• Journal of the Korean Wood Science and Technology
• /
• v.24 no.2
• /
• pp.61-70
• /
• 1996

침엽수재(針葉樹材)(Radiata pine, Pinus radiata)MDF와 활엽수재(闊葉樹材)(Rubber wood, Hevea brasiliensis)MDF 각 1종을 대상으로 MDF를 제조하기 전 원료(原料) 섬유(纖維)의 미세(微細) 구조(構造) 및 내부결합력 시험 후 MDF의 파괴면(破壞面)에서 섬유표면(纖維表面)에 접착제(接着劑)가 도포(塗布)된 형태를 주사전자현미경(走査電子顯微鏡)으로 관찰하였다. 원료 섬유는 침(針) 활엽수재(闊葉樹材) 모두 fiber twisting 및 shrinkage fold 등이 관찰되었다. 침엽수재(針葉樹材)의 경우는 유연벽공부(有緣壁孔部)에서 유연벽공(有緣壁孔)이 없는 부분에 비하여 shrinkage fold의 발생 빈도가 낮고 표면(表面) 박리(剝離)는 가도관(假導管) 중 벽공이 없는 부분에서 관찰되었다. 활엽수재(闊葉樹材) 목섬유(木纖維)는 침엽수재(針葉樹材)와 마찬가지로 shrinkage fold가 관찰되었으나 표면(表面) 박리(剝離)는 거의 관찰되지 않았다. 활엽수(闊葉樹) 섬유(纖維)에서는 벽공의 유무에 따른 shrinkage fold의 차이(差異)가 거의 관찰되지 않았는데 이는 목섬유(木纖維)가 침엽수(針葉樹) 가도관(假導管)보다 작은 단벽공(單壁孔)을 갖기 때문으로 생각된다. 또 방사유세포(放射柔細胞)와 가도관(假導管) 및 목섬유(木纖維)의 박리(剝離) 부분(部分)에는 융기부(隆起部)가 관찰되었다. 내부결합력 시험후 나타난 파괴면을 통하여 접착제 분포를 관찰한 결과 거의 모든 섬유(纖維)들이 접착제(接着劑)로 둘러싸여 있었으며 섬유(纖維)간 접착형태(接着形態)도 매우 다양하였다. 침활엽수재(針闊葉樹材)간에 강도(强度)의 차이는 있었지만 파괴(破壞) 형태(形態)는 큰 차이를 나타내지 않았다. 즉 침활엽수(針闊葉樹) 모두 접착층(接着層)이 아닌 섬유(纖維)에서 파괴(破壞)가 발생하였으며 섬유에서 박리(剝離)된, 세포벽(細胞壁)의 일부가 다른 섬유(纖維)의 표면(表面)에 남아있는 형태와 섬유(纖維) 표면(表面)에서 떨어져 나간 형태로 관찰되었다. 세포 구성이 단순한 침엽수(針葉樹) MDF에 비하여 유세포(柔細胞)와 도관(導管) 및 목섬유(木纖維)의 파편들이 활엽수(闊葉樹) MDF에서는 다양(多樣)하게 분포하였다.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.17 no.6
• /
• pp.24-30
• /
• 2018

Dental implants are currently widely used as artificial teeth due to their good chewing performance and long life cycle. A dental implant consists of an abutment as the upper part and a fixture as the lower part. When chewing forces are repeatedly applied to a dental implant, gap at the interface surface between the abutment and the fixture is often occurred, and results in some deteriorations such as loosening of fastening screw, dental retraction and fixture fracture. To cope with such problems, a sealing-type abutment having a number of grooves along the conical-surface circumference was previously developed, and shows better sealing performance than the conventional one. This study carries out optimization of the groove shape by genetic algorithm(GA) as well as structural analysis in consideration of external chewing force and pretension between the abutment and the fixture. The overall optimization system consists of two subsystems; the one is the genetic algorithm with MATLAB, and the other is the structural analysis with ANSYS. Two subsystems transmit and receive the relevant data with each other throughout the optimization processes. The optimization result is then compared with that of the conventional one with respect to the contact pressure and the maximum stress. The result shows that the optimized model gives better sealing performance than the conventional sealing abutment.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
• /
• v.49 no.1
• /
• pp.43-48
• /
• 2023

