• Tribology and Lubricants
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• 제35권1호
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• pp.65-70
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• 2019

Self-loosening of bolts owing to external forces occurs in several machines that are clamped by bolts and nuts. This study focuses on the self-loosening of the aiming bolt of the head lamp in a vehicle. It is important to prevent the aiming bolt from self-loosening as it has a decisive effect on the angle of the head lamp. A nut clamped with a bolt, known as a retainer, is made of plastic and has a partial screw thread. In addition, a transverse load has a considerable impact on the self-loosening of a bolt. We concentrate on the self-loosening of a bolt by a transverse load. The aim of this study is to define the limits of the external force that loosen the bolt. Based on the above conditions, we derive a theoretical equation and develop a numerical analysis program that can calculate the limiting forces for self-loosening. To verify the developed program, we design a test device that can measure the self-loosening by applying sliding forces to the aiming bolt. Using this method, we can draw the following conclusions. First, the developed testing device is suitable to prove the theory for calculating the self-loosening force. Second, the equation confirms the relationship of bolt self-loosening between resistance torque and shear force. Finally, the equation obtains the minimum value of the resistance torque required to decrease the change in the angle of the head lamp, thereby improving the possibility of increasing the stability of the head lamp.

• 대한치과교정학회지
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• 제39권4호
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• pp.203-212
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• 2009

골밀도가 높고 두꺼운 피질골에 마이크로임플란트를 self-drilling 방식으로 식립하는 경우 과도한 수준의 골부하 (bone loading)가 발생할 위험이 있으며 이는 인접골의 정상적인 골개형(bone remodeling)에 장애를 초래할 수 있다. 이에, 본 연구에서는 유한요소해석으로 두께 1.0 mm의 피질골에 Absoanchor SH1312-7 마이크로임플란트((주)덴토스, 대구, 대한민국)가 self-drilling 방식으로 식립되는 과정(10회전, 식립깊이 5 mm)을 모사(simulation)하였으며 식립 단계별로 피질골에 발생되는 스트레인을 조사하였다. 식립중 마이크로임플란트 첨부의 절삭연(cutting flute)에 의한 골삭제로 생기는 나사길(threaded groove)의 치수를 얻기 위하여 가토 경골에 마이크로임플란트를 식립/제거한 후 Micro CT (Explore Locus RS, GE Healthcare, Ontario, Canada)를 이용하여 기하형상을 측정하였으며 이를 치밀골의 유한요소모델에 반영하였다. 해석결과, 치밀골에 발생되는 스트레인은 임플란트 식립깊이에 따라 증가하였고, 초기단계에서 나사산에 인접한 골에 국한되던 과부하 부위(스트레인이 4,000${\mu}$-strain을 상회하는 영역)가 식립깊이 증가에 따라 인접골 전체, 즉 나사산 인접부는 물론 골(valley) 부위에 접하는 모든 영역으로 확장되었다. 본 연구를 통해, self-drilling 방식으로 마이크로임플란트를 식립할 때 치밀골에 발생하는 스트레인 크기는 생리적인 골개형을 저해할 수 있는 수준임을 확인할 수 있었다.

• 대한치과교정학회지
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• 제41권4호
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• pp.280-287
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• 2011

Objective: This study compared the stability of cylindrical miniscrews (Cy, 7 mm in length) with that of tapered miniscrews (Ta, 5 mm in length), using torque values to determine if the healing time before loading affects the stability of the miniscrew and if the insertion torque is associated with the removal torque measured after a few weeks of healing. Methods: Ta and Cy with different thread lengths were placed in the tibias of 12 female New Zealand white rabbits (body weight: 3.0 - 3.5 kg), and the maximum insertion torque values (ITV) were measured. No orthodontic forces were applied so as to allow us to determine the pure effects of the different shapes. After 3 different healing periods (2, 4, and 6 weeks), maximum removal torque values (RTV) were measured immediately before the rabbits were sacrificed. Results: No miniscrews were loosened. There were no significant differences in ITV or RTV between the Ta and Cy nor were there any significant differences in the ITV and RTV between the 3 groups, which had different healing periods. There was a correlation between the ITV and RTV. Conclusions: Shorter Ta showed similar stability as Cy, as determined by torque values. This result strongly suggests that the tapered shape is more advantageous than the cylindrical shape. The RTV did not increase significantly over time. It is recommended that a miniscrew be loaded immediately; waiting a few weeks before loading should be avoided. The correlation between the ITV and RTV suggests that the ITV can be used to estimate a screw's future stability.

• 대한치과보철학회지
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• 제43권1호
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• pp.78-94
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• 2005

Purpose. The purpose of this study was to compare the effects of various surface treatments by measuring resonance frequency and histomorphometric analyses. Material and methods. In 5 adult dogs, the mandibular premolar were extracted. Six months later, 30 screw titanium implants (Dentium Co., Seoul, Korea) 6mm in length and 3.4mm in diameter, were placed in the mandibles of 5 dogs. Implants were divided into five groups following to surface treatment methods ; Group 1 is machined controls, Group 2 is sandblasted with large grit and acid-etched (SLA), Group 3 is anodized (Autoelectric Co., Korea, 660Hz, Duty10), Group 4 is hydroxyapatite(HA) coated by ion beam assisted deposition(E-beam), Group 5 is hydroxyapatite(HA) coated with Sol-gel coating process. Resonance frequency was measured implant placement immediately, and 3, 6 weeks and 10 weeks of healing perods. With the animal subject's sacrifice 10 weeks after implantation, implants were removed on bloc and histologic and computer-based histomorphometric analyses were performed. Histomorphometric analysis involved quantification of the entire bone to metal contact around the implants. Statistical analyses were performed using the SPSS for Windows (ver. 9.0 SPSS Inc.) Statistical differences were considered significant at P<0.05. Results. The results were as follows : 1) In five groups, mean value of resonance frequency analysis(RFA) were highest in group 5 (Sol-gel implant) at implantation and those of group 4 (E-beam)was highest at 10 weeks . but there was no correlation between surface treatments and RFA. 2) In all surface treatment groups, the RFA values of implants decreased until 3 weeks and increased to 10 weeks. 3) The percentage of direct bone-to-implant contact (BIC) had statistical significance between five groups in cancellous bone, (P<0.05) the percentage of bone density inside the thread had no statistical significance between five groups. (P>0.05) 4) There was a significant difference between cortical bone and cancellous bone in BIC. (P<0.05) and bone density. (P<0.05) 5) There was a correlation between the RFA value of implants at 10 weeks and BIC in cancellous bone, and between the RFA value of implants at 10 weeks and bone density in cortical bone. (P<0.05). Conclusions. These results indicate that surface treatment does not affect the implant stability in case of good bone quality.