• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.34 no.3
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• pp.325-340
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• 2008

The purpose of this study was to evaluate the artificial dental plaque by Streptococcus mutans on 4 different implant surfaces. In this study, the specimens were divided into 4 groups according to implant surface treatment. Uncoated implant group(n=5) which has an uncoated, smooth surfaced implant(Osstem, Korea), SLA implant group(n=5) which has an sandblasted large grit and acid-etched surface implant(Bicon, USA). Oxidized implant group(n=5) which has an oxidized surfaced implant (Osstem, Korea), and RBM implant group(n=5) which has resorbable blasting media(RBM) surfaced implant(Osstem, Korea). Acquired pellicle by human saliva and dental plaque by Streptococcus mutans were made on each implant surface. To analyze the plaque condition on implants surfaces, cell count and optical density were taken as a microbiologic method, and SEM(Scanning Electronic Microscope) findings was also taken for evaluation of surface condition. The following results were obtained. 1. Cell counting results of artificial dental plaque were Uncoated group($658.0{\pm}102.0$), RBM group($878.0{\pm}170.0$), SLA group ($946.0{\pm}42.0$), Oxidized group($992.0{\pm}40.0$), and there was difference between Oxidized group and Uncoated implant group(p<0.05). In case of modified cell counting results by v/w% were RBM group($197.8{\pm}45.2$), Oxidized group($207.04{\pm}8.34$), Uncoated group($261.6{\pm}40.6$), SLA group($315.4{\pm}14.0$), and there was difference between RBM group and SLA group(p<0.05). 2. Optical density results of artificial dental plaque after ultrasonic treatment was that there was difference among groups, and optical density of RBM group was higher than that of Uncoated group(p<0.05). In case of modified optical density results by v/w%, there was difference among groups, and the modified optical density of Uncoated group and SLA group was higher than those of Oxidized group and RBM group(P>0.05). 3. SEM findings of artificial dental plaque on the surfaces of implant as follows; there were artificial dental plaque on the surfaces of all test implants. Streptococcus mutans and by-product were observed at 10,000 times magnified condition on all test implants. Adhesion area of artificial dental plaque was about 1/2 of total surface after 24 hours incubate at $37^{\circ}C$. These results showed that there were differences among implant surfaces on the growth of Streptococcus mutans, and bacteria and by-product were covered about 1/2 area of total implant surfaces at 24 hours incubate at $37^{\circ}C$.

• The Journal of Advanced Prosthodontics
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• v.11 no.1
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• pp.7-15
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• 2019

PURPOSE. The aim of this study was to identify the effects of three aesthetic restorative materials on the wear between tooth and restoration by a pin-on-disk manner. MATERIALS AND METHODS. Six aesthetic restorative materials were used to prepare disk specimens for wear test, which were Lava Zirconia as zirconia group, Vintage MP and Cerabien ZR as veneering porcelain group, Gradia Direct microhybrid composite containing prepolymerized fillers, Filtek Z250 microhybrid composite containing zirconia glass and colloidal silica particles, and Filtek Z350 nanocomposite as composite resin group. Vertical loss of the worn cusp, change of the surface roughness of the restoration materials, and the surface topography were investigated after wear test under 9.8-N contact load. RESULTS. The porcelain groups (Vintage MP and Cerabien ZR) caused the largest vertical loss of teeth when compared with those of the composite resin and zirconia groups, and Filtek Z250 microhybrid composite results in the second-largest vertical loss of teeth. The surface of Filtek Z350 nanocomposite was deeply worn out, but visible wear on the surface of the zirconia and Gradia Direct microhybrid composite was not observed. When the zirconia surface was roughened by sand-blasting, vertical loss of teeth considerably increased when compared with that in the case of fine polished zirconia. CONCLUSION. It was identified that microhybrid composite resin containing a prepolymerized filler and zirconia with reduced surface roughness by polishing were the most desirable restorative materials among the tested materials to prevent the two-body wear between aesthetic restorative material and tooth.

