• The Journal of Korean Academy of Prosthodontics
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• v.46 no.3
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• pp.290-297
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• 2008

STATEMENT OF PROBLEM: Implant-supported fixed cantilever prostheses are influenced by various biomechanical factors. The information that shows the effect of implant number and position of cantilever on stress in the supporting bone is limited. PURPOSE: The purpose of this study was to investigate the effect of implant number variation and the effect of 2 different cantilever types on stress distribution in the supporting bone, using 3-dimensional finite element analysis. MATERIAL AND METHODS: A 3-D FE model of a mandibular section of bone with a missing second premolar, first molar, and second molar was developed. $4.1{\times}10$ mm screw-type dental implant was selected. 4.0 mm height solid abutments were fixed over all implant fixtures. Type III gold alloy was selected for implant-supported fixed prostheses. For mesial cantilever test, model 1-1 which has three $4.1{\times}10$ mm implants and fixed prosthesis with no pontic, model 1-2 which has two $4.1{\times}10$ mm implants and fixed prosthesis with a central pontic and model 1-3 which has two $4.1{\times}10$ mm implants and fixed prosthesis with mesial cantilever were simulated. And then, 155N oblique force was applied to the buccal cusp of second premolar. For distal cantilever test, model 2-1 which has three $4.1{\times}10$ mm implants and fixed prosthesis with no pontic, model 2-2 which has two $4.1{\times}10$ mm implants and fixed prosthesis with a central pontic and model 2-3 which has two $4.1{\times}10$ mm implants and fixed prosthesis with distal cantilever were simulated. And then, 206N oblique force was applied to the buccal cusp of second premolar. The implant and superstructure were simulated in finite element software(Pro/Engineer wildfire 2.0). The stress values were observed with the maximum von Mises stresses. RESULTS: Among the models without a cantilever, model 1-1 and 2-1 which had three implants, showed lower stress than model 1-2 and 2-2 which had two implants. Although model 2-1 was applied with 206N, it showed lower stress than model 1-2 which was applied with 155N. In models that implant positions of models were same, the amount of applied occlusal load largely influenced the maximum von Mises stress. Model 1-1, 1-2 and 1-3, which were loaded with 155N, showed less stress than corresponding model 2-1, 2-2 and 2- 3 which were loaded with 206N. For the same number of implants, the existence of a cantilever induced the obvious increase of maximum stress. Model 1-3 and 2-3 which had a cantilever, showed much higher stress than the others which had no cantilever. In all models, the von Mises stresses were concentrated at the cortical bone around the cervical region of the implants. Meanwhile, in model 1-1, 1-2 and 1-3, which were loaded on second premolar position, the first premolar participated in stress distribution. First premolars of model 2-1, 2-2 and 2-3 did not participate in stress distribution. CONCLUSION: 1. The more implants supported, the less stress was induced, regardless of applied occlusal loads. 2. The maximum von Mises stress in the bone of the implant-supported three unit fixed dental prosthesis with a mesial cantilever was 1.38 times that with a central pontic. The maximum von Mises stress in the bone of the implant-supported three-unit fixed dental prosthesis with a distal cantilever was 1.59 times that with a central pontic. 3. A distal cantilever induced larger stress in the bone than a mesial cantilever. 4. A adjacent tooth which contacts implant-supported fixed prosthesis participated in the stress distribution.

• Journal of the Korea Institute of Building Construction
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• v.9 no.4
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• pp.55-61
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• 2009

Recently, the number of high-rise buildings being built in Korea by major construction companies for residential and commercial use has been increasing. When constructing a high-rise building, it is necessary to apply massive amounts of concrete to form a mat foundation that can withstand the huge load of the upper structure. However, it is of increasing concern that due to limitations in terms of the amount of placing equipment, available job-sites and systems for mass concrete placement in the construction field, it is not always possible to place a great quantity of concrete simultaneously in a large-scale mat foundation, and for this reason consistency between placement lift cannot be secured. In addition, a mat foundation Is likely to crack due to the stress caused by differences inhydration heat generation time. To derive a solution for these problems, this study provides test results of a hydration heat crack reduction method by applying placement lift change and setting time control with a super retarding agent for mass concrete in a large-scale mat foundation. Mock-up specimens with different mixtures and placement liftswere prepared at the job-site of a newly-constructed high-rise building. The test results show that slump flow of concrete before and after adding the super retarding agent somewhat Increases as the target retarding time gets longer, while the air content shows no great difference. The setting time was observed to be retarded as the target retarding time gets longer. As the target retarding time gets longer, compressive strength appears to be decreased at an early stage, but as time goes by, compressive strength gets higher, and the compressive strength at 28 days becomes equal or higher to that of plain concrete without a super retarding agent. For the effect of placement lift change and super retarding agent on the reduction of hydration heat, the application of 2 and 4 placement lifts and a super retarding agent makes it possible to secure consistency and reduce temperature difference between placement lifts, while also extending the time to reach peak temperature. This implies that the possibility of thermal crack induced by hydration heat is reduced. The best results are shown in the case of applying 4 placement lifts.

• Journal of Dental Rehabilitation and Applied Science
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• v.26 no.4
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• pp.405-417
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• 2010

Previous studies have already shown that mouthguard is effective in protecting jaw bone, teeth and oral tissue against sports trauma. However, other than severe trauma, repetitive force, such as disorders like clenching, cause teeth or oral tissue damage. These kinds of disorders usually present pathologic attrition in the posterior teeth, resorption in alveolar bone, loss of teeth and destruction of occlusion. Wearing a mouthguard is believed to be effective in preventing these disorders. But its effect is not examined thoroughly enough. The purpose of this study is to identify whether mouthguard is effective in reducing strain caused by clenching. Mandibular first molars in the normal occlusal relationship without any history of dental treatment were chosen. Biaxial type strain gauge was placed on the buccal surface of the tooth. Having maximum occlusal force, measured by load cell, as a standard, clenching intensity were divided into three stages; moment of slightly tooth contact, medium bite force (50% of maximum bite force), maximum bite force. Strain occurring in dentition in each stage with and without mouthguard was measured. Changes in strain (on dentition) between each stage and difference in strain, between with or without mouthguard were recorded by PCD-300 analyzer and PCD-30 soft ware. The data was statistically analyzed by Wilcoxon signed rank test. The following results were drawn; Without mouthguard, strain given on dentition increased as the clenching force increased. With mouthguard, strain given on dentition also increased as the clenching force increased. With mouthguard, strain decreased, in all cases of clenching force stages. Data on the moment of slightly tooth contact stage, had no statistical significance. However, with mouthguard, 50-90% of decrease in strain could be obtained in maximum occlusal force, compared to the group without mouthguard. Mouthguard decreased the strain on the dentition, caused by clenching. Therefore, mouthguard seems to be effective in preventing damage on dentition, by acting against clenching, which occurs both consciously and unconsciously during sports activities.

• Proceedings of the KACD Conference
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• 2008.05a
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• pp.177-183
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• 2008

