• Journal of the Korean GEO-environmental Society
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• v.21 no.7
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• pp.5-16
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• 2020

Currently, the seismic design standards have been strengthened due to the occurrence of the Gyeongju and Pohang earthquake, and seismic performance evaluation of existing facilities is being conducted. It aims to secure a seismic performance effect during earthquakes by improving the micro-pile method, which can be constructed in limited confined places while minimizing damage to existing facilities. The improvement method is to construct all the piles in the square-tray-type plate on the top of the pile by constructing the slope pile in the form of an umbrella around the vertical pile, the main pillar. In this paper, the numerical analysis was performed to analyze the horizontal displacement behavior of an umbrella-type micropile for various real-measurement seismic waves in sandy soil. As a result of numerical analysis, the softer the ground, the better the effect of horizontal resistance of umbrella-type micropile. The horizontal displacement reduction effect was pronounced when the embedded depth was 15 m or more at the same ground strength, and it was found to be effective in earthquakes if it was settled on the ground with an N value of 30 or more. The embedded depth and horizontal displacement suppression effect of the micropile was proportional. Generally, the weaker the ground, the greater the displacement suppression effect. Umbrella-type micropile had a composite resistance effect in which the vertical pile resists the moment and inclined pile resists the axial force.

• Journal of Dental Rehabilitation and Applied Science
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• v.25 no.3
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• pp.225-235
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• 2009

A common procedure of restoration of endodonticlly treated tooth with fiber-reinforced post is followed by core build-up after post cementation. However, this technique is complex and time-consuming. The aim of this study was to compare fracture strength of premolar, restored with various methods of core fabrications on fiber-reinforced posts and casting metal restoration. Forty five freshly extracted human mandibular premolars were obtained and devided into 5 groups acconding to the type of post and methods of core build-up. In Group A, D.T. $Light-post^{(R)}$ were cemented with $DUO-LINK^{TM}$ and then $LIGHT-CORE^{TM}$ was used for core restoration. In Group B, D.T. $Light-post^{(R)}$ and $DUO-LINK^{TM}$ were used for cementing in the postspace, and $DUO-LINK^{TM}$ was used again for core restoration. In Group C, $Light-post^{(R)}$ bonding and the core build-up were performed simultaneously by using $DUO-LINK^{TM}$. In Group D, $LuxaPost^{(R)}$ was bonded by using $LuxaCore^{(R)}-Dual$. Again, $LuxaCore^{(R)}-Dual$ was used for core restoration. In Group E, $LuxaPost^{(R)}$ bonding and the core build-up were performed simultaneously by using $LuxaCore^{(R)}-Dual$. Axial reduction was formed parallelly as possible and 45 degree bevel was made at buccal occlusal surface. Crowns were fabricated and cemented. Each tooth was embedded in self-curing acrylic resin to the level of 2mm below the CEJ. Specimens were fixed on universal testing machin such that the axis of the tooth was at 45 degree inclination to the horizontal plane, and compressive force was applied at a crosshead speed of 1mm/min until failure occurred. The mean fracture strength was the highest in group A followed by descending order in group B, D, E and C. However, there were no statistically significant differences between groups with regard to the fracture strength. The type of the post or build-up methods of the core does not seem to influence the fracture strength.

• The Journal of Korean Academy of Prosthodontics
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• v.51 no.3
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• pp.160-166
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• 2013

Purpose: The purpose of this study was to compare the fracture strength of traditional metal-ceramic crowns and full zirconia crowns according to the occlusal thickness. Materials and methods: A mandibular first molar resin tooth was prepared with 1.5 mm occlusal reduction, 1.0 mm rounded shoulder margin and $6^{\circ}$ taperness in the axial wall. Duplicating the resin tooth, 64 metal dies were fabricated. 48 full zirconia crowns were fabricated using Prettau zirconia blanks by ZIRKONZAHN CAD/CAM and classified into six groups according to the occlusal thickness (0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1.0 mm). 16 metal-ceramic crowns were fabricated and classified into two groups according to the occlusal porcelain thickness (1.0 mm, 1.5 mm). All crowns were cemented on each metal die and mounted in a universal testing machine. The load was directed at the functional cusp of each specimen until catastrophic failure occurred. One-way ANOVA, Tukey multiple comparison test (${\alpha}=.05$) and t-test (${\alpha}=.05$) were used. Results: The results were as follows. 1. The test 1 group (646.48 N) showed the lowest fracture strength (P<.05), and the value of the test 2.3.4.5 groups (866.40 N, 978.82 N, 1196.82 N, 1222.41 N) increased as thickness increased, but no significant difference were found with the groups (P>.05). The value of test 6 group (1781.24 N) was significantly higher than those of the other groups (P<.05). 2. There were no significant differences of the fracture strength of metal ceramic crowns according to occlusal porcelain thickness 1.0 mm (2515.71 N) and 1.5 mm (3473.31 N) (P<.05). Conclusion: Full zirconia crown needs to be 1.0 mm or over in occlusal thickness for the posterior area to have higher fracture strength than maximum bite force.

• The Journal of Korean Academy of Prosthodontics
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• v.46 no.2
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• pp.157-168
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• 2008

Statement of problem: Over the past two decades, implant supported fixed prosthesis have been widely used. However, there are few studies conducted systematically and intensively on the splinting effect of implant systems in mandible. Purpose: The purpose of this study was to investigate the changes in stress distributions in the mandibular implants with splinting or non-splinting crowns by performing finite element analysis. Materials and methods: Cortical and cancellous bone were modeled as homogeneous, transversely isotropic, linearly elastic. Perfect bonding was assumed at all interfaces. Implant models were classified as follows. Group 1: $Br{{\aa}}nemark$ length 8.5mm 13mm splinting type Group 2: $Br{{\aa}}nemark$ length 8.5mm 13mm Non-splinting type Group 3: ITI length 8.5mm 13mm splinting type Group 4: ITI length 8.5mm 13mm Non-splinting type An load of 100N was applied vertically and horizontally. Stress levels were calculated using von Mises stresses values. Results: 1. The stress distribution and maximum von Mises stress of two-length implants (8.5mm, 13mm) was similar. 2. The stress of vertical load concentrated on mesial side of implant while the stress of horizontal load was distributed on both side of implant. 3. Stress of internal connection type was spreading through abutment screw but the stress of external connection type was concentrated on cortical bone level. 4. Degree of stress reduction was higher in the external connection type than in the internal connection type.