• Journal of Dental Rehabilitation and Applied Science
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• v.32 no.1
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• pp.24-31
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• 2016

Purpose: Many studies have shown that airborne-particle abrasion of fiber post can improve the bonding strength to resin cement. But, airborne-particle abrasion may influence the property of fiber post. The purpose of this study is to evaluate the influence of airborne-particle abrasion on flexural strength of fiber post. Materials and Methods: Two fiber-reinforced posts; DT Light Post Size 2 (1.8 mm diameter, Bisco Inc) and RelyX Fiber Post Size 3 (1.9 mm diameter, 3M ESPE); were used in this study. Each group was divided into 3 subgroups according to different surface treatments; without pretreatment: $50{\mu}m$ aluminum oxide (Cobra$^{(R)}$, Renfert): and $30{\mu}m$ aluminum oxide modified with silica (Rocatec Soft$^{(R)}$, 3M ESPE). After airborne-particle abrasion procedure, three-point bending test was done to determine the flexural strength and flexural modulus. The diameter of each posts was measured to an accuracy of 0.01 mm using a digital micrometer. There was no diameter change before and after airborneparticle abrasion. The mean flexural moduli and flexural strengths calculated using the appropriate equations. The results were statistically analyzed using One-way ANOVA and Scheffe's post-hoc test at 95% confidencial level. Results: There was no significant difference on flexural strength between groups. Conclusion: In the limitation of this study, flexural strength and flexural modulus of fiber post are not affected by airborne-particle abrasion.

• Steel and Composite Structures
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• v.23 no.5
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• pp.543-555
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• 2017

The mechanical properties of steel fiber reinforced high strength concrete (SFRHSC) made with binary and ternary blends of metakaolin (MK) and ground pumice (GP) are investigated in this study. The investigated properties are ultrasonic pulse velocity ($U_{pv}$), compressive strength ($f_c$), flexural strength ($f_f$) and splitting tensile strength ($f_{st}$) of SFRHSC. A total of 16 steel fiber reinforced concrete mixtures were produced by a total binder content of $500kg/m^3$ for determining the effects of MK and GP on the mechanical properties. The design $f_c$ was acquired from 70 to 100 MPa by using a low water-binder ratio of 0.2. The test results exhibit that high strength concrete can be obtained by replacing the cement with MK and GP. Besides, correlations between these results are executed for comprehending the relationship between mechanical properties of SFRHSC and the strong correlations are observed between these properties. Moreover, two models in the gene expression programming (GEP) for predicting the $f_c$ of SFRHSC made with binary and ternary blends of MK and GP have been developed. The results obtained from these models are compared with the experimental results. These comparisons proved that the results of equations obtained from these models seem to agree with the experimental results.

• The Journal of the Korean dental association
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• v.51 no.11
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• pp.595-603
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• 2013

The requirements for the successful treatment of all-ceramic restorations are not so different from the ones of conventional restorations. "The provisional restoration followed by an adequate tooth reduction and the accurately fitting prostheses with corresponding to final impression" can be the examples of them. Nevertheless, the one which all-ceramic restorations are distinguished from conventional restorations is the additional procedure of so called "bonding". In addition to the application of resin cement between "inner surface of restoration and outer surface of abutment", bonding technology can be also applied to the treatment process of "Post and Core" in particular if the abutments are non-vital teeth. Core build-up for all-ceramic crown is conducted with fiber post and tooth colored composite by considering the properties of the restorations transmitting light. We know well that a vital abutment is easier than a non-vital one to get the targeted goals for clinical success in connection with esthetics and structure. The creation of "Post and Core" with bonding technique is a decisive factor for a long-term success if the abutment is non-vital tooth with dentinal collapse. I would like to share my clinical experience about "post & core build-up and all-ceramic restoration bonding" out of several success strategies of all-ceramic crown with this presentation.

