• The Journal of Korean Academy of Prosthodontics
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• v.50 no.3
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• pp.156-161
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• 2012

Purpose: This study was conducted to obtain difference in fracture strength according to the diameter of one-body O-ring-type of mini implant fixture, to determine the resistance of mini implant to masticatory pressure, and to examine whether overdenture using O-ring type mini implant is clinically usable to maxillary and mandibular edentulous patients. Materials and methods: For this study, 13 mm long one body O-ring-type mini implants of different diameters (2.0 mm, 2.5 mm and 3.0 mm) (Dentis, Daegu, Korea) were prepared, 5 for each diameter. The sample was placed at $30^{\circ}$ from the horizontal surface on the universal testing machine, and off-axis loading was applied until permanent deformation occurred and the load was taken as maximum compressive strength. The mean value of the 5 samples was calculated, and the compressive strength of implant fixture was compared according to diameter. In addition, we prepared 3 samples for each diameter, and applied loading equal to 80%, 60% and 40% of the compressive strength until fracture occurred. Then, we measured the cycle number on fracture and analyzed fatigue fracture for each diameter. Additionally, we measured the cycle number on fracture that occurred when a load of 43 N, which is the average masticatory force of complete denture, was applied. The difference on compressive strength between each group was tested statistically using one-way ANOVA test. Results: Compressive strength according to the diameter of mini implant was $101.5{\pm}14.6N$, $149{\pm}6.1N$ and $276.0{\pm}13.4N$, respectively, for diameters 2.0 mm, 2.5 mm and 3.0 mm. In the results of fatigue fracture test at 43 N, fracture did not occur until $2{\times}10^6$ cycles at diameter 2.0 mm, and until $5{\times}10^6$ cycles at 2.5 mm and 3.0 mm. Conclusion: Compressive strength increased significantly with increasing diameter of mini implant. In the results of fatigue fracture test conducted under the average masticatory force of complete denture, fracture did not occur at any of the three diameters. All of the three diameters are usable for supporting overdenture in maxillary and mandibular edentulous patients, but considering that the highest masticatory force of complete denture is 157 N, caution should be used in case diameter 2.0 mm or 2.5 mm is used.

• The Journal of Korean Academy of Prosthodontics
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• v.50 no.2
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• pp.92-98
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• 2012

Purpose: The aim of this study was to evaluate the effects of different abutment materials on abutment screw loosening and settling-down effect in conical connection type implant system. Materials and methods: Three types of abutment, cementation, gold UCLA, and metal UCLA abutment were used. Two UCLA groups were fabricated in a similar pattern to cementation abutment. Type III gold alloy and Nickel-Chromium alloy was used for casting gold UCLA abutment and metal UCLA abutment, respectively. Fixture and abutment were tightened to 30 Ncm by using digital torque controller and re-tightening was conducted with same force after 10 minutes. Digital torque gauge was used to measure loosening torque and fixture/abutment length was measured by digital micrometer. Dynamic loads between 25 N and 250 N were applied with $0^{\circ}$ angle to the abutment axis. After loading, fixture/abutment length was re-measured and amount of settlement was calculated. Loosening torque value was also measured for comparison Results: All three groups showed significant differences of length when comparing before and after loading, but there was no significant difference of settling amount in all groups. Loosening torque values were significantly decreased when comparing before and after loading in all groups($P$<.05). However, there was no significant difference in loss of loosening torque values when compared to groups. Conclusion: In internal conical connection type implants, dynamic load affected on settlement and loosening torque of implant, but there was no differences between abutments materials. Likewise gold UCLA abutment, metal UCLA abutment might be able to withstand functional load.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.6
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• pp.1479-1489
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• 1995

In this study, tensile strength and modulus were evaluated for a filament wound ring specimen by split disk test and compared with the theoretical values obtained by the rule of mixtures. The circumferentially wound ring specimens were prepared from 4 types of material systems. The results showed that the measured strengths of the composite systems were considerably lower than the theoretical values due to the local bending stresses around the split disk edges. for the measurement of elastic moduli of the filament wound ring specimens, the effect of friction on the strain of the ring must be taken into account. But the effect of friction between the split disk fixture and the ring specimen can be eliminated by averaging the moduli for loading and unloading state with maintaining the same crosshead rates. The measured elastic moduli of ring specimens showed very good agreement with the theoretical values.