• Journal of the Korean Geotechnical Society
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• v.25 no.10
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• pp.17-30
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• 2009

Underground construction such as tunneling can induce damages on the surrounding rock mass, due to the stress concentration of in situ stresses and excessive energy input during construction sequence, such as blasting. The developed damage on the rock mass can have substantial influence on the mechanical and hydraulic behaviors of the rock masses around a tunnel. In this study, investigation on the generation of damage around an opening in a jointed rock model under biaxial compression condition was conducted. The joint dip angles employed are 30, 45, and 60 degrees to the horizontal, and the synthetic rock mass was made using early strength cement and water. From the biaxial compression test, initiation and propagation of tensile cracks at norm to the joint angle were found. The propagated tensile cracks eventually developed rock blocks, which were dislodged from the rock mass. Furthermore, the propagation process of the tensile cracks varies with joint angle: lower joint angle model shows more stable and progressive tensile crack propagation. The development of the tensile crack can be explained under the hypothesis that the rock segment encompassed by the joint set is subjected to the developing moment, which can be induced by the geometric irregularity around the opening in the rock model. The experiment results were simulated by using discrete element method PFC 2D. From the simulation, as has been observed from the test, a rock mass with lower joint angle produces wider damage region and rock block by tensile cracks. In addition, a rock model with lower joint angle shows progressive tensile cracks generation around the opening from the investigation of the interacted tensile cracks.

• The Journal of Korean Academy of Prosthodontics
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• v.51 no.3
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• pp.167-174
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• 2013

Purpose: This study was conducted to evaluate the roughness and surface alternations of three differently blasted titanium discs treated by $Nd:YVO_4$ Laser irradiation in different conditions. Materials and methods: Thirty commercially pure titanium discs were prepared and divided into three groups. Each group was consisted of 10 samples and blasted by $ZrO_2$ (zirconium dioxide), $Al_2O_3$ (aluminum oxide), and RBM (resorbable blasted media). All the samples were degreased by ultrasonic cleaner afterward. Nine different conditions were established by changing scanning speed (100, 300, 500 mm/s) and repetition rate (5, 15, 35 kHz) of $Nd:YVO_4$ Laser (Laser Pro D-20, Laserval $Korea^{(R)}$, Seoul, South Korea). After laser irradiation, a scanning electron microscope, X-ray diffraction analysis, energy dispersive X-ray spectroscopic analysis, and surface roughness analysis were used to assess the roughness and surface alternations of the samples. Results: According to a scanning electron microscope (SEM), titanium discs treated with laser irradiation showed characteristic patterns in contrast to the control which showed irregular patterns. According to the X-ray diffraction analysis, only $Al_2O_3$ group showed its own peak. The oxidation tendency and surface roughness of titanium were similar to the control in the energy dispersive X-ray spectroscopic analysis. The surface roughness was inversely proportional to the scanning speed, whereas proportional to the repetition rate of $Nd:YVO_4$. Conclusion: The surface microstructures and roughness of the test discs were modified by the radiation of $Nd:YVO_4$ laser. Therefore, laser irradiation could be considered one of the methods to modify implant surfaces for the enhancement of osseointegration.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.33 no.4
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• pp.348-355
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• 2000

This paper described the relationship between the behavior of the Israeli carp, Cyprinus carpio and the environmental noise level due to the dynamite explosion work. The experiment was conducted in the cage ($L10{\times}W4{\times}D4 m$) of aquaculture located at Chungjoo Lake, Chechon, in 1997. The fish trajectory was obtained by the telemetry system in which a pulsed ultrasonic pinger ($50 kHz, {\phi}16{\times}L70 mm$) attached to the fish was tracked three dimensionally, and the underwater noise levels were measured. The results of the study were as follows: 1. The underwater noise levels in the normal blasting measured at a distance of 400 m from the source of noise increased by $40 dB (re 1 {\mu}Pa)$ compared to the levels before explosion. The dominant frequency and the increased power spectrum level of the underwater noise by the explosion work were $75 to 100 Hz and 22.9 to 35.3 dB$, respectively. 2. The underwater noise levels in the test blasting measured at a distance of 350 m from the source of noise increased by average $49.5 dB (re 1 {\mu}Pa)$compared to the levels before explosion. 3. The swimming area of the fish was reduced with the time after explosion, and after more than one hour the fish represented the similar swimming area and behavior to the status of right before explosion. 4, The swimming depth layer of the fish was most of the case at the sea surface less than 1,0 m except during explosion or right after of it. But the fish swam downward when an external stimulus like the explosion noise was given to the fish. 5. The average swimming speeds of the fish before, during and after the works were about 1.2 times, 1.9 times and 1.0 times of the body length, respectively, and the speed of the fish with explosion was faster 1.6 times than the speed without of that. Consequently, the explosion noise levels measured by this study were sufficiently high to affect the fish, and the heavy shock by the explosion works could produce a considerable unfavorable effects to the fish.

