness ratio of top and bottom surfaces was calculated. The data were analyzed using one-way ANOVA and Scheffe multiple comparison test, with ${\alpha}$= 0.05. The effect of thickness on the polymerization of dual cured composites showed material specific results. In 2, 4 and 6 mm groups, the KHN of two materials were not affected by thickness. However, in 8 mm group of MultiCore Flow, the KHN of the bottom surface was lower than those of other groups (p < 0.05). The effect of filling methods on the polymerization of dual cured composites was different by their thickness or materials. In 6 mm thickness, there was no significant difference between bulk and incremental filling groups. In 8 mm thickness, Bis-Core showed no significant difference between groups. However, in MultiCore Flow, the microhardness ratio of bulk filling group was lower than that of incremental filling group (p < 0.05). The effect of curing methods on the polymerization of dual cured composites showed material specific results. In Bis-Core, the KHN of dual cured group were higher than those of self cured group at both surfaces (p < 0.05). However, in MultiCore Flow, the results were not similar at both surfaces. At the top surface, dual cured group showed higher KHN than that of self cured group (p < 0.05). However, in the bottom surface, dual cured group showed lower value than that of self cured group (p < 0.05).

• Journal of the Korean Society of Food Science and Nutrition
• /
• v.45 no.11
• /
• pp.1673-1680
• /
• 2016

The purpose of this study was to examine how customer orientation (CO) reduces employee stress to customers (CSS). As emotional labor strategies [surface acting (SA) and deep acting (DA)] may mediate a role between CO and CSS, we verified multiple parallel mediator roles of SA and DA between CO and CSS. Our survey was administered to 323 school foodservice employees in Daegu and Gyeongbuk. The results show that CO increased DA but did not decrease SA, and SA had a positive effect on CSS while DA did not influence CSS. These results did not support the parallel multiple mediator model. We conducted post-hoc model modification and proposed the serial multiple mediator model as a modified model. As a result, CO increased DA, DA reduced SA, and SA showed a positive relation with CSS. This double mediating effect through DA and SA between CO and CSS was significant. Based on these results, we found that CO did not have a direct effect on SA and CSS. DA did not directly reduce CSS while CO reduced SA and CSS through DA indirectly. DA had a negative effect on CSS through SA indirectly. Finally, implications and limitations of this are discussed.

• Restorative Dentistry and Endodontics
• /
• v.34 no.2
• /
• pp.145-153
• /
• 2009

The purpose of this study was to evaluate the effect of instrument compliance on the polymerization shrinkage stress measurements of dental composites. The contraction strain and stress of composites during light curing were measured by a custom made stress-strain analyzer, which consisted of a displacement sensor, a cantilever load cell and a negative feedback mechanism. The instrument can measure the polymerization stress by two modes: with compliance mode in which the instrument compliance is allowed, or without compliance mode in which the instrument compliance is not allowed. A flowable (Filtek Flow: FF) and two universal hybrid (Z100: Z1 and Z250: Z2) composites were studied. A silane treated metal rod with a diameter of 3.0 mm was fixed at free end of the load cell, and other metal rod was fixed on the base plate. Composite of 1.0 mm thickness was placed between the two rods and light cured. The axial shrinkage strain and stress of the composite were recorded for 10 minutes during polymerization. and the tensile modulus of the materials was also determined with the instrument. The statistical analysis was conducted by ANOVA. paired t-test and Tukey's test (${\alpha}<0.05$). There were significant differences between the two measurement modes and among materials. With compliance mode, the contraction stress of FF was the highest: 3.11 (0.13). followed by Z1: 2.91 (0.10) and Z2: 1.94 (0.09) MPa. When the instrument compliance is not allowed, the contraction stress of Z1 was the highest: 17.08 (0.89), followed by FF: 10.11 (0.29) and Z2: 9.46 (1.63) MPa. The tensile modulus for Z1, Z2 and FF was 2.31 (0.18), 2.05 (0.20), 1.41 (0.11) GPa, respectively. With compliance mode. the measured stress correlated with the axial shrinkage strain of composite: while without compliance the elastic modulus of materials played a significant role in the stress measurement.

• The Journal of Korean Academy of Prosthodontics
• /
• v.57 no.2
• /
• pp.127-133
• /
• 2019

Purpose: The purpose of present study was to investigate fracture strength and mode of failure of endodontically treated teeth restored with metal cast post-core system, prefabricated fiber post system, and newly introduced polyetherketoneketone (PEKK) post-core system. Materials and methods: A total of 21 mandibular premolar were randomly grouped into 3 groups of 7 each according to the post material. Group A was for metal cast post core; Group B for prefabricated glass fiber post and resin core; and Group C for milled PEKK post cores. All specimens were restored with metal crown. The fracture strength of each specimen was measured by applying a static load of 135-degree to the tooth at 2 mm/min crosshead speed using a universal testing machine. After the fracture strength measurement, the mode of failure was observed. The results were analyzed using Kruscal-Wallis test and post hoc Mann-Whitney U test at confidence interval ${\alpha}=.05$. Results: Fracture resistance of PEKK post core was lower than those of cast metal post and fiber reinforced post with composite resin core. In the aspect of fracture mode most of the root fracture occurred in the metal post core, whereas the post detachment occurred mainly in the fiber reinforced post. In the case of PEKK post core, teeth and post were fractured together. Conclusion: It is necessary to select appropriate materials of post for extensively damaged teeth restoration and clinical application of the PEKK post seems to require more research on improvement of strength.

• Journal of Intelligence and Information Systems
• /
• v.27 no.1
• /
• pp.177-190
• /
• 2021

Due to the development of the fourth industrial revolution technology, efforts are being made to improve areas that humans cannot handle by utilizing artificial intelligence techniques such as machine learning. Although on-demand production companies also want to reduce corporate risks such as delays in delivery by predicting total production time for orders, they are having difficulty predicting this because the total production time is all different for each order. The Theory of Constraints (TOC) theory was developed to find the least efficient areas to increase order throughput and reduce order total cost, but failed to provide a forecast of total production time. Order production varies from order to order due to various customer needs, so the total production time of individual orders can be measured postmortem, but it is difficult to predict in advance. The total measured production time of existing orders is also different, which has limitations that cannot be used as standard time. As a result, experienced managers rely on persimmons rather than on the use of the system, while inexperienced managers use simple management indicators (e.g., 60 days total production time for raw materials, 90 days total production time for steel plates, etc.). Too fast work instructions based on imperfections or indicators cause congestion, which leads to productivity degradation, and too late leads to increased production costs or failure to meet delivery dates due to emergency processing. Failure to meet the deadline will result in compensation for delayed compensation or adversely affect business and collection sectors. In this study, to address these problems, an entity that operates an order production system seeks to find a machine learning model that estimates the total production time of new orders. It uses orders, production, and process performance for materials used for machine learning. We compared and analyzed OLS, GLM Gamma, Extra Trees, and Random Forest algorithms as the best algorithms for estimating total production time and present the results.