• The Journal of Korean Academy of Prosthodontics
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• v.38 no.6
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• pp.765-781
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• 2000

The purpose of this study was to compare the screw loosening characteristics of three avail-able cementation type abutments: one-piece cementation type abutment; two-piece cementation type abutment using titanium abutment screw; two-piece cementation type abutment using gold abutment screw. Two implant supported three-unit superstructures were fabricated using a pair of 3 kinds of abutments for each experimental model. Cyclic loading was applied on the specimen, and made to stop when the superstructure showed movement over threshold range. The loaded cycle was counted until the machine stopped. Frequency analysis was done to measure the change of natural frequency before and after the application of cyclic load and to find the effect of screw loosening on the change of natural frequency. The specimen assembly was modeled to perform the finite element analysis to see the distribution of the stress induced by the application of preload over the screw joint and to compare the pattern of the distribution of stress induced by the external force with the change of the preload condition. The following results were obtained: 1. The failure loading cycle of two-piece cementation type abutment using gold screw was significantly greater than those of the other groups. 2. One-piece cementation type abutment applied to multi-unit restoration case did not show greater resistance to screw loosening compared to two-piece cementation type abutments. 3. Frequency analysis showed decrease in natural frequency when screw loosening occured.

• The Journal of Korean Academy of Prosthodontics
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• v.45 no.3
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• pp.345-353
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• 2007

Statement of problem. Implant abutment screw joints tend to loosen under clinical conditions. Abutment screw loosening results in loss of preload in function. Purpose. Anti-rotational inner post screw (ARIPS) systems were compared with conventional abutment screws to reduce screw loosening. Reverse torque values were evaluated. Material and methods. 32 implant assemblies (Warentec, Co, Ltd, Seoul, Korea) were organized as the 30-Ncm-torque conventional groups and 30-Ncm-torque ARIPS groups in external and internal system. The specimens were tested to 106 cycles at a load of 200N. Preload reverse torque, postload reverse torque, and the ratio of postload reverse torque to preload reverse torque were evaluated. The data were analyzed with unpaired t-test in external and internal systems. Results. In the ratio of postload reverse torque to preload reverse torque, the ARIPS groups showed significant differences than the conventional screw group in both external and internal system. Conclusion. Within the limitations of this study, abutment screw loosening was effectively reduced using ARIPS system.

• Journal of Korean Tunnelling and Underground Space Association
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• v.5 no.3
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• pp.217-226
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• 2003

This study is focused on the finding out load transfer mechanism in the ground near the tunnel during tunnel excavation in the jointed sandy ground. Laboratory model tests were performed on various cases of the overburden heights above tunnel crown, location, and degree of discontinuity planes. For model tests, a movable plate was installed in the midst of the bottom of sandy ground. This plate, moving downwards, was intended to model the stress relaxation during tunnel excavation. The load transfer was measured at the fixed separated bottom plates adjacent to the movable plate. As the result, the loosening zone and the load-transfer form around the tunnelling site were affected by the overburden height and the characteristics of discontinuous planes. And large loosening zone was developed along the discontinuous planes which were close to the tunnel.

• Tunnel and Underground Space
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• v.12 no.2
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• pp.107-114
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• 2002

It is the common practice to over design the reinforcement for the secondary tunnel lining due to the lack of rational insight into the ground loosening loads. and due to the conservative application of the empirical design methods. The main loads of the secondary lining are the ground Loosening loads and the ground water pressure, and the ground load is critical in the reinforcement design of the secondary lining in the case of drained tunnel. If the external load is absent around a tunnel, the reasons of the load far secondary tunnel lining are the deterioration of the primary supports such as shotcrete, steel rib, and rockbolts. Accordingly, the analysis method considering the ground-primary supports-secondary lining interaction should be required tar the rational design of the secondary tunnel lining. In this paper, the interaction was conceptually described by the simple mass-spring model and the load transfer from the ground and primary supports to the secondary lining is showed by the ground-primary supports-secondary lining reaction curves fur the theoretical solution of a circular tunnel. And also, the application of this proposed model to numerical analysis is verified in order to check the potential far the tunnel with the complex analysis conditions.

• Journal of Dental Rehabilitation and Applied Science
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• v.19 no.2
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• pp.125-137
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• 2003

The use of screw-retaind prosthesis on an osseointegrated implant is a popular treatment modality offering relative ease in the removal of the restoration. One of the complications associated with this modality is the loosening of the abutment and coping screws. Loosening of the screws results in patient dissatisfaction, frustration to the dentist and, if left untreated, component fracture. There are several factors which contribute to the loosening of implant components which can be controlled by the restorative dentist and lab technician. This article offers pratical solutions to minimize this clinical problem and describes the factors involved in maintaining a stable screw joint assembly. To avoid joint failure, adherence to specific clinical, as well as mechanical, parameters is critical. With respect to hardware, optimal tolerance and fit, minimal rotational play, best physical properties, a predictable interface, and optimal torque application are mandatory. In the clinical arena, optimal implant distribution; load in line with implant axis; optimal number, diameter, and length of implants; elimination of cantilevers; optimal prosthesis fit; and occlusal load control are equally important.

