• The Journal of Korean Academy of Prosthodontics
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• v.40 no.6
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• pp.572-576
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• 2002

This investigation was designed to estimate the biaxial flexure strength and fracture toughness of lithium disilicate glass-ceramics of IPS Empress 2 system pressed with as-received ingots and their sprue buttons. Two groups of the lithium disilicate glass-ceramics were prepared as follows: group 1 is ingot-pressed group; group 2 is sprue button-pressed group. A ball-on-three-ball test was used to determine biaxial flexure strength (BFS) of disks in wet environment. Scanning electron microscopy(SEM) analysis was conducted to observe the microstructure of the ceramics. Unpaired t-test showed that there were no differences in the mean biaxial Hem strength (BFS) and KIC values between group 1 and 2 (p > 0.05). Two groups showed similar values in the KIC and the strength at 5% failure probability. The SEM micrographs of the IPS Empress 2 glass-ceramic showed a closely packed, multi-directionally interlocking pattern of numerous lithium disilicate crystals protruding from the glass matrix. The lithium orthophosphate crystals could not be observed on the fracture surface etched. There was no a marked difference of the microstructure between group 1 and 2. Although there were no tests including color stability, casting accuracy, etc., the results of this study implied that we could reuse the sprue button of the pressed lithium disilicate glass-ceramic of IPS Empress 2 system.

• Journal of Dental Rehabilitation and Applied Science
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• v.29 no.4
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• pp.359-365
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• 2013

The aim of this study was to evaluate the effect of temporary restorative and filling material on bonding strength between lithium disilicate glass-ceramic and dentin. 60 extracted human molars were cross-sectioned at occlusal third and were embedded into self-cure acrylic resin. Then the teeth were randomly divided into four groups of 15 each. Lithium disilicate glass-ceramic is cemented to dentin as follows: after no any application of the provisional materials (Group A), after application of ALIKETM (GC America Inc.)(Group B), after application of Luxatemp$^{(R)}$ Automix plus (DMG, Germany)(Group C), after application of Fermit$^{(R)}$ (Ivoclar Vivadent, Leichtenstein)(Group D). After the specimens were stored in distilled water for 24 hours, the shear bond strength of the specimens were measured using UTM (Zwick 1456 41, Zwick, Germany) at a crosshead speed of 1mm/min. The data were analysed by one-way ANOVA and Tukey HSD tests. There were no statistically significant differences of bond strength among the groups. Fracture type was showed mixed type of adhesive and cohesive fracture in most of specimens. Within the limitation of this study, bond strength of adhesive resin cement between lithium disilicate glass-ceramic and dentin was not affected by provisional restorative and filling materials.

• Journal of the Korean Ceramic Society
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• v.48 no.4
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• pp.269-277
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• 2011

Glass-ceramics based on lithium disilicate($Li_2Si_2O_5$) are prepared by heat-treatment of glasses in a system of $SiO_2-Li_2O-K_2O-Al_2O_3$ with different compositions. The crystallization heat-treatment was conducted at the temperature range of $700{\sim}900^{\circ}C$ and samples were analyzed by XRD and SEM. Mechanical properties were determined by a Vicker's hardness and 4 point bending strength. When $SiO_2/Li_2O$ ratio increased, cristobalite and tridymite crystals showed more predominate than lithium disilicate crystals. Increase in $Al_2O_3$ contents in the glass suppressed crystallzation of lithium disilicate crystals. Increase in ZnO, $B_2O_3$ contents in the glass decreased crystallization temperature of lithium disilicate crystals, and increased mechanical properties because of the reduction of the lithium disilicate crystal size.

• The Journal of Advanced Prosthodontics
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• v.8 no.1
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• pp.43-52
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• 2016