The biocompatibility and durability of implant fixtures are major concerns for dentists and patients. Mechanical complications of the implant include abutment screw loosening, screw fracture, loss of implant prostheses, and implant fracture. This case report aims to describe management of a case of fixture damage that occurred after screw fracture in a tissue level, internal connection implant and microscopic evaluation of the fractured fixture. A trephine bur was used to remove the fixture, and the socket was grafted using allogeneic bone material. The failed implant was examined by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), which revealed a fractured fixture with both normal and irregular bone patterns. The SEM and EDS results give an enlightenment of the failed fixture surface micromorphology with microfracture and contaminated chemical compositions. Noticeably, the significantly high level of gold (Au) on the implant surface and the trace amounts of Au and titanium (Ti) in the bone tissue were recorded, which might have resulted from instability and micro-movement of the implant-abutment connection over an extended period of time. Further study with larger number of patient and different types of implants is needed for further conclusion.

• The Journal of Korean Academy of Prosthodontics
• /
• v.44 no.2
• /
• pp.229-242
• /
• 2006

Statement of problem: In order to increase preload with reducing the friction coefficient, abutment screws coated with pure gold and Teflon as dry lubricant coatings have been introduced. But the reported data indicate that if screw repeated tightening and loosening cycle, an efficiency of increasing preload was decreased by screw surface wearing off. Purpose: This study was to evaluate the influence of tungsten carbide/carbon coating, which has superior hardness and frictional wear resistance, on the preload of abutment screws and the stability of coating surface after repeated closures. Material and method: The rotational values of abutment screws and the compressive forces between abutment and fixture were measured in implant systems with three different joint connections, one external butt joint and two internal cones. Moreover the stability and the alteration of coating surface were examined by comparison of the compressive force and the removable torque values during 10 consecutive trials, observation with scanning electron microscope and analyzed the elemental composition with energy dispersive x-ray spectroscopy Results and conclusion: 1. Application of coating resulted in significant increase of compressive force in all implant systems(P<.05). The increasing rate of compressive force by coating in external butt joint was gloater than those in internal cones (P<.05). 2. Coated screw showed the significant additional rotation compared to non-coated screw in all implant systems (P<.05). There were no significant differences in the increasing rate of rotation among implant systems (P>.05). 3. Removable torque values were greater with non-coated screw than that with coated screw (P<.05). 4. Coated screw showed insignificant variations in the compressive forces during 10 consecutive trials(P>.05) 5. After repeated trials, the surface layer of coated screw was maintained relatively well. However surface wearing and irregular titanium fragments were found in non-coated screw.

• The korean journal of orthodontics
• /
• v.36 no.5
• /
• pp.324-330
• /
• 2006

Objective: The purposes of this study were to evaluate the differences between sand blasted, large grit and acid-etched (SLA) treated mini-implants and smooth surface orthodontic mini-implants in relation to the removal torque as well as the histologic analysis. Methods: Custom-made, screw-shaped, titanium implants with a length of 9.5 mm and an outer diameter of 1.8 mm were divided into 2 groups; the SLA group (20 SLA treated orthodontic mini-implants) and the smooth surface group (20 smooth surface mini-implants), and placed In the tibia metaphysis of 10 rabbits. Each rabbit had 4 mini-implants placed, 2 in each tibia. The right tibia were implanted with the SLA group mini-implants and the left tibia had the smooth group mini-implants placed. Each mini-implant group were immediately applied with a continuous traction force of 150 g using a Ni-Ti coil spring. The rabbits were sacrificed 6 weeks post-surgically. Subsequently, the legs were stabilized, the Ni-Ti coil springs were removed and the mini-implants were removed under reverse torque rotation with a digital torque gauge. Results: 6 weeks after placement, the SIA group presented a higher mean removal torque value (8.29 Ncm) than the smooth group (3.34 Ncm) and histologic analysis revealed a higher new bone formation aspect along the screw in the SLA group. Conclusion: Results of this study indicates that SLA treated mini-implants may endure higher orthodontic forces without loosening.