It was reported that esthetic composite resin restoration reinforces the strength of remaining tooth structure with preserving the natural tooth structure. However, it is unknown how much the strength would be recovered. The purpose of this study was to compare the fracture resistance of three types of undermined cavity filled with composite resin with that of non-cavitated natural tooth. Forty sound upper molars were allocated randomly into four groups of 10 teeth. After flattening occlusal enamel. undermined cavities were prepared in thirty teeth to make three types of specimens with various thickness of occlusal structure (Group $1{\sim}3$). All the cavity have the 5 mm width mesio-distally and 7 mm depth bucco-lingually. Another natural 10 teeth (Group 4) were used as a control group. Teeth in group 1 have remaining occlusal structure about 1 mm thickness, which was composed of mainly enamel and small amount of dentin. In Group 2, remained thickness was about 1.5 mm, including 0.5 mm thickness dentin. In Group 3, thickness was about 2.0 mm, including 1 mm thickness dentin. Every effort was made to keep the remaining dentin thickness about 0.5 mm from the pulp space in cavitated groups. All the thickness was evaluated with radiographic Length Analyzer program. After acid etching with 37% phosphoric acid, one-bottle adhesive (Single $Bond^{TM}$, 3M/ESPE, USA) was applied following the manufacturer's recommendation and cavities were incrementally filled with hybrid composite resin (Filtek $Z-250^{TM}$, 3M/ESPE, USA). Teeth were stored in distilled water for one day at room temperature, after then, they were finished and polished with Sof-Lex system. All specimens were embedded in acrylic resin and static load was applied to the specimens with a 3 mm diameter stainless steel rod in an Universal testing machine and cross-head speed was 1 mm/min. Maximum load in case of fracture was recorded for each specimen. The data were statistically analyzed using one-way analysis of variance (ANOVA) and a Tukey test at the 95% confidence level. The results were as follows: 1. Fracture resistance of the undermined cavity filled with composite resin was about 75% of the natural tooth. 2. No significant difference on fracture loads of composite resin restoration was found among the three types of cavitated groups. Within the limits of this study, it can be concluded the fracture resistance of the undermined cavity filled with composite resin was lower than that of natural teeth, however remaining tooth structure may be supported and saved by the reinforcement with adhesive restoration, even of that portion consists of mainly enamel and a little dentin structure.

• Restorative Dentistry and Endodontics
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• v.33 no.3
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• pp.177-183
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• 2008

It was reported that esthetic composite resin restoration reinforces the strength of remaining tooth structure with preserving the natural tooth structure. However, it is unknown how much the strength would be recovered. The purpose of this study was to compare the fracture resistance of three types of undermined cavity filled with composite resin with that of non-cavitated natural tooth. Forty sound upper molars were allocated randomly into four groups of 10 teeth. After flattening occlusal enamel, undermined cavities were prepared in thirty teeth to make three types of specimens with various thickness of occlusal structure (Group $1{\sim}3$). All the cavity have the 5 mm width mesiodistally and 7 mm depth bucco-lingually. Another natural 10 teeth (Group 4) were used as a control group. Teeth in group 1 have remaining occlusal structure about 1 mm thickness, which was composed of mainly enamel and small amount of dentin. In Group 2, remained thickness was about 1.5 mm, including 0.5 mm thickness dentin. In Group 3, thickness was about 2.0 mm, including 1 mm thickness dentin. Every effort was made to keep the remaining dentin thickness about 0.5 mm from the pulp space in cavitated groups. All the thickness was evaluated with radiographic Length Analyzer program. After acid etching with 37% phosphoric acid, one-bottle adhesive (Single $Bond^{TM}$, 3M/ESPE, USA) was applied following the manufacturer's recommendation and cavities were incrementally filled with hybrid composite resin (Filtek $Z-250^{TM}$, 3M/ESPE, USA). Teeth were stored in distilled water for one day at room temperature, after then, they were finished and polished with Sof-Lex system. All specimens were embedded in acrylic resin and static load was applied to the specimens with a 3 mm diameter stainless steel rod in an Universal testing machine and cross-head speed was 1 mm/min. Maximum load in case of fracture was recorded for each specimen. The data were statistically analyzed using one-way analysis of variance (ANOVA) and a Tukey test at the 95% confidence level. The results were as follows: 1. Fracture resistance of the undermined cavity filled with composite resin was about 75% of the natural tooth. 2. No significant difference in fracture loads of composite resin restoration was found among the three types of cavitated groups. Within the limits of this study, it can be concluded the fracture resistance of the undermined cavity filled with composite resin was lower than that of natural teeth, however remaining tooth structure may be supported and saved by the reinforcement with adhesive restoration, even if that portion consists of mainly enamel and a little dentin structure.

