• Journal of Periodontal and Implant Science
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• 제46권3호
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• pp.152-165
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• 2016

Purpose: This study investigated the effects of bone density and crestal cortical bone thickness at the implant-placement site on micromotion (relative displacement between the implant and bone) and the peri-implant bone strain distribution under immediate-loading conditions. Methods: A three-dimensional finite element model of the posterior mandible with an implant was constructed. Various bone parameters were simulated, including low or high cancellous bone density, low or high crestal cortical bone density, and crestal cortical bone thicknesses ranging from 0.5 to 2.5 mm. Delayed- and immediate-loading conditions were simulated. A buccolingual oblique load of 200 N was applied to the top of the abutment. Results: The maximum extent of micromotion was approximately $100{\mu}m$ in the low-density cancellous bone models, whereas it was under $30{\mu}m$ in the high-density cancellous bone models. Crestal cortical bone thickness significantly affected the maximum micromotion in the low-density cancellous bone models. The minimum principal strain in the peri-implant cortical bone was affected by the density of the crestal cortical bone and cancellous bone to the same degree for both delayed and immediate loading. In the low-density cancellous bone models under immediate loading, the minimum principal strain in the peri-implant cortical bone decreased with an increase in crestal cortical bone thickness. Conclusions: Cancellous bone density may be a critical factor for avoiding excessive micromotion in immediately loaded implants. Crestal cortical bone thickness significantly affected the maximum extent of micromotion and peri-implant bone strain in simulations of low-density cancellous bone under immediate loading.

• The Journal of Advanced Prosthodontics
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• 제4권4호
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• pp.227-234
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• 2012

PURPOSE. The aims of this pilot study were to introduce implant loading devices designed for animal study and to evaluate the validity of the load transmission ability of the loading devices. MATERIALS AND METHODS. Implant loading devices were specially designed and fabricated with two implant abutments and cast metal bars, and orthodontic expansion screw. In six Beagles, all premolars were extracted and two implants were placed in each side of the mandibles. The loading device was inserted two weeks after the implant placement. According to the loading protocol, the load was applied to the implants with different time and method, simulating early, progressive, and delayed loading. The implants were clinically evaluated and the loading devices were removed and replaced to the master cast, followed by stress-strain analysis. Descriptive statistics of remained strain (${\mu}{\varepsilon}$) was evaluated after repeating three cycles of the loading device activation. Statistic analysis was performed using nonparametric, independent t-test with 5% significance level and Friedman's test was also used for verification. RESULTS. The loading devices were in good action. However, four implants in three Beagles showed loss of osseointegration. In stress-strain analysis, loading devices showed similar amount of increase in the remained strain after applying 1-unit load for three times. CONCLUSION. Specialized design of the implant loading device was introduced. The loading device applied similar amount of loads near the implant after each 1-unit loading. However, the direction of the loads was not parallel to the long axis of the implants as predicted before the study.

• The Journal of Advanced Prosthodontics
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• 제10권2호
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• pp.85-92
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• 2018

PURPOSE. This research evaluated clinical outcomes of two types of hydroxyapatite (HA)-coated implants: OT (Osstem TS III-HA, Osstem implant Co., Busan, Korea) and ZM (Zimmer TSV-HA, Zimmer dental, Carlsbad, USA). MATERIALS AND METHODS. The research was conducted on 303 implants (89 of OT, 214 of ZM), which were placed from January 16, 2010 to December 20, 2012. The prognosis was evaluated in terms of success rates, survival rates, annual marginal bone loss, and implant stability quotients (ISQ). The samples were classified into immediate, early, conventional, and delayed groups according to the loading time. RESULTS. Overall, there were no significant differences between OT and ZM in success rates, survival rates, and annual marginal bone loss, except for the result of secondary stability. OT showed $77.83{\pm}8.23ISQ$, which was marginally higher than $76.09{\pm}6.90ISQ$ of ZM (P<.05). In terms of healing periods, only immediate loading showed statistically significant differences (P<.05). Differences between OT and ZM were observed in terms of two indices, the annual marginal bone loss ($0.17{\pm}0.58mm/year$ < $0.45{\pm}0.80mm/year$) and secondary stability ($84.36{\pm}3.80ISQ$ > $82.48{\pm}3.69ISQ$) (P<.05). OT and ZM did not have any statistically significant differences in early, conventional, and delayed loading (P>.05). CONCLUSION. OT (97.75%) and ZM (98.50%) showed relatively good outcomes in terms of survival rates. In general, OT and ZM did not show statistically significant differences in most indices (P>.05), although OT performed marginally better than ZM in the immediate loading and 1-stage surgery (P<.05).

• 대한금속재료학회지
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• 제50권1호
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• pp.52-58
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• 2012

Hydrogen-delayed fracture (HDF) was analyzed from the deposited weld metals of 600-MPa and 800-MPa flux-cored arc (FCA) welding wires, and then from the diffusible hydrogen behavior of the weld zone. Two types of deposited weld metal, that is, rutile weld metal and alkali weld metal, were used for each strength level. Constant loading test (CLT) and thermal desorption spectrometry (TDS) analysis were conducted on the hydrogen pre-charged specimens electrochemically for 72 h. The effects of microstructures such as acicular ferrite, grain-boundary ferrite, and low-temperature-transformation phase on the time-to-failure and amount of diffusible hydrogen were analyzed. The fracture time for hydrogen-purged specimens in the constant loading tests decreased as the grain size of acicular ferrite decreased. The major trapping site for diffusible hydrogen was the grain boundary, as determined by calculating the activation energies for hydrogen detrapping. As the strength was increased and alkali weld metal was used, the resistance to HDF decreased.

• 한국임상수의학회지
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• 제20권2호
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• pp.207-211
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• 2003

This investigation aimed to determine the relative merit of osseointegration in immediate and delayed implantation in the dog mandible using radiography and bone scintigraphy. five adult mongrel dogs with a mean weight of 8.5 kg were used in this investigation. During the entire study period. all dogs were fed with a soft commercial diet and water ad libitum to minimize functional loading of the implant. Twenty titanium alloy systems 4 mm in diameter and 10 mm in length blasted with calcium phosphate were prepared for insertion. The second and third left mandibular premolars in each dog were extracted for the delayed implant insertion. Twelve weeks later, the second and third right mandibular premolars were extracted for the immediate implant insertion. Before the delayed and immediate implantation procedures and 0, 4, 8, and 12 weeks after the insertions, radiography and bone scintigraphy were conducted. Bone scans were obtained using a large field of view gamma camera equipped with a collimator about 3 hours after intravenous injection of Tc-99m-MDP to the dogs. All the dogs were evaluated weekly for inflammation, necrosis, and other of the bone or sort tissue. Significant macroscopic lesions were not detected. Radioisotope scintigraphy with Tc-99m-MDP hat proved to be a reliable method for measuring increased bone activity at specific skeleton tissue sites. In conclusion, osseointegration in peri-implant bone did not differ significantly between the immediate and delayed implant procedures during the experimental period. The immediate implant may be an alternative treatment of implant insertion in animals.

• 대한수의학회지
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• 제44권1호
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• pp.131-136
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• 2004

Osseointegration involves anchoring dental implants to stable bone rather than to soft-tissue. Clinical osseointegration is currently defined as the process whereby alloplastic material is asymptomatically and rigidly fixed and maintained in bone during functional loading. Full osseointegration is necessary for the success of long-term dental implants. Recent developments in computer assisted measurement of bone formation have improved maxillofacial examination and osseointegration. Computer assisted examination has also proved effective in dental implantology. This investigation was aimed to determine osseointegration in immediate and delayed implantation in the dog mandible using dental computed tomography (CT) and bone scintigraphy. Five adult (mean age of 2 years) mongrel dogs with a mean weight of 9.1 kg were used in this investigation. Titanium alloy implant systems with 4 mm in diameter and 10 mm in length were chosen for insertion. The second and third left mandibular premolars in each dog were extracted for the delayed implant insertion. Twelve weeks later, the second and third right mandibular premolars were extracted for the immediate implant insertion. Before the delayed and immediate implantation procedures and 0, 4, 8, and 12 weeks after the insertions, dental CT and scintigraphy were conducted. The CT and scintigraphic images indicate that reconstruction of bone surrounding of the immediate implant can be as successful as reconstruction of bone surrounding of the delayed implant.

• Computers and Concrete
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• 제19권1호
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• pp.59-68
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• 2017

This study focused on modeling the behavior of the compressive stress using the average strain and ultrasonic test results in concrete. Feed-forward backpropagation artificial neural network (ANN) models were used to compare four types of concrete mixtures with varying water cement ratio (WC), ordinary concrete (ORC) and concrete with short steel fiber-reinforcement (FRC). Sixteen (16) $150mm{\times}150mm{\times}150mm$ concrete cubes were used; each contained eighteen (18) data sets. Ultrasonic test with pitch-catch configuration was conducted at each loading state to record linear and nonlinear test response with multiple step loads. Statistical Spearman's rank correlation was used to reduce the input parameters. Different types of concrete produced similar top five input parameters that had high correlation to compressive stress: average strain (${\varepsilon}$), fundamental harmonic amplitude (A1), $2^{nd}$ harmonic amplitude (A2), $3^{rd}$ harmonic amplitude (A3), and peak to peak amplitude (PPA). Twenty-eight ANN models were trained, validated and tested. A model was chosen for each WC with the highest Pearson correlation coefficient (R) in testing, and the soundness of the behavior for the input parameters in relation to the compressive stress. The ANN model showed increasing WC produced delayed response to stress at initial stages, abruptly responding after 40%. This was due to the presence of more voids for high water cement ratio that activated Contact Acoustic Nonlinearity (CAN) at the latter stage of the loading path. FRC showed slow response to stress than ORC, indicating the resistance of short steel fiber that delayed stress increase against the loading path.

• Earthquakes and Structures
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• 제21권5호
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• pp.445-460
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• 2021

This study experimentally explored the behaviour of 12 concrete filled steel tube (CFST) and steel tube columns subjected to lateral cyclic loading. The L/D ratio was 12.3 while D/t ratios were 45.4, 37.8 and 32.4, classifying these 12 specimens into 3 groups. Each group included 3 CFST and 1 steel tube columns and were tested to failure. The experimental results indicated that CFST specimens reached the state of 'collapse prevention' (drift 4%) prior to the occurrence of local buckling. Strength degradation of CFST specimens did not occur up to the failure by buckling. This showed the favourable characteristic of CFST columns in preventing collapse of structures subjected to earthquakes. The high energy absorption capability in the post collapse limit state was appropriate for dissipating energy in structures. Compared to steel tube columns, CFST columns delayed local buckling and prevented inward buckling. Consequently, CFST columns exhibited their outstanding seismic performance in terms of the increased ultimate resistance, capacity to sustain 2-3 additional load cycles and significantly higher drift. A simple and reasonably accurate model was proposed to predict the ultimate strength of CFST columns under lateral cyclic loading.

• Nuclear Engineering and Technology
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• 제41권2호
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• pp.171-178
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• 2009

The rate of delayed hydride cracking (DHC), V, has been measured in cold-worked and stress-relieved Zircaloy-4 fuel cladding using the Pin-Loading Tension technique. At $250^{\circ}C$ the mean value of V from 69 specimens was $3.3({\pm}0.8)x10^{-8}$ m/s while the temperature dependence up to $275^{\circ}C$ was described by Aexp(-Q/RT), where Q is 48.3 kJ/mol. No cracking or cracking at very low rates was observed at higher temperatures. The fracture surface consisted of flat fracture with no striations. The results are compared with previous results on fuel cladding and pressure tubes.

• Nuclear Engineering and Technology
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• 제35권4호
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• pp.336-346
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• 2003

This study is intended to evaluate the dependency of TRU recycling characteristics on the neutron spectrum shift in a Pb-Bi cooled core. Considering two Pb-Bi cooled cores with the soft and the hard spectrum, respectively, various characteristics of the recycled core are carefully examined and compared with each other. Assuming very simplified fuel cycle management with the homogeneous and single region fuel loading, the burnup calculations are performed until the recycled core reached to the (quasi-) equilibrium state. The mechanism of TRU recycling toward the equilibrium is analyzed in terms of burnup reactivity and the isotopic compositions of TRU fuel. In the comparative analyses, the difference in the recycling behavior between the two cores is clarified. In addition, the basic safety characteristics of the recycled core are also discussed in terms of the Doppler coefficient, the coolant loss reactivity coefficient, and the effective delayed neutron fraction.