• Advanced Composite Materials
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• v.16 no.2
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• pp.167-180
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• 2007

The tensile strength of unidirectional carbon fiber reinforced plastics under a high strain rate was experimentally investigated. A high-strain-rate test was performed using the tension-type split Hopkinson bar technique. In order to obtain the tensile stress-strain relations, a special fixture was used for the impact tensile specimen. The experimental results demonstrated that the tensile modulus and strength in the longitudinal direction are independent of the strain rate. In contrast, the tensile properties in the transverse direction and the shear properties increase with the strain rate. Moreover, it was observed that the strain-rate dependence of the shear strength is much stronger than that of the transverse strength. The tensile strength of off-axis specimens was measured using an oblique tab, and the experimental results were compared with the tensile strength predicted based on the Tsai-Hill failure criterion. It was concluded that the tensile strength can be characterized quite well using the above failure criterion under dynamic loading conditions.

• Proceedings of the Korean Nuclear Society Conference
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• 1997.05b
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• pp.515-519
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• 1997

The purpose of this study is to reduce the fast neutron fluence at the reactor pressure vessel(RPV) and to provide a basis for plant-life extension. In this study, different neutron absorbers were employed in the core outer assemblies of Kori Unit 1 Cycle 14. The modified assemblies were used to calculate fast neutron fluence at the RPV and to evaluate reduction of outer assembly power and total power in core. By comparison with the case of no suppression fixture, the fast neutron fluence of a case with two rows stainless steel around the assembly with natural uranium pins is decreased by 85.8%. It is noted that the modification of outer assembly is more efficient than the previous low leakage loading pattern (LLLP) applied to Kori Unit 1. Also, compared fast neutron fluence in Cycle 1 with Cycle 14, fast neutron fluence at the RPV between Cycle 1 and Cycle 14 is not significantly different. It is found that LLLP applied to the Kori Unit 1 has not contributed to fast neutron fluence reduction at the RPV.

• The Journal of Korean Academy of Prosthodontics
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• v.44 no.2
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• pp.197-206
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• 2006

Statement of problem: One of common problems associated with single teeth dental implant prosthetic is the loosening of screws that retain the implants. Purpose: The maintenance of screw joint stability is considered a function of the preload achieved in the screw when the suggested initial tightening torque is applied. The purpose of this study was to investigate acquired preload after initial clamping torque for estimating screw joint stability. Material and methods: A comparative study on the effect of initial clamping of two types of implant systems with different connections was conducted Three dimensional non-linear finite element analysis is adopted to compare the characteristics of screw preloads and stress distributions between two different types of implant systems composed with abutment, screw, and fixture under the same loading and boundary conditions. Results: 1. When the initial clamping torque of 32Ncm was applied to the implant systems, all types of implants generated the maximum effective stress at the first helix region of screw. 2. Morse taper connection types of implants generate lower stress distributions compared to those by butt joint connection types or implants due to large contact surface between abutment and fixture. 3. The internal types of implant systems with friction grip type implant systems have higher resistance to screw loosening than that of the external types of implant systems since the internal types of implant systems generated larger preload than that generated by the external types for the same tightening moments.

• Journal of Dental Rehabilitation and Applied Science
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• v.22 no.1
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• pp.75-87
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• 2006

The purpose of this study was to investigate the effects of prostheses misfit, cantilever on the stress distribution in the implant components and surrounding bone using three dimensional finite element analysis. Two standard 3-dimensional finite element models were constructed: (1) 3 ITI implant supported, 3-unit fixed partial denture and (2) 3 ITI implant supported, 3-unit fixed partial denture with a distal cantilever. variations of the standard finite element models were made by placing a $100{\mu}m$ or $200{\mu}m$ gap between the fixture, the abutment and the crown on the second premolar and first molar. Total 14 models were constructed. In each model, 244 N of vertical load and 244 N of $30^{\circ}$ oblique load were placed on the distal marginal ridge of the distal molar. von Mises stresses were recorded and compared in the crowns, abutments, crestal compact bones, and trabecular bones. The results were obtained as follows: 1. In the ITI implant system, cement-retained prostheses showed comparatively low stress distributions on all the implant components and fixtures regardless of the misfit sizes under vertical loading. The stresses were increased twice under oblique loading especially in the prostheses with cantilever, but neither showed the effects of misfit size. 2. Under the oblique loading and posterior cantilever, the stresses were highly increased in the crestal bones around ITI implants, but effects of misfit were not shown. Although higher stresses were shown on the apical portion of trabecular bones, the effects by misfit were little and the stresses were increased by the posterior cantilever. 3. When the cement loss happened in the ITI implant supported FPD with misfit, the stresses were increased in the implant componets and supporting structures.

• Journal of Technologic Dentistry
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• v.38 no.3
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• pp.143-149
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• 2016

Purpose: The purpose of this study is to evaluate the effect of two different oblique mechanical loading to occlusal surfaces of cement retained implant on the stress distributions in surrounding bone, using 3-dimensional finite element method. Methods: A 3-dimensional finite element model of a cement retained implant composed of three unit implants, simplified ceramic crown and supporting bone was developed according to the design of ement retained implant for this study. two kinds of surface distributed oblique loads(100 N) are applied to following occlusal surfaces in the single crowns; 1) oblique load on 2 occlusal points(50N for each buccal cusp, 2 buccal cusps exist), 2) oblique load on 4 occlusal points(25N for each buccal and lingual cusp, 2 buccal and 2 lingual cusps exist) Results: The results of the comparison of the stress distributions on surrounding bone are as follows. In the condition of oblique load on 2 occlusal points, VMS was 741.3 Mpa in the M1(Ø$4.0{\times}13mm$) model and 251.2 Mpa in the M2(Ø$5.0{\times}13mm$) model. It means the stress on the supporting bone is decreased. The results of oblique load on 4 occlusal points are similar to this one. Conclusion: Increasing the diameter of the implant fixture is helpful to distribute the stress on the supporting bone. Also, to obtain the structural stability of the supporting bone, it is effective to distribute the load evenly on the occlusal surface of crown in producing single crown implant.

• The Journal of Korean Academy of Prosthodontics
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• v.45 no.2
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• pp.240-249
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• 2007

Statement of problem: A phenomenon of screw-loosening in implant abutment is frequently occurred in a single and multiple implant restoration. Purpose: This study was performed to evaluate an effect of abutment material on screw-loosening before and after a cyclic loading. In a single-tooth implant, different materials of abutment, Type III Gold alloy and Zirconium composite$(ZrO_2/Al_2O_3)$ were used. Material and method: The Gold alloy(Type III) and Zirconium composite$(ZrO_2/Al_2O_3)$ were used to make a superstructure of implant, the one of types of UCLA, Each group was constituted of 5 sample with a 30-degree offset angulated loading platform. The external hexagonal fixture was rigidly hel d in a special holding zig to ensure solid fixation without rotation during the tightening and a cyclic loading. A Titanium-alloy screw was used to connect and controlled to be tighten in 20Ncm torque by a digital torque gauge. A 20 times of consecutive closing/opening cycle were performed to evaluate the immediate torque loss. In 5 sample of each material group, an initial opening torque was recorded during 3 closing/opening cycle, then 2Hz, 200N, 1,000,000 cyclic loadings were performed, then a opening torque was evaluated. Result & Conclusion: 1. In this limited study, titanium alloy screw tightened in 20Ncm, a cold-welding phenomen on was not observed during the 20 times of closing/opening cycle(p=0.11, p=0.18). 2. In titanium alloy abutment screw, repeated opening and closing of the screw caused to progressive decrease of opening torque(p=0.014). 3. The difference in preload of screw between gold alloy abutment and ceramic$(ZrO_2/Al_2O_3)$ abutment was not significant(p=0.78). 4. The difference in torque loss of screw between gold alloy abutment and ceramic$(ZrO_2/Al_2O_3)$ abutment was not significant after 2Hz,200N, 1,000,000 cyclic loading(p=0.92). 5. In titanium alloy abutment screw tightened by 20Ncm, the screw loosening was not significant on each group after 2Hz, 200Ncm, 1,000,000 cyclic loading(p=0.59).

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.11
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• pp.494-500
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• 2019

The purpose of this study was to determine a method to prevent damage during the transfer of loading through optimal design of loading transfer software for an ammunition-carrying armored vehicle. Typically, an ammunition carrier armored car is equipped with an automated charge transfer system. The load is intermittently damaged during the loading of the cargo, and this needs to be improved. The following improvements and verification tests were carried out. As impact speed increased, the loading speed was reduced 60%, and a special fixture utilizing a force gauge was developed and tested. If the maximum current of 11A for the servo controller is output when the load of the conveyor is generated by interference inside the loading tube, there is a possibility of charge breakage. If the maximum current is low, the load cannot be loaded. In the loading test for the ammunition carrier armored car with the actual charge, the improved design was found to be valid, as the load was not damaged and occurred nominally.