• The Journal of the Korean dental association
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• v.48 no.4
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• pp.297-307
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• 2010

Noncarious cervical lesions(NCCLs) are characterized as structural defects found on the tooth surface of the cement-enamel junction. Loss of tooth structure through noncarious mechanisms may vary in etiology and clinical presentation for each individual but presently many clinician now classify this as tooth failure of abfraction due to the stress applied in the cervical area of the tooth under oral physiological and pathological loads. In the current study, we investigated the stress distribution of maxillary premolar with NCCL using simulated 3D finite element analysis. The results were as follows: 1. In the sound maxillary premolar, the stresses were highly concentrated at cervical enamel surface of the mesiobuccal line angle, asymmetrically. 2. Once the lesion has been formed, the highest stress concentration was observed around the apex of the wedge shaped lesion. 3. In four types of NCCL, the patterns of stress distribution were similar and the peak stress was observed at mesial corner and also stresses concentrated at lesion apex. 4. Lesion cavity modification of rounding apex, reduced stress of lesion apex. 5. When restoring the notch-shaped lesion, material with high elastic modulus worked well at the lesion apex and material with low elastic modulus worked well at the cervical cavosurface margin.

• Corrosion Science and Technology
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• v.22 no.4
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• pp.273-286
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• 2023

Rebar is embedded in concrete to create reinforced concrete (RC). Rebar carries most of the tensile stress and gives compressively loaded concrete fracture resistance. However, embedded steel corrosion is a significant cause of concern for RC composite structures worldwide. It is one of the biggest threats to concrete structures' longevity. Due to environmental factors, concrete decays and reinforced concrete buildings fail. The type and surface arrangement of the rebar, the cement used in the mortar, the dosing frequency of the concrete, its penetrability, gaps and cracks, humidity, and, most importantly, pollutants and aggressive species all affect rebar corrosion. Either carbonation or chlorides typically cause steel corrosion in concrete. Carbonation occurs when carbon dioxide in the atmosphere combines with calcium within the concrete. This indicates that the pH of the medium is falling, and the steel rebar is corroding. When chlorides pass through concrete to steel, corrosion rates skyrocket. Consideration must be given to concrete moisture. Owing to its excellent resistance, dry concrete has a low steel corrosion rate, whereas extremely wet concrete has a low rate owing to delayed O₂ transfer to steel surfaces. This paper examines rebar corrosion causes and mechanisms and describes corrosion evaluation and mitigation methods.

• Journal of Korean society of Dental Hygiene
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• v.13 no.2
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• pp.351-360
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• 2013

Objectives : The purpose of this study was to evaluate the effects of tooth bleaching agent contained 15% carbamide peroxide on the color, microhardness and surface roughness of tooth-colored restorative materials by using pH cycling model. Methods : Four types of tooth-colored restorative materials, including a composite resin(Filtek Z350 ; Z350), a flowable composite resin(Filtek P60 : P60), a compomer(Dyract$^{(R)}$ AP ; DY), and a glass-ionomer cement(KetacTM Molar Easymix ; KM). were used in the study. Eighty-eight specimens of each material were fabricated, randomly divided into two groups(n=44): experimental group(15% carbamide peroxide) and control group(distilled water). These groups were then divided into four subgroups(n=11). All groups were bleached 4 hours per day for 14 days using pH cycling model. The authors measured the color, microhardness, and roughness of the specimens before and after bleaching. The data were analyzed with ANOVA and T-test. Results : Z350 and P60 showed a slight color change(${\Delta}E^*$), whereas DY and KM showed significantly color change(p<0.05). Among them, the greatest color change was observed in DY. Percentage microhardness loss(PML) of the distilled water group was 1.8 to 5.1%, and 15% peroxide peroxide group was 5.0 to 25.2%. Microhardness of DY and KM showed a statistically significant decrease(p<0.05). Roughness was increased in all groups after bleaching. Z350 and P60 does not have a significant difference(p>0.05), however DY and KM significantly increased more than the 0.2 ${\mu}m$(p<0.05). Conclusions : The effects of bleaching on restorative materials were material dependent. It is necessary to consider the type of the material before starting the treatment.

• Journal of the korean academy of Pediatric Dentistry
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• v.48 no.2
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• pp.168-175
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• 2021

This study compared the microleakages and compressive strengths of various base materials. To evaluate microleakages, 50 extracted permanent premolars were prepared. The teeth divided into 5 groups of 10 each according to the base materials. Cavities with a 5.0 mm width, 3.0 mm length, and 3.0 mm depth were formed on the buccal surfaces of the teeth. After filling the cavities with different base materials, a composite resin was used for final restoration. Each specimen was immersed in 2% methylene blue solution and then observed under a stereoscopic microscope (× 30). To evaluate the compressive strength, 5 cylindrical specimens were prepared for each base material. A universal testing machine was used to measure the compressive strength. The microleakage was highest in the Riva light cure^TM group and lowest in the Biodentine^TM and Well-Root^TM PT groups. For the compressive strengths, in all groups, acceptable strength values for base materials were found. The highest compressive strength was observed in the Fuji II LC^TM group and the lowest strength in the Well-Root^TM PT group.

• Journal of the Korea Institute of Building Construction
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• v.11 no.2
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• pp.127-135
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• 2011

In this study, the engineering characteristics of outer wall insulation panels according to type of insulation materials, their combination, and the contents of insulation materials were tested. Vermiculate, ceramic bead, perlite and expanded polystyrene were used as insulation materials. Flexural strength and thermal conductivity depending on the insulation materials used were measured. It was found that the flow of fresh mortar significantly decreased with an increase in the contents of insulation materials. In terms of the effect of insulation materials on thermal conductivity, an increase in insulation materials resulted in a decrease of thermal conductivity. In particular, PL and EPS, when used together, have lower thermal conductivity than other materials. Regarding the flexural strength of the hardened mortar, the strength showed a tendency to gradually decrease according to the increase in contents of insulation materials, compared to that of the plain mortar. In terms of the flexural strength depending on various types of insulation materials and its combination, it was found that the flexural strength of cement mortar containing 3% of vermiculate(V)+ceramic bead(CB)+perlite(PL) was the highest among the specimens tested.

• The Journal of Korean Academy of Prosthodontics
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• v.36 no.2
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• pp.273-292
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• 1998

The purpose of this study was to evaluate marginal fit of four all-ceramic crown systems 1) conventional In-Ceram, 2) copy-milled In-Ceram using Celay system, 3) IPS Empress, 4) OPC(Optimal Pressable Ceramic). All ceramic crowns were made on epoxy dies. The fabricated crowns were sandblasted, cleaned with ultrasonic cleansing, silanated, and cemented with Bistite composite resin cement. the selected marginal areas of the crowns were the labial, lingual, mesial, and distal surface. Each selected area of surface was $0.6{\times}1.6mm$ in dimension. The image of each marginal area was captured to computer files using DT-55 Frame Grabber and light microscope connected CCD camera. The marginal gaps were measured every $70{\mu}m$ using computer image analysis program. The results obtained were summarized as follows : 1. The marginal fit of four all-ceramic crowns were significantly different from each other(p<0.01), and mean marginal fit values obtained were $31.42{\pm}16.52{\mu}m$ in conventional In-Ceram, $55.45{\pm}27.90{\mu}m$ in copy-milled In-Ceram using Celay system, $44.36{\pm}24.59{\mu}m$ in IPS Empress, $47.21{\pm}20.42{\mu}m$ in OPC. 2. In the marginal fit of conventional In-Ceraw and copy-milled In-Ceram crowns using Celay system there was no significant difference between mesiodistal and buccolingual surface, but in the marginal fit of IPS Empress and OPC crowns, there was significant difference between mesiodistal and buccolingual surface(p<0.01). 3. The marginal fit of four kinds of all-ceramic crowns was clinically acceptable.

• Journal of the korean academy of Pediatric Dentistry
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• v.42 no.3
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• pp.249-256
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• 2015

Restorative dental materials have advanced rapidly, with improved physical properties that improve survival rates. Accordingly, various materials can be selected. Amalgam, composite resin, glass-ionomer cement, and preformed stainless steel crowns have all been used widely for the restoration of dental caries in primary molars. The various dental materials used to treat proximal caries in the primary molars have distinct advantages and disadvantages. However, few studies have examined their survival rates. This retrospective study examined the 2-year survival rates of more than 700 class II restorations of proximal caries in primary molars clinically and radiologically according to the type of restoration. The study results should help in the selection of class II restorations for molars, one of the biggest concerns of pediatric dentists.