• The Journal of Korean Academy of Prosthodontics
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• v.47 no.3
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• pp.312-319
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• 2009

Statement of problem: Delamination of veneering porcelain from underlying ceramic substructures has been reported for zirconia-ceramic restorations. Colored zirconia cores for esthetics have been reported that their bond strength with veneered porcelain is weaker compared to white zirconia cores. Purpose: This study aimed to investigate the shear bond strength by manufacturing the veneering porcelain on the colored zirconia core, using the layering technique and heat-pressing technique, and to evaluate the clinical stability by comparing the result of this with that of conventional metal ceramic system. Material and methods: A Metal ceramic (MC) system was tested as a control group. The tested systems were Katana zirconia with CZR (ZB) and Katana Zirconia with NobelRondo Press (ZP). Thirty specimens, 10 for each system and control, were fabricated. Specimen disks, 3 mm high and 12 mm diameter, were fabricated with the lost-wax technique (MC) and the CAD-CAM (ZB and ZP). MC and ZB specimens were prepared using opaque and dentin veneering ceramics, veneered, 3 mm high and 2.8 mm in diameter, over the cores. ZP specimens were prepared using heat pressing ingots, 3 mm high and 2.8mm in diameter. The shear bond strength test was performed in a Shear bond test machine. Load was applied at a cross-head speed of 0.50 mm/min until failure. Mean shear bond strengths (MPa) were analyzed with the One-way ANOVA. After the shear bond test, fracture surfaces were examined by SEM. Results: The mean shear bond strengths (SD) in MPa were MC control 29.14 (2.26); ZB 29.48 (2.30); and ZP 29.51 (2.32). The shear bond strengths of the tested systems were not significantly different (P > .05). All groups presented cohesive and adhesive failures, and showed predominance of cohesive failures in ceramic veneers. Conclusion: 1. The shear bond strengths of the tested groups were not significantly different from the control group (P >.05). 2. There was no significant different between the layering technique and the heat pressing technique in the veneering methods on the colored zirconia core. 3. All groups presented cohesive and adhesive failures, and showed predominance of cohesive failures in ceramic veneers.

• The Journal of Korean Academy of Prosthodontics
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• v.53 no.4
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• pp.345-351
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• 2015

Purpose: The purpose of this study was to evaluate the proper axial thickness of zirconia abutment applied to implant in the anterior region. Materials and methods: Zirconia abutments were prepared at different axial wall thickness by processing pre-sintered zirconia blocks via CAD/CAM to obtain equal specimens. The abutments were each produced with a thickness of 0.5 mm (Group 1), 0.8 mm (Group 2), 1.2 mm (Group 3), or 1.5 mm (Group 4). The implant used in this study was a external connection type one (US, Osstem, Pussan, Korea) product and the zirconia abutment was prepared via replication of a cemented abutment. The crowns were prepared via CAM/CAM with a thickness of 1.5 mm and were cemented to the abutments using $RelyX^{TM}$ UniCem cement. A universal testing machine was used to apply load at 30 degrees and measure fracture strength of the zirconia abutment. Results: Fracture strength of the abutments for Group 1, Group 2, Group 3, and Group 4 were $236.00{\pm}67.55N$, $599.00{\pm}15.80N$, $588.20{\pm}33.18N$, and $97.83{\pm}98.13N$, respectively. Group 1 showed a significantly lower value, as compared to the other groups (independent Mann-Whitney U-test. P<.05). No significant differences were detected among Group 2, Group 3, and Group 4 (independent Mann-Whitney U-test. P>.05). Conclusion: Zirconia abutment requires optimal thickness for fracture resistance. Within the limitation of this study, > 0.8 mm thickness is recommended for zirconia abutment in anterior implants.

• The Journal of Korean Academy of Prosthodontics
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• v.52 no.4
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• pp.312-316
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• 2014

Purpose: The aim of this study was to compare the fracture toughness of currently available resin cements for zirconia restorations and evaluate the effect of water storage on fracture toughness of those resin cements. Materials and methods: Single-edge notched specimens ($3mm{\times}6mm{\times}25mm$) were prepared from three currently available dual cure resin cements for zirconia restorations (Panavia F 2.0, Clearfil SA luting and Zirconite). Each resin cement was divided into four groups: immersed in distilled water at $37^{\circ}C$ for 1 (Control group), 30, 90, or 180 days (n=5). Specimens were loaded in three point bending at a cross-head speed of 0.1 mm/s. The maximum load at specimen failure was recorded and the fracture toughness ($K_{IC}$) was calculated. Data were analyzed using one-way ANOVA and multiple comparison $Scheff{\acute{e}}$ test (${\alpha}$=.05). Results: In control group, the mean $K_{IC}$ was $3.41{\pm}0.64MN{\cdot}m^{-1.5}$ for Panavia F, 2.0, $3.07{\pm}0.41MN{\cdot}m^{-1.5}$ for Zirconite, $2.58{\pm}0.30MN{\cdot}m^{-1.5}$ for Clearfil SA luting respectively, but statistical analysis revealed no significant difference between them. Although a gradual decrease of $K_{IC}$ in Panavia F 2.0 and gradual increases of KIC in Clearfil SA luting and Zirconite were observed with storage time, there were no significant differences between immersion time for each cement. Conclusion: The resin cements for zirconia restorations exhibit much higher $K_{IC}$ values than conventional resin cements. The fracture toughness of resin cement for zirconia restoration would not be affected by water storage.

• Restorative Dentistry and Endodontics
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• v.36 no.5
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• pp.425-430
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• 2011

Objectives: This in vitro study investigated whether short-term application of calcium hydroxide in the root canal system for 1 and 4 wk affects the fracture strength of human permanent teeth. Materials and Methods: Thirty two mature human single rooted mandibular premolars in similar size and dentin thickness without decay or restorations were hand and rotary instrumented and 16 teeth vertically packed with calcium hydroxide paste and sealed coronally with caviton to imitate the endodontic procedure and the other 16 teeth was left empty as a control group. The apicies of all the samples were sealed with resin, submerged in normal saline and put in a storage box at $37^{\circ}C$ to mimic the oral environment. After 1 and 4 wk, 8 samples out of 16 samples from each group were removed from the storage box and fracture strength test was performed. The maximum load required to fracture the samples was recorded and data were analysed statistically by the two way ANOVA test at 5% significance level. Results: The mean fracture strengths of two groups after 1 wk and 4 wk were similar. The intracanal placement of calcium hydroxide weakened the fracture strength of teeth by 8.2% after 4 wk: an average of 39.23 MPa for no treatment group and 36.01 MPa for CH group. However there was no statistically significant difference between experimental groups and between time intervals. Conclusions: These results suggest that short term calcium hydroxide application is available during endodontic treatment.

• Journal of Dental Rehabilitation and Applied Science
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• v.24 no.1
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• pp.113-127
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• 2008

The purpose of this study was to evaluate effect of application of $ZirLiner^{(R)}$ and blasting treatments on shear bond strength of zirconia-veneered porcelain interface. 60 uncolored zirconia plates and 30 colored zirconia plates were fabricated and divided into nine groups of 10 according to blasting treatment such as as-ground, glass blasting and alumina blasting and zirliner application. Veneering porcelains were built up over the center of the treated zirconia ceramic surface using jig and fired according to the manufacturers' instructions. Each specimen was completely embedded in acrylic resin. The specimens were placed in a mounting jig and subjected to shear force by a universal testing machine. Load was applied at a crosshead speed of 0.5㎜/min until failure. Average shear strengths were analyzed with two-way analysis of variance and one-way analysis of variance and the Duncan's post-hoc test. The fracture surfaces of the failed specimens were examined by SEM. The obtained results were as follows: 1. Depending on surface treatment by blasting, the degree of roughness is revealed in the order of Glass-blasted, As-ground, and Alumnia-blasted. The roughness average of uncolored and colored zirconia ceramic were not significantly different from blasting treatments. 2. In uncolored zirconia ceramic, the shear bond strength were not significantly different from blasting treatments. However, the shear bond strength were significantly different from Zirliner application. 3. Used ZirLiner, mean shear bond strength of colored zirconia was lower than uncolored zirconia. Especially, mean shear bond strength of colored zirconia was quite low with alumina-blasting treatment. 4. SEM analysis showed that veneered porcelain failed in zirconia ceramic interface and there was no cohesive failure.