• The Journal of Korean Academy of Prosthodontics
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• v.45 no.3
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• pp.329-338
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• 2007

Purpose. The aim of this study is to evaluate the effect of TiN coating of abutment screw on the unscrewing torque. Material and methods. Titanium and Gold-Tite abutment screws were classified into two groups, Group A and C respectively, as control groups. Titanium abutment screws with TiN coatings were also classified into two groups, Group B and D, as experimental ones. Group A and B were tightened to 20 Ncm input torque, and Group C and D were tightened to 32 Ncm torque. Detorque values were measured with digital torque gauge during repeated closing and opening experiment. Results. Abutment screws with TiN coating (Group B and D) showed statistically significant higher mean detorque values than those of Group A and C. Discussion. Physical properties of TiN coating, such as low friction coefficient, high hardness and wear resistance, might contribute to higher detorque values. Conclusion. It is suggested that TiN coating of abutment screw help to reduce the risk of screw loosening and improve the stability of screw joint.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.526-529
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• 2005

The purpose of this study is to investigate a loosening process of screws through a fatigue test. Therefore, it is attempted to perform an interbody fusion on porsine lumbar spine using cage and screws. From the results, it is found that the combining force in both of the cylinder and the taper type screws located on the upper-left first start to decrease and then the combination between a rod and screw loosens. In addition, it is investigated that the life of taper type screw increases 5.5% and this fact is coincident with the previous results.

• Laser Solutions
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• v.14 no.4
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• pp.1-8
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• 2011

This study is about laser welded joints in order to replace the traditional screw connection of a differential gear and its case in the differential gear assembly. Screws are usually used to join these parts. But the screws take up weight and space. So we needed to improve the joining method. In the welding of a differential gear and its case, the quality is much harder to control, because the high carbon contents of the two components results in cold cracks. But a new method that adds wire allows these materials to be joined. Additionally, more distortions generally occurs in the welded joints than in screws. We tried to prove that laser welding is an available method for joining these parts through the measurement and various tests.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.46 no.6
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• pp.393-402
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• 2020

Objectives: Here, we present cases of mandibular fracture that were managed with the cortical lag screw fixation technique (CLSFT) in order to critically evaluate technique indications and limitations of application at various fracture sites. Materials and Methods: This was a retrospective cohort study. The study sample was composed of patients suffering from mandibular fractures that were treated by the CLSFT. The outcome variables were fracture type, duration of surgery, number of screws, and pattern of application. Other study categories included patient demographics and causes of injury. Chi-square tests were used to assess descriptive and inferential statistical differences, and the P-value was set at 0.05. Results: Thirty-three patients were included in the study sample, with a mean age of 30.9±11.5 years and a male predominance of 81.8%. The technique was applied more frequently in the anterior mandibular region (51.5%) than in other sites. Double CLSFT screws were required at the symphysis and parasymphysis, while single screws were used for body and angle regions. No intraoperative and postoperative variables were significantly different except for surgical duration, which was significantly different between the sites studied (P=0.035). Conclusion: We found that CLSFT is a rapid, cost-effective technique for the fixation of mandibular fractures yielding good treatment results and very limited complications. However, this technique is sensitive and requires surgical expertise to be applied to mandibular fractures that have specialized characteristics.

• Journal of Biomedical Engineering Research
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• v.42 no.1
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• pp.1-6
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• 2021

Recently, various types of pedicle screws have been developed considering the anatomical structure of the spine. The purpose of this study was to evaluate the pullout stiffness and strength of two types of commercial pedicle screws. The design of two type screws were single pitched thread (ST) pedicle screw and dual pitched thread (DT) pedicle screw, respectively. The tests were conducted in accordance with the ASTM standards using polyurethane (PU) test blocks which has anatomical structure of the spine. There was no significant difference in pullout stiffness between two types of screw. However, DT exhibited higher pullout strength than ST (p<0.05). Pedicle screw with dual pitched thread showed higher pullout strength without decrease in pullout stiffness compared to the standard pedicle screw. In conclusion, dual pitched thread design of the pedicle screw is considered to be more suitable than the single pitched thread for the anatomical structure of the spine.

• Journal of Veterinary Science
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• v.23 no.2
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• pp.38.1-38.13
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• 2022

Background: Minimally invasive surgery (MIS) technique of sacroiliac luxation in toy breed dogs using cannulated screws has not been described. Objectives: The purpose of this study was to evaluate the effectiveness of pelvic canal recovery, the reproducibility of successful surgery outcomes, and the acceptable difficulty of the procedure in MIS of sacroiliac luxation in toy breed dogs. Methods: MIS using 2.3-mm cannulated screws was demonstrated in 12 toy breed dog cadavers with sacroiliac luxation artificially induced. Pre and postoperative radiographs were used to evaluate the pelvic canal diameter ratio (PCDR), hemipelvic canal width ratio (HCWR), and reduction rate. Dorsoventral angle (DVA) and craniocaudal angle (CCA) of the inserted screw were obtained postoperative computed tomographic scan. Results: The statistically significant difference between the mean pre and postoperative PCDR was found (1.10 ± 0.12 and 1.26 ± 0.11, respectively; p = 0.002), and the mean HCWR close to 1.0 meaning symmetric pelvis also was obtained (0.97 ± 0.07). The mean DVA and CCA were 2.26° ± 1.33° and 2.60° ± 1.86°, respectively. Conclusions: MIS of sacroiliac luxation using 2.3-mm cannulated screws is applicable to toy breed dogs with acceptable difficulty.

• The korean journal of orthodontics
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• v.37 no.1 s.120
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• pp.5-15
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• 2007

Objective: The purpose of this study was to evaluate the mechanical performance of mini-screws during insertion into artificial bone with use of the driving torque tester (Biomaterials Korea, Seoul, Korea), as well as testing of Pull-out Strength (POS). Methods: Experimental bone blocks with different cortical bone thickness were used as specimens. Three modules of commercially available drill-free type mini-screws (Type A; pure cylindrical type, Biomaterials Korea, Seoul, Korea, Type B; partially cylindrical type, Jeil Medical, Seoul, Korea, Type C; combination type of cylindrical and tapered portions, Ortholution, Seoul, Korea), were used. Results: Difference in the cortical bone thickness had little effect on the maximum insertion torque (MIT) in Type A mini-screws. But in Type B and C, MIT increased as the cortical bone thickness Increased. MIT of Type C was highest in all situations, then Type B and Type A in order. Type C showed lower POS than Type A or B in all situations. There were statistically significant correlations between cortical bone thickness and MIT, and POS for each type of the mini-screws. Conclusion: Since different screw designs showed different insertion torques with increases in cortical bone thickness, the best suitable screw design should be selected according to the different cortical thicknesses at the implant sites.

• Journal of Biomedical Engineering Research
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• v.38 no.1
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• pp.9-15
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• 2017

Recently, flexible cages have been introduced in an attempt to absorb and reduce the abnormal load transfer along the anterior parts of the spine. They are designed to be used with the pedicle screw systems to allow some mobility at the index level while containing ROM at the adjacent level. In this study, a finite element (FE) study was performed to assess biomechanical efficacies of the flexible cage when combined with pedicle screws with flexible rods. The post-operated models were constructed by modifying the L4-5 of a previously-validated 3-D FE model of the intact lumbar spine (L2-S1): (1) Type 1, flexible cage only; (2) Type 2, pedicle screws with flexible rods; (3) Type 3, interbody fusion cage plus pedicle screws with rigid rods; (4) Type 4, interbody fusion cage plus Type 2; (5) Type 5, Type 1 plus Type 2. Flexion/extension of 10 Nm with a compressive follower load of 400N was applied. As compared to the Type 3 (62~65%) and Type 4 (59~62%), Type 5 (53~55%) was able to limit the motion at the operated level effectively, despite moderate reduction at the adjacent level. It was also able to shift the load back to the anterior portions of the spine thus relieving excessively high posterior load transfer and to reduce stress on the endplate by absorbing the load with its flexible shape design features. The likelihood of component failure of flexble cage remained less than 30% regardless of loading conditions when combined with pedicle screws with flexible rods. Our study demonstrated that flexible cages when combined with posterior dynamic system may help reduce subsidence of cage and degeneration process at the adjacent levels while effectively providing stability at the operated level.

• The korean journal of orthodontics
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• v.38 no.1
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• pp.5-12
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• 2008

Objective: This study was designed to analyze the primary and secondary stability characteristics of orthodontic mini-screws of tapered design when compared with the cylinder mini-screw. Methods: A total of 48 mini-screws were placed into the buccal alveolar bone of the mandible in 6 male beagle dogs. Comparison was made between tapered and cylinder type mini-screws (Biomaterials Korea, Seoul, Korea). Maximum insertion torque (MIT) was measured using a torque sensor (Mark-10, MGT 50, USA) during installation, and maximum removal torque (MRT) was recorded after 3 and 12 weeks of loading. Results: Taper mini-screws showed a higher MIT value of 22.3 Ncm compared with cylinder mini-screw showing 13.6 Ncm (p < 0.001). The MRT of the taper mini-screw showed a significantly higher value of 9.1 Ncm than those of cylinder mini-screw of 5.7 Ncm at 3-weeks after installation (p < 0.05). However, there was no difference in the MRT value between the taper and cylinder mini-screws at 12 weeks of loading. Conclusions: These results showed that the high insertion torque of the taper mini-screw design increases initial stability until 3 weeks of loading, but does not have any effect on the secondary stability at 12 weeks of loading.

• Journal of the Korean Society for Precision Engineering
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• v.34 no.3
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• pp.173-178
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• 2017

Recently, a high-precision ball screw is an essential part of high-speed machines. However, producing high-precision ball screws has been costly and time-consuming. Nowadays, a whirling machine is used to produce high-precision ball screws efficiently. Rotating multi-tips are used to turn the ball screw in the whirling machine. In this study, a structural analysis was performed by a finite-element method to develop a whirling machine. An improved model of the whirling machine was proposed by the analysis. In addition, a thermal analysis was performed to confirm the thermal stability. The results of the analysis can be applied in order to further develop the whirling machine.