• The Journal of Advanced Prosthodontics
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• v.10 no.6
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• pp.415-421
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• 2018

PURPOSE. This study investigated the effects of abutment screw lengths on screw loosening and removal torque in external connection implants after oblique cyclic loading. MATERIALS AND METHODS. External connection implants were secured with abutment screws to straight abutments. The abutment-implant assemblies were classified into seven groups based on the abutment screw length, with each group consisting of five assemblies. A cyclic load of 300 N was applied at a $30^{\circ}$ angle to the loading axis until one million cycles were achieved. Removal torque values (RTVs) before and after loading, and RTV differences were evaluated. The measured values were analyzed using repeated measures of analysis of variance with the Student-Newman-Keuls multiple comparisons. RESULTS. All assemblies survived the oblique cyclic loading test without screw loosening. There was a significant decrease in the RTVs throughout the observed abutment screw lengths when the abutment-implant assemblies were loaded repeatedly (P<.001). However, the abutment screw length did not show significant difference on the RTVs before and after the experiment when the abutment screw length ranged from 1.4 to 3.8 mm (P=.647). CONCLUSION. Within the limit of this experiment, our results indicate that the abutment screw length did not significantly affect RTV differences after oblique cyclic loading when a minimum length of 1.4 mm (3.5 threads) was engaged. These findings suggest that short abutment screws may yield stable clinical outcomes comparable to long screws in terms of load resistance.

• Journal of Korean Tunnelling and Underground Space Association
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• v.4 no.1
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• pp.71-78
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• 2002

In this study, the influence of the presence of discontinuity planes on the load transfer mechanism and the pattern of loosening zone was studied based on the laboratory test. The trap-door and the reaction plates are installed as the bottom plane of the model box. The vertical discontinuity plane is installed in the dry sand. Various overburden heights and locations of discontinuity planes are applied as major factors in this study. The results show that at higher overburden heights over about 1.5 times the excavation width, the ratio of the transferred stress to the insitu stress converges to a certain value even if the overburden height increases further. The results also show that the discontinuity plane gives relatively larger influence on the load transfer mechanism, that produces the unsymmetrical load concentration, when the discontinuity plane locates within the tunnel width. When the discontinuity plane locates outside the tunnel width, the unsymmetrical load concentration is reduced considerably.

• Journal of Dental Rehabilitation and Applied Science
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• v.35 no.3
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• pp.132-142
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• 2019

Purpose: The purpose of this finite element analysis study is to introduce the novel Lock screw system and analyze its mechanical property to see if it can prevent abutment screw loosening. Materials and Methods: The Lock screw is a component tightened on the inside of the implant abutment which applies compressive force to the abutment screw head. To investigate the effect, modeling was done using CAD program and it was analyzed by finite element analysis under various load conditions. First, the preload was measured according to the tightening torque of the abutment screw then it was compared with the theoretical value to verify the analytical model. The validated analytical model was then divided into those with no external load and those with 178 N, and the tightening torque of the lock screw was changed to 10, 20, 30 Ncm respectively to examine the property of stress distribution on the implant components. Results: Using Lock screw under various loading conditions did not produce equivalent stresses beyond the yield strength of the implant components. In addition, the axial load was increased at the abutment-abutment screw interface. Conclusion: The use of Lock screw does not exert excessive stress on the implant components and may increase the frictional force between the abutment-abutment screw interface, thus it is considered to prevent loosening of the abutment screw.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.3
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• pp.1117-1121
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• 2011

The movable bracket structure, which is an apparatus for supplying electric power to a running electric locomotive, is applied by a repeated load during the passage of the electric locomotive. Such a repeated load becomes an excitation source that causes screws constituting the movable bracket structure to be loosened. This study was conducted on the causes and countermeasures of the bolt loosening caused by the repeated vibration using a computer simulation. As the result, a simulation model was constructed to enable the dynamic analysis of the movable bracket structure. It could be found that the principal excitation frequency range for the bolt loosening of the movable bracket structure was less than 200 Hz. In addition, the bolts are prevented from being loosened by increasing stiffness of H beams. The vibration mode of a lower band bracket is found to be triggered in a frequency range between 300 and 600 Hz. And the increase in stiffness of the lower band bracket exhibits the effect to avoid the bolt loosening at a frequency range of 200 Hz or more.

• Journal of the Korean Geotechnical Society
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• v.30 no.4
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• pp.65-80
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• 2014

This study conducted Trapdoor tests with actual tunnel shape, investigated the mechanical behavior of ground and loosening load on tunnels, and evaluated the mechanism of progressive failure by numerical simulation. The loosening load sharply decreased initially, but it generally increased and reached the stabilized level exhibiting the arching effect, and loose sand showed relatively higher values than those of dense sand. The shear band started from the tunnel shoulder with $63^{\circ}$ (loose sand) to $69^{\circ}$ (dense sand), and gently curved inward to the ground surface. The widths of shear band formation above the tunnel showed a range from 1.8b to 1.9b (b=Tunnel width), which are similar to those values calculated from existing formular. The vertical height of this shear band for deep tunnel was turned out to be a bit lower than that from existing studies (3.0*Tunnel Height).