• Journal of Advanced Marine Engineering and Technology
• /
• v.41 no.1
• /
• pp.118-124
• /
• 2017

To investigate and analyze the cause of the failure of the connecting rod bolt and the crank pin bearing bolt of the diesel engine of this study, the following results were obtained through site surveying, the investigation of literature referring to similar failures, testing and inspection of the fracture surface, and the experience of the researchers. The fractured crank pin bearing bolt of the diesel engine is estimated to be damaged later than the connecting rod bolt. From the shape of fracture surface, it is evident that the failed connecting rod bolt is fractured by fatigue failure due to abnormally repeated loads (e.g. loosening of the connecting bolt, etc.), and is not failed by brittle fractures due to the impact load. The surface of the U-nut on the fractured connecting rod bolt has been worsening due to the improper use of lubricant (agent for prevention of thread fixing) and no usage of separating the each connecting rod on each cylinder. Moreover, there is the possibility that those poor surface conditions of the fractured connecting rod bolt have affected the failure of the connecting rod bolt of the main engine. And it could be assumed that the mechanical characteristic and manufacturing process of the failed connecting rod bolt and crank pin bearing bolt, which were made by a domestic company, conform to the design requirements for those bolts.

• Journal of Dental Rehabilitation and Applied Science
• /
• v.27 no.2
• /
• pp.185-195
• /
• 2011

In this study, titanium abutments and zirconia abutments were connected to each implant in external type implants. After that they were loaded 10000 times with 20Kg as occlusal force. The surface changes of external hexgon part and platform were observed in FESEM image. Viker's hardness of an implant, a titanium abutment and a zirconia abutment were measured respectively. 1. Viker's hardness of an implants, a titanium abutment and a zirconia abutment was $309.80{\pm}11.78$ HV, $318.40{\pm}11.82$ HV, and $1495.30{\pm}16.21$ HV respectively. There was no statistical significance between an implant and a titanium abutment (P>0.05, Anova). However, there was statistical significance between an implant and a zirconia abutment(P<0.05, Anova). 2. The wear was observed at the joint of implant and abutment in both a titanium abutment group and a zirconia abutment group after loading 10,000 times. The zirconia abutment showed more remarkable wear than the titanium one. In conclusion, the wear of external hexagon and platform was much more notable in a zirconia abutment group than a titanium one. It was suggested that it could result from the difference of surface hardness between titanium and zirconia. The wear of junction between an implant and a zirconia abutment becomes more severe, the connection of an implant and an abutment is much more unfit. This is likely to cause loosening and fracture of the abutment screw. so it is considered that the possibility of implant supra-structure failure can be increased.

• The Journal of Korean Academy of Prosthodontics
• /
• v.42 no.6
• /
• pp.628-640
• /
• 2004