• Tunnel and Underground Space
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• v.16 no.1 s.60
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• pp.50-57
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• 2006

Development of structures such as slope and tunnel, waste disposal, oil and LPG storages, and underground power house and so on, is increasing with the year. The method for appropriate estimation of rock state such as fresh or damaged rocks is also requested with increasing structural development. On these purposes, seismic logging system, which is a simple and easy way for handling as well as small and light, has been developed. Seismic logging method is one of logging tests, which is able to evaluate the state of rock mass with various shapes and is possible to obtain the relatively accuracy data at situ state. In addition, seismic logging method is at to apply to estimate structural behavior, before and after support installed. According to the results obtained from this study, firstly, it is clear that the extent of damage in rock slope due to blasting is able to be evaluated with quantity using seismic logging method, moreover to decide the damage zone in rock slope reasonably. Secondly, it is expected that installing depth of support is able to be decided more effectively and economically, using the results of seismic logging data. Finally, seismic logging method is also able to be applied safety supervision of structures, before and after support installed.

• The Journal of Advanced Prosthodontics
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• v.7 no.1
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• pp.1-7
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• 2015

PURPOSE. This study was performed to evaluate shear bond strength (SBS) between three dual-cured resin cements and silica coated zirconia, before and after thermocycling treatment. MATERIALS AND METHODS. Sixty specimens were cut in $15{\times}2.75mm$ discs using zirconia. After air blasting of $50{\mu}m$ alumina, samples were prepared by tribochemical silica coating with $Rocatec^{TM}$ plus. The specimens were divided into three groups according to the dual-cure resin cement used: (1) Calibra silane+$Calibra^{(R)}$, (2) Monobond S+$Multilink^{(R)}$ N and (3) ESPN sil+$RelyX^{TM}$ Unicem Clicker. After the resin cement was bonded to the zirconia using a Teflon mold, photopolymerization was carried out. Only 10 specimens in each group were thermocycled 6,000 times. Depending on thermocycling treatment, each group was divided into two subgroups (n=10) and SBS was measured by applying force at the speed of 1 mm/min using a universal testing machine. To find out the differences in SBS according to the types of cements and thermocycling using the SPSS, two-way ANOVA was conducted and post-hoc analysis was performed by Turkey's test. RESULTS. In non-thermal aged groups, SBS of Multilink group (M1) was higher than that of Calibra (C1) and Unicem (U1) group (P<.05). Moreover, even after thermocycling treatment, SBS of Multilink group (M2) was higher than the other groups (C2 and U2). All three cements showed lower SBS after the thermocycling than before the treatments. But Multilink and Unicem had a significant difference (P<.05). CONCLUSION. In this experiment, Multilink showed the highest SBS before and after thermocycling. Also, bond strengths of all three cements decreased after thermocycling.

• Journal of Technologic Dentistry
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• v.33 no.4
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• pp.349-357
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• 2011

Purpose: In this study, for the reasons of observing the changes when using bonding agent with Ni-Cr alloy and Co-Cr alloy and using VM13 and Vintage MP ceramic which have the disparity in coefficient of thermal expansion, it is carried out to evaluate the characteristics of the bonding agent through the analysis of the interface between metal and ceramic and the analysis of bond strength by variable. Methods: The surface treatment was performed on the two kinds of alloy(Ni-Cr alloy and Co-Cr alloy) specimens, which were sandblasted and were treated with bonder application. The metal-ceramic interfaces were analyzed with EPMA in order to ionic diffusion, and the shear test was performed. Results: As a result of observation of metal-ceramic interfacial properties, it was observed that Cr atoms were spread from the alloy body to the ceramic floor in the specimen of Group B. It was also seen that Cr, W atoms were spread from the alloy body to the ceramic floor in the specimen of Group S. In consequence of observing Shear bond strength, it was calculated that the specimen of BSV was 27.75(${\pm}11.21$)MPa, BSM was 27.02(${\pm}5.23$)MPa, BCV was 30.20(${\pm}5.99$)MPa, BCM was 27.94(${\pm}10.76$)MPa, SSV was 20.83(${\pm}2.58$)MPa, SSM was 23.98(${\pm}3.94$)MPa, SCV was 32.32(${\pm}4.68$)MPa, and SCM was 34.54(${\pm}10.63$)MPa. Conclusion: In the metal-ceramic interface of Bellabond plus sample group, diffusion of Cr atoms was incurred and diffusion of C Cr atoms and W atoms in the sample group of $Starloy{(R)}\;C$ was observed. Using bonding agent showed the higher bond strength than using the sand blasting treatment. In the Bellabond plus alloys, the specimen group with the use of binding materials showed higher shear bond strength, but didn't show statistically significant differences (p>0.05). In the $Starloy{(R)}\;C$ alloys, the specimen group with the use of binding materials showed higher shear bond strength and statistically significant differences(p<0.05). In terms of VM13 ceramic, it was in the Bellabond plus alloys that the high shear bond strength was showed, but there's no statistically significant differences(p>0.05). In terms of Vintage MP ceramic, it was in the $Starloy{(R)}\;C$ alloys that the high shear bond strength was showed and statistically significant differences(p<0.05). Metal-ceramic to fracture of the shear strength measurements and an analysis of all aspects of military usage fracture of the composite, respectively.

• Journal of Korean Tunnelling and Underground Space Association
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• v.9 no.2
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• pp.121-131
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• 2007

Recently, the probability of rock joints being exposed to free faces is getting higher for the scale of rock mass structures gets larger. Also, the frequency of occurring dynamic events such as earthquakes and blasting has been increasing. Thus, the shear behavior of rock joints under different conditions needs to be investigated. In this study, a series of direct shear tests were carried out under various conditions to examine the velocity-dependent shear behavior of saw-cut rock joints. Two types of direct shear test were carried out. The first was to examine the velocity-dependent shear behavior of saw-cut rock joints at seven different shear velocities, each with three different normal stresses. The second was to examine the shear behavior of saw-cut rock joints when three different instantaneous shear velocities changed. As a result, the coefficient of friction was affected by normal stress. The breakpoint velocity, the point when the change of shear velocity starts to affect the frictional behavior, became lower as normal stress increased. Also, as the shear velocity became lower, the degree of stress-drop on stick-slip behavior became larger. As a result of examining the changes of friction coefficient, velocity weakening (decrease of friction coefficient) was observed. The decrement of friction coefficient due to the changes of shear velocity under slow shear velocity was larger than that under fast shear velocity.

• Journal of Korean Tunnelling and Underground Space Association
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• v.11 no.1
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• pp.71-83
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• 2009

Shotcrete is an important primary support for tunnelling in rock. The quality control of shotcrete is a core issue in the safe construction and maintenance of tunnels. Although shotcrete may be applied well initially onto excavated rock surfaces, it is affected by blasting, rock deformation and shrinkage and can debond from the excavated surface, causing problems such as corrosion, buckling, fracturing and the creation of internal voids. This study suggests an effective non-destructive evaluation method of the tunnel shotcrete bonding state applied onto hard rocks using the impact-echo (IE) method and ground penetration radar (GPR). To verify previous numerical simulation results, experimental study carried out. Generally, the bonding state of shotcrete can be classified into void, debonded, and fully bonded. In the laboratory, three different bonding conditions were modeled. The signals obtained from the experimental IE tests were analyzed at the time domain, frequency domain, and time-frequency domain (i.e., the Short- Time Fourier transform). For all cases in the analyses, the experimental test results were in good agreement with the previous numerical simulation results, verifying this approach. Both the numerical and experimental results suggest that the bonding state of shotcrete can be evaluated through changes in the resonance frequency and geometric damping ratio in a frequency domain analysis, and through changes in the contour shape and correlation coefficient in a time-frequency analysis: as the bonding state worsens in hard rock condition, the autospectral density increases, the geometric damping ratio decreases, and the contour shape in the time-frequency domain has a long tail parallel to the time axis. The correlation coefficient can be effectively applied for a quantitative evaluation of bonding state of tunnel shotcrete. Finally, the bonding state of shotcrete can be successfully evaluated based on the process suggested in this study.