• The Journal of Korean Academy of Prosthodontics
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• v.45 no.1
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• pp.21-33
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• 2007

Statement of problem: The esthetic component of dental care has become increasingly more important, while new tooth-colored materials are continually marketed. Various new indirect composite materials have been developed with required advantages. The most recent development in the indirect composites has been the introduction of the second-generation laboratory composite or poly-glass materials. They are processed by different laboratory techniques based on combinations of heat, pressure, vacuum and light polymerization. Although, second generation products became available in 1995, their characteristics and clinical performance have not been adequately investigated. Purpose: The aim of this study was to measure the mechanical properties of the second generation indirect resin system and compare these with an existing universal direct composite resin. Material and method: In this study four indirect composite material (Adoro LC, BelleGlass HP, Tescera, Synfony) were tested for flexural strength, wear resistance, hardness and their degree of conversion against Z250, a light cure direct composite. Results: Within the limitations of this study, the following conclusions were drawn: 1. From the abrasion wear result, Adoro showed the least volume loss while Synfony showed the greatest volume loss. Z250 and BelleGlass HP didn't show significant difference (p>0.05), but they showed significant difference with other groups (p<0.05). From the attrition wear, BelleGlass HP showed the least volume loss and it didn’t show significant difference with Tescera (p>0.05). While Synfony showed the greatest volume loss that it showed significant difference with other groups (p>0.05). 2. Mean values of flexural strength by means of three point bending test was in the order of Z250, Adoro, Belleglass HP, Tescera and Synfony. Mean elastic modulus was in the order of Z250, BelleGlass HP, Tescera, Adoro and Synfony. 3. The result of Vicker‘s microhardness value showed that significantly higher value in Z250 (p<0.05), and is in the order of BelleGlass HP, Tescera, Adoro and Synfony. 4. The degree of conversion measured by FT-IR showed significantly higher value in BelleGlass HP (p<0.05), and is in the order of Adoro, Synfony, Tescera and Z250. Conclusion: Significant differences were found in the flexural strength, wear resistance, hardness and their degree of conversion.

• Journal of dental hygiene science
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• v.10 no.6
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• pp.445-450
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• 2010

The aim of this study was to evaluate the effect according to the fiber type and combination on the reinforcement of heat-polymerized denture base resin. The heat-polymerized resin(Vertex RS, Dentimax, Netherlands) was used in this study. Glass fiber(GL; ER 270FW, Hankuk Fiber Glass, Korea), polyaromatic polyamide fiber(PA; aramid; Kevlar-49, Dupont, U.S.A.) and ultra high molecular weight polyethylene fiber(PE, polyethylene; P.E, Dong Yang Rope, Korea) were used to reinforce the denture base resin specimens. The final size of test specimen was $64mm{\times}10mm{\times}3.3mm$. The specimens of each group were stored in distilled water at $37^{\circ}C$ for 50 hours before measurement. The flexural strength and flexural modulus were measured by an universal testing machine(Z020, Zwick, Germany) at a crosshead speed of 5 mm/min in a three-point bending mode. In this study, all fibers showed reinforcing effects on denture base resin(p<0.05). In terms of flexural strength and flexural modulus, glass fiber 5.3 vol.% showed most effective reinforcing effect on heat polymerized denture base resin. For flexural modulus, PA/GL was the highest in denture base resin specimen for hybrid FRC using two combination (p<0.05). Glass fiber 5.3 vol.% and PA/GL are considered to be applied effectively in reinforcing the heat polymerized denture base resin.

• The Journal of Advanced Prosthodontics
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• v.13 no.4
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• pp.226-236
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• 2021

PURPOSE. This study aimed to evaluate the effect of incorporating zirconium oxide nanoparticles (nano-ZrO₂) in polymethylmethacrylate (PMMA) denture base resin on flexural properties at different material thicknesses. MATERIALS AND METHODS. Heat polymerized acrylic resin specimens (N = 120) were fabricated and divided into 4 groups according to denture base thickness (2.5 mm, 2.0 mm, 1.5 mm, 1.0 mm). Each group was subdivided into 3 subgroups (n = 10) according to nano-ZrO₂ concentration (0%, 2.5%, and 5%). Flexural strength and elastic modulus were evaluated using a three-point bending test. One-way ANOVA, Tukey's post hoc, and two-way ANOVA were used for data analysis (α = .05). Scanning electron microscopy (SEM) was used for fracture surface analysis and nanoparticles distributions. RESULTS. Groups with 0% nano-ZrO₂ showed no significