• Computers and Concrete
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• v.24 no.3
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• pp.207-222
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• 2019

This paper has presented an effective and accurate meso-scale finite element model for simulating the fracture process of concrete under compression-shear loading. In the proposed model, concrete is parted into four important phases: aggregates, cement matrix, interfacial transition zone (ITZ), and the initial defects. Aggregate particles were modelled as randomly distributed polygons with a varying size according to the sieve curve developed by Fuller and Thompson. With regard to initial defects, only voids are considered. Cohesive elements with zero thickness are inserted into the initial mesh of cement matrix and along the interface between aggregate and cement matrix to simulate the cracking process of concrete. The constitutive model provided by ABAQUS is modified based on Wang's experiment and used to describe the failure behaviour of cohesive elements. User defined programs for aggregate delivery, cohesive element insertion and modified facture constitutive model are developed based on Python language, and embedded into the commercial FEM package ABAQUS. The effectiveness and accuracy of the proposed model are firstly identified by comparing the numerical results with the experimental ones, and then it is used to investigate the effect of meso-structure on the macro behavior of concrete. The shear strength of concrete under different pressures is also involved in this study, which could provide a reference for the macroscopic simulation of concrete component under shear force.

• Restorative Dentistry and Endodontics
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• v.24 no.2
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• pp.408-415
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• 1999

When a zinc-oxide eugenol type sealer was placed in root canals treated previously with calcium hydroxide, acceleration of its setting and the yellowish discoloration were observed clinically. The purpose of this study was to evaluate the properties of calcium hydroxide-eugenol compound. Some physical properties of calcium hydroxide-eugenol compound were compared with a manufactured zinc-oxide eugenol based root canal sealer, Tubli-seal$^{(R)}$ in terms of water solubility, water sorption, film thickness and microleakage. Solubility and water sorption were determined by the use of the method described in American Dental Association Specification(ADAS) no. 57. Ten samples of each material were prepared into disks 20mm in diameter and 1.5mm in thickness. The samples were immersed in 50ml of distilled water at $37{\pm}1^{\circ}C$ for 7 days. The samples were then removed and placed in a desiccator. The values for solubility and water sorption were calculated using differences between the weights of same sample. Film thickness was determined by the use of the method described in ADAS no. 57 too. A small quantity of mixed cement was placed between two glass plates of which thickness was measured previously. 15Kg loading was applied and total thickness of the glass plates and the cement film was measured. The thickness difference was recorded as the material's film thickness. Microleakage was determined with a dye penetration method. Experimental materials were placed between the dentin surface of bovine tooth and the acrylic rod. These units were immersed in Pelican ink (W-Germany) for three days. Dye-penetrated dentin surfaces of bovine tooth were measured using the NIB Image 1.60 Macintosh program. The results are as follows: 1. Water solubility value of calcium hydroxide-eugenol compound (20.98${\pm}$2.94%) was statistically higher than those of Tubli-seal$^{(R)}$(2.52${\pm}$0.49%)(p<0.05). 2. Water sorption value of calcium hydroxide-eugenol compound (59.72${\pm}$17.75%) was statistically higher than those of Tubli-seal$^{(R)}$(3.15${\pm}$0.76%)(p<0.05). 3. Film thickness value of calcium hydroxide-eugenol compound (0.36${\pm}$0.03mm) was statistically higher than those of Tubli-seal$^{(R)}$(0.12${\pm}$0.1mm)(p<0.05). 4. Dye penetration value after 3 days-immersion of calcium hydroxide-eugenol compound(57.63${\pm}$25.85%) was statistically higher than those of Tubli-seal$^{(R)}$(28.05${\pm}$23.46%)(p<0.05).

• Journal of Dental Rehabilitation and Applied Science
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• v.27 no.3
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• pp.253-265
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• 2011

When restoring endodontically treated teeth is the mismatch between fiber post size and post space diameter, the resin cement layer is excessively thick in post space and voids are likely to form in it, thus predisposing to de-bonding. The method to overcome this problem is to reline the fiber post with composite resin. This individual anatomic post improves the adaptation of post to root walls and decreases the resin cement thickness. The purpose of this in vivo study was to evaluate the push-out bond strength of fiber post according to relining procedure and luting agents type used for simplicity of clinical procedure. Forty-two extracted teeth were divides into six groups.(n=7) A1: relined fiber post cemented with Luxacore/all-bons 2, A2: non-relined fiber post cemented with Luxacore/all-bond2, B1: relinind fiber post cemented with Calibra/XP-bond, B2: non-relined fiber post cemented with Calibra/XP-bond, C1: relined fiber post cemented with RelyX Unicem, C2: non-relined fiber post cemented with RelyX Unicem Push-out bond strength was affected by interaction between relining procedure and luting agent type. Relined fiber post presented higher push-out bond strength value than non-relined fiber post and statically significant differences(p<0.05) Cementation with RelyX Unicem showed significantly higher bond strength than other luting agents(p<0.05).

• Journal of Periodontal and Implant Science
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• v.45 no.1
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• pp.30-35
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• 2015

Purpose: Implant beds with an insufficient amount of cortical bone or a loss of cortical bone can result in the initial instability of a dental implant. Thus, the objective of this study was to evaluate the effect of bone cement grafting on implant initial stability in areas with insufficient cortical bone. Methods: Two different circumferential defect depths (2.5 mm and 5 mm) and a control (no defect) were prepared in six bovine rib bones. Fourteen implants of the same type and size ($4mm{\pm}10mm$) were placed in each group. The thickness of the cortical bone was measured for each defect. After the implant stability quotient (ISQ) values were measured three times in four different directions, bone cement was grafted to increase the primary stability of the otherwise unstable implant. After grafting, the ISQ values were measured again. Results: As defect depth increased, the ISQ value decreased. In the controls, the ISQ value was $85.45{\pm}3.36$ ($mean{\pm}standard$ deviation). In circumferential 2.5-mm and 5-mm defect groups, the ISQ values were $69.42{\pm}7.06$ and $57.43{\pm}6.87$, respectively, before grafting. These three values were significantly different (P<0.001). After grafting the bone cement, the ISQ values significantly increased to $73.72{\pm}8.00$ and $67.88{\pm}10.09$ in the 2.5-mm and 5.0-mm defect groups, respectively (P<0.05 and P<0.001). The ISQ value increased to more than double that before grafting in the circumferential 5-mm defect group. The ISQ values did not significantly differ when measured in any of the four directions. Conclusions: The use of bone cement remarkably increased the stability of the implant that otherwise had an insufficient level of stability at placement, which was caused by insufficient cortical bone volume.

• Journal of Dental Rehabilitation and Applied Science
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• v.24 no.4
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• pp.317-324
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• 2008

The objective of this study was to test effects of (1) where the occlusal contact points locate on a full veneer crown, and (2) which direction the contact forces are directed to, on the stresses within the luting cement layer that might suffer microfracture. A total of 27 finite element models were created for a mandibular first molar, combining 9 different locations of the occlusal contact points and 3 different loading directions. Type 3 gold alloy was used for crown material with a chamfer margin, and the luting cement material was glass ionomer cements in uniform thickness of $75{\mu}m$. Modeled crowns were loaded at 100 N. Different patterns in the cement stress were observed in the vicinity of the buccal and lingual margins. Whereas, the peak stress in buccal margin occurred approximately 0.5 mm away from the external surface, the highest stress in lingual margin was observed at approximately 1 mm. Significantly different distribution of stresses was recorded as a function either of the location of the occlusal contact points or of the loading direction. Higher stresses were produced by more obliquely acting load, and when the loaded point was in the vicinity of the cusp tip.

• Journal of the korean academy of Pediatric Dentistry
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• v.46 no.3
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• pp.318-327
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• 2019

The purpose of this study was to identify which combination of zirconia crowns and cements is most similar in color to the maxillary primary incisors by varying the color of zirconia crowns, crown thickness, and shade of cements. Prefabricated zirconia crowns in 3 shades and crowns fabricated using 6 types of zirconia blocks were used in this study. These were filled with A2-shade or translucent-shade resin cement and the $L^*$, $a^*$, and $b^*$ values were calculated using a spectrophotometer. The color differences between the natural teeth and the zirconia crowns were assessed. The shade of the final restoration was more similar to that of the natural teeth using A2-shade than translucent-shade resin cement. Application of A2-shade cement to a 0.5-mm-thick crown fabricated from a smile series 2 zirconia block resulted in the color most similar to that of the natural teeth. A2-shade resin cement is recommended for zirconia crown restoration in anterior primary teeth compared to TR-shade resin cement for more esthetic restoration. Since restorations with Nu-smile zirconia crowns were not esthetically favorable in terms of shade, improvement of the shade characteristics of the product or development of a new kind of zirconia crown is required.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.4
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• pp.483-489
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• 2020

Particulate matter is divided into PM10 (particle diameter of 10 ㎛ or less) and PM2.5 (particle diameter of 2.5 ㎛ or less), which are approximately 1/5 of the thickness of the hair. Due to its effect on the human body, lung disease, arteriosclerosis and heart It is known as a carcinogen that causes various diseases such as diseases. It is known that the main cause of such fine dust is nitrogen dioxide (NOx), which is emitted from automobiles in about 57.3% of urban roadsides. Therefore, in this study, as part of the development of functional construction materials to reduce NOx generated from road transport pollutants, comparative evaluation of NOx reduction performance was conducted according to the replacement rate of cement mortar in which cement was replaced with a porous material. In addition, the NOx reduction performance of cement mortar according to the photocatalyst application method and the number of applications was compared an d evaluated. As a result of the experiment, when activated ocher was substituted by 30%, it showed a reduction effect of about 32.7%, showing the best reduction performance.

• KIEAE Journal
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• v.9 no.6
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• pp.13-18
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• 2009

Korean traditional houses have been developed in harmony with natural environment and comfortable indoor condition by using the natural resources including building layout, space composition and materials. Originally Korea traditional architectures have used wood lintel constructions and loess walls through the many years. Theses loess have many strength such as highly heat capacity, controling of humidity, a deodorant than any other materials. Nowaday it is recommended to use exterior and interior walls in loess wall to meet the eco-friendly materials to improve our residental environmental. Thus this study aims to research the sound insulation performance of traditional loess brick wall varied with thickness, thermal insulation materials and cavity wall. The sound insulation performance of these loess walls are compared with other masonry wall's and sound insulation performance of th walls were tested in anechoic laboratory to measure the sound transmission loss of these walls. The loess brick wall with 75mm thickness of cavity is shown the sound insulation performance with Rw 57 which is nearly same performances of 1B brick wall and cement 8' block wall, The improving effect of insulation materials is shown in the high frequency bandwidth. Especially, there is improving as much as 11 dB using the extruded poly stylene form(75mm) and poly ethylene film(0.7mm).

• Geomechanics and Engineering
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• v.10 no.6
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• pp.827-836
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• 2016

The rate of softening is an important factor to determine whether the failure occurs along localized shear band or in a more diffused manner. In this paper, strength loss and softening rate effect depending on sensitivity are investigated for weakly cemented clays, for both artificially cemented high plasticity San Francisco Bay Mud and low plasticity Yolo Loam. Destructuration and softening behavior for weakly cemented sensitive clays are demonstrated and discussed through multiple vane shear tests. Artificial sensitive clays are prepared in the laboratory for physical modeling or constitutive modeling using a small amount of cement (2 to 5%) with controlled initial water content and curing period. Through test results, shear band thickness is theoretically computed and the rate of softening is represented as a newly introduced parameter, ${\omega}_{80%}$. Consequently, it is found that the softening rate increases with sensitivity for weakly cemented sensitive clays. Increased softening rate represents faster strength loss to residual state and faster minimizing of shear band thickness. Uncemented clay has very low softening rate to 80% strength drop. Also, it is found that higher brittleness index ($I_b$) relatively shows faster softening rate. The result would be beneficial to study of physical modeling for sensitive clays in that artificially constructed high sensitivity (up to $S_t=23$) clay exhibits faster strain softening, which results in localized shear band failure once it is remolded.

• Restorative Dentistry and Endodontics
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• v.20 no.1
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• pp.303-315
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• 1995

An adequate and homogeneous cure of light-activated restroative material is very important for improvement of marginal adaptation and prevention of marginal leakage, secondary caries and pulpal irritation as well as expressing natural physical property of that material. The purpose of this study was to evaluate the change of surface hardness and cure uniformity of light-activated glass ionomer cements. Restorative(Fuji II LC, Vitremer) and lining(Baseline VLC, Vitrebond) light-activated glass ionomer cements were investigated for this study. The surface hardness of the top and bottom surfaces and cure uniformity of each 1mm, 1.5mm, 2mm, 2.5mm & 3mm in the thickness of specimen were measured immediately, at 1 hour, 24 hours and 1 week after light activation. The surface hardness change and cure uniformity of all the specimens were measured by Knoop hardness tester. The results were as follows. 1. The surface hardness of top and bottom surfaces in all groups increased with time(p<0.01). 2. Both top and bottom surfaces hardness of Vitrebond group measured immediately after light-activation were significantly lower than those of the other groups(p<0.01). 3. The surface hardness of top and bottom surfaces of restorative light -activated glass ionomer cements was higher than those of lining materials at 1 week(p<0.10). 4. Surface hardness of Vitremer group decreased as the specimen thickness increased, except top and bottom surfaces hardness of the specimen at 1 week(p<0.01). There was no significant difference in the surface hardness of Fuji II LC with changes in the thickness except bottom surface hardness of specimen at 24 hours and 1 week (p>0.05). 5. Surface hardness of Vitrebond group significantly decreased as the specimen thickness increased(p<0.01). There was no significant difference in the surface hardness of Baseline VLC group with changes in the thickness except bottom surface hardness of specimen measured immediately after light -activation(p>0.05). 6. The hardness ratio of top against bottom surface in all groups decreased with time(p<0.05). 7. There was no significant difference in the hardness ratio of top against bottom surface with changes of the thickness except Vitrebond group, 24 hours and 1 week of Vitremer group and 1 week of Baseline VLC group (p>0.05). These results suggest that surface hardness of restorative ligh-activated glass ionomer cements were highter than those of lining light-activated materials. In all groups, the surface hardness and cure uniformity continuously increased with time.