Statement of problem. Wear as a result of repeated closing/opening cycles may decrease the friction coefficient of screw head, threads, and other mating components and, consequently, resistance to opening gradually decreases. It may cause screw loosening, which is one of the most common failures in implant prosthesis. Purpose. The purpose of this study is to evaluate the changes on the head and thread surface of the abutment screws after repeated closing and opening through the examination of tested screws in SEM(scanning electron microscope). Materials and methods. Five species of abutments were selected (3i-three, Avana-two) respectively by two pieces. The implant fixtures were perpendicularly mounted in liquid unsaturated polyesther(Epovia, Cray Valley Inc.) with dental surveyor. Each abutment was secured to the implant fixture by each abutment screw with recommended torque value using a digital torque controller. The abutment screws were repeatedly tightened and removed 20 times with a digital controller. FESEM (field emission scanning electron microscope, Netherland, Phillips co., model:XL 30 SFEG) was used to observe changes of each part caused by repeatedly closing/opening expeiment. First, the Photomicrographs of pre-test screws provided by each manufacturer were taken. The changes of each screw were investigated after every fifth closing and opening experiment with FESEM. Scaning electron microscope photomicrographs of each screw were taken four times. Results. As the number of closing and opening was increased, the wear or distortion of hexed or squared slot that contacted with the driver tip was more severely progressed. Wear or distortion of hexed slot was more severe than that of squared slot and it was more remarkable in the titanium screw than in the gold screw. All the tested screws showed that the width in the crest of their screw thread decreased gradually as the test was proceeded. Conclusions. Conclusively, we recommend the clinical use of gold screw, a periodic exchanges of abutment screws and avoiding repeated closing/opening unnecessarily. We also suggest a more careful manipulation of the abutment screw and screw-driver and using of abutment screw with an acute-angled slot design rather than an obtuse-angled one. Finally, it is suggested that the new slot design and the surface treatment for enduring wear or distortion should be devised.

• Clinics in Shoulder and Elbow
• /
• v.20 no.4
• /
• pp.217-221
• /
• 2017

Background: The purpose of this study was to evaluate the clinical and radiographic outcomes of internal fixation with locking T-plates for osteoporotic fractures of the proximal humerus in patients aged 65 years and older. Methods: From January 2007 through to December 2015, we recruited 47 patients aged 65 years and older with osteoporotic fractures of the proximal humerus. All fractures had been treated using open reduction and internal fixation with a locking T-plate. We classified the fractures in accordance to the Neer classification system; At the final follow-up, the indicators of clinical outcome-the range of motion of the shoulder (flexion, internal rotation, and external rotation) and the presence of postoperative complications-and the indicators of radiographic outcome-the time-to-union and the neck-shaft angle of the proximal humerus-were evaluated. The Paavolainen method was used to grade the level of radiological outcome in the patients. Results: The mean flexion was $155.0^{\circ}$ (range, $90^{\circ}-180^{\circ}$), the mean internal rotation was T8 (range, T6-L2), and the mean external rotation was $66.8^{\circ}$ (range, $30^{\circ}-80^{\circ}$). Postoperative complications, such as plate impingement, screw loosening, and varus malunion were observed in five patient. We found that all patients achieved bone union, and the mean time-to-union was 13.5 weeks of the treatment. The mean neck-shaft angle was $131.4^{\circ}$ at the 6-month follow-up. According to the Paavolainen method, "good" and "fair" radiographic results each accounted for 38 and 9 of the total patients, respectively. Conclusions: We concluded that locking T-plate fixation leads to satisfactory clinical and radiological outcomes in elderly patients with proximal humeral fractures by providing a larger surface area of contact with the fracture and a more rigid fixation.

• Journal of the Korean Geotechnical Society
• /
• v.30 no.4
• /
• pp.21-34
• /
• 2014

This paper studies the time-dependent behaviors of tunnel and surrounding ground due to tunnel deterioration. In the first part, the literature on deterioration characteristics of tunnels was reviewed. In the second part, a numerical analysis was performed to investigate the behavior of concrete lining on the typical section of Korean high-speed rail tunnel (weathered rock) after determination of input variables related to deterioration impact. The result shows that the settlement at the crown of tunnel and surface ground increased up to 7.0% and 30.2% of the total settlements during construction stage, respectively, and the internal convergence reduction of 9.0 mm for concrete linings was generated within 30 years after completion of tunnel construction. Also the loosening height increased up to 2.55 times of tunnel height within 50 years, which is higher than that of Terzaghi's recommendation on ultimate state. Due to this process of extending zones, it is found that additional loads were applied to concrete lining with the axial stress about 3.20~3.66 MPa, which accelerates tunnel deterioration. Finally the quantitative design approach to evaluate time-dependent behavior of lining and surrounding ground due to tunnel deterioration was proposed.