PURPOSE. This study was conducted to evaluate the effects of full-coverage all-ceramic zirconia, lithium disilicate glass-ceramic, leucite glass-ceramic, or stainless steel crowns on antagonistic primary tooth wear. MATERIALS AND METHODS. There were four study groups: the stainless steel (Steel) group, the leucite glass-ceramic (Leucite) group, the lithium disilicate glass-ceramic (Lithium) group, and the monolithic zirconia (Zirconia) group. Ten flat crown specimens were prepared per group; opposing teeth were prepared using primary canines. A wear test was conducted over 100,000 chewing cycles using a dual-axis chewing simulator and a 50 N masticating force, and wear losses of antagonistic teeth and restorative materials were calculated using a three-dimensional profiling system and an electronic scale, respectively. Statistical significance was determined using One-way ANOVA and Tukey's test (P<.05). RESULTS. The Leucite group ($2.670{\pm}1.471mm^3$) showed the greatest amount of antagonist tooth wear, followed by in decreasing order by the Lithium ($2.042{\pm}0.696mm^3$), Zirconia ($1.426{\pm}0.477mm^3$), and Steel groups ($0.397{\pm}0.192mm^3$). Mean volume losses in the Leucite and Lithium groups were significantly greater than in the Steel group (P<.05). No significant difference was observed between mean volume losses in the Zirconia and Steel groups (P>.05). CONCLUSION. Leucite glass-ceramic and lithium disilicate glass-ceramic cause more primary tooth wear than stainless steel or zirconia.

• The Journal of Advanced Prosthodontics
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• v.7 no.4
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• pp.271-277
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• 2015

PURPOSE. This study was to evaluate the marginal fit of two CAD-CAM anatomic contour zirconia crown systems compared to lithium disilicate glass-ceramic crowns. MATERIALS AND METHODS. Shoulder and deep chamfer margin were formed on each acrylic resin tooth model of a maxillary first premolar. Two CAD-CAM systems (Prettau$^{(R)}$Zirconia and ZENOSTAR$^{(R)}$ZR translucent) and lithium disilicate glass ceramic (IPS e.max$^{(R)}$press) crowns were made (n=16). Each crown was bonded to stone dies with resin cement (Rely X Unicem). Marginal gap and absolute marginal discrepancy of crowns were measured using a light microscope equipped with a digital camera (Leica DFC295) magnified by a factor of 100. Two-way analysis of variance (ANOVA) and post-hoc Tukey's HSD test were conducted to analyze the significance of crown marginal fit regarding the finish line configuration and the fabrication system. RESULTS. The mean marginal gap of lithium disilicate glass ceramic crowns (IPS e.max$^{(R)}$press) was significantly lower than that of the CAD-CAM anatomic contour zirconia crown system (Prettau$^{(R)}$Zirconia) (P<.05). Both fabrication systems and finish line configurations significantly influenced the absolute marginal discrepancy (P<.05). CONCLUSION. The lithium disilicate glass ceramic crown (IPS e.max$^{(R)}$press) had significantly smaller marginal gap than the CAD-CAM anatomic contour zirconia crown system (Prettau$^{(R)}$Zirconia). In terms of absolute marginal discrepancy, the CAD-CAM anatomic contour zirconia crown system (ZENOSTAR$^{(R)}$ZR translucent) had under-extended margin, whereas the CAD-CAM anatomic contour zirconia crown system (Prettau$^{(R)}$Zirconia) and lithium disilicate glass ceramic crowns (IPS e.max$^{(R)}$press) had overextended margins.

• Journal of Technologic Dentistry
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• v.40 no.1
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• pp.9-15
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• 2018

Purpose: The purpose of this study is to investigate the effect of lithium disilicate glass ceramic polishing on the strength of the final prosthesis. Methods: Fourteen lithium disilicate glass ceramic specimens were prepared. These were randomly divided into two groups of seven(LPG: low polishing group, HPG: high polishing group). In LPG, SiC paper was sequentially polished using 300, 600, 800, 1000 grit, and the specifications of the test piece were adjusted. HPG was sequentially polished using 300, 600, 800, 1000, 1200, 1500, and 2000 grit. Two groups of specimens are executed 3- point bending test. Using the statistical program SPSS 22.0, the average values of the strengths of the two groups were compared in the Mann-Whiteney test. The significance level was set at 0.05. Results: The mean strength value of HPG was measured at $307.14{\pm}23.28MPa$ significantly higher than LPG(p<0.001). Conclusion : The final polishing of the prosthesis is aesthetically important but has proven to play an important role in the flexural strength, early fracture, and prolongation of the prosthesis.

• Restorative Dentistry and Endodontics
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• v.42 no.1
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• pp.1-8
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• 2017

Objectives: The purpose of this study was to evaluate the effect of adhesive luting on the fracture resistance of zirconia compared to that of a composite resin and a lithium disilicate glass ceramic. Materials and Methods: The specimens (dimension: $2mm{\times}2mm{\times}25mm$) of the composite resin, lithium disilicate glass ceramic, and yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) were prepared. These were then divided into nine groups: three non-luting groups, three non-adhesive luting groups, and three adhesive luting groups, for each restorative material. In the non-luting groups, specimens were placed on the bovine tooth without any luting agents. In the non-adhesive luting groups, only zinc phosphate cement was used for luting the specimen to the bovine tooth. In the adhesive luting groups, specimens were pretreated, and the adhesive luting procedure was performed using a self-adhesive resin cement. For all the groups, a flexural test was performed using universal testing machine, in which the fracture resistance was measured by recording the force at which the specimen was fractured. Results: The fracture resistance after adhesive luting increased by approximately 29% in the case of the composite resin, 26% in the case of the lithium disilicate glass ceramic, and only 2% in the case of Y-TZP as compared to non-adhesive luting. Conclusions: The fracture resistance of Y-TZP did not increased significantly after adhesive luting as compared to that of the composite resin and the lithium disilicate glass ceramic.

• The Journal of Korean Academy of Prosthodontics
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• v.38 no.5
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• pp.575-582
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• 2000

This investigation was designed to determine whether heat-pressing and/or simulated heat treatments affected the flexure strength and the microstructure of the lithium disilicate glass-ceramic in the IPS Empress 2 system. Four groups of the specimens were prepared as follows: group 1 - as-received material, group 2 - heat-pressed material; group 3 - heat-pressed and simulated initial heat-treated material; group 4 - heat-pressed and the simulated heat-treated material with full firings for a final restoration. The three-point bending test and the scanning elec-tron microscope (SEM) analysis was conducted for the purpose of this study. The flexure strength of group 2 was significantly higher than that of group 1. However, there were no significant differences in strength among group 2, 3, and 4, and between group 1 and 4. The SEM micrographs of the lithium disilicate glass-ceramic showed the closely packed, multi-directionally interlocking microstructure of numerous lithium disilicate crystals protruding from the glass matrix. The crystals of the heat-pressed materials (group 2, 3, and 4) were a little denser and about two times bigger than those of the as-received material (group 1). This change of microstructure is more obviously exhibited particularly between group 1 and 2. However, there was no a marked difference among group 2, 3, and 4 after the heat-pressing procedure. Although there were significant increase of the strength and some changes of the microstructure after the heat-pressing operation, the combination of the heat-pressing and the simulated subsequent heat treatments did not produce the increase of strength of IPS Empress 2 glass-ceramic.

• Journal of Technologic Dentistry
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• v.43 no.4
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• pp.175-180
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• 2021

Purpose: This study investigates the effect of repeated use of lithium disilicate glass-ceramics on color stability. Methods: In this study, 2 types of lithium disilicate glass-ceramics were used and they were divided into 4 groups after 1st, 2nd, 3rd, and 4th heat pressing. The L^*, a^*, and b^* values of all specimens were measured using the VITA Easyshade Advance 4.0. These values was used to determine the ∆E value and transparency. IBM SPSS Statistics ver. 24.0, a statistical significance level of 0.05 and one-way ANOVA were used for all data. Results: In all groups, the L^* and b^* values were the lowest in the specimens subjected to the 4th heat pressing and the corresponding a^* value was the highest. All specimens showed ∆E values of ≤3.3, indicating color changes that were not visible with the naked eye, and the color difference increased with the number of repeated heat pressing. The transparency of all specimens decreased as the number of repeated uses increased. Conclusion: According to the number of repeated heat pressing, the color difference of Rosetta SP (HASSBIO) was larger than that of IPS e.max Press (Ivoclar Vivadent), but it was clinically acceptable in all groups. Moreover, transparency decreased as the number of heat presses increased in all groups. According to the above findings, the lithium disilicate glass-ceramic has high color stability due to repeated heat pressing, implying that it can be used in clinical settings regularly.

• Journal of the Korean Ceramic Society
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• v.41 no.2
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• pp.143-150
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• 2004

Biaxial flexure strength (ball-on-3-ball) and fracture toughness (indentation microfracture) of heat-pressable glass-ceramics for dental use were investigated in this study. Crystal phase and microstructure of glass-ceramics were analyzed by XRD. SEM, and TEM. Crack propagation in specimens was not effectively arrested by dispersed crystalline particles. However, higher degree of crystallization probably contributes to strengthening of glass-ceramics. Better clinical reliability can be expected from lithium disilicate glass-ceramic because of its significantly higher biaxial flexure strength and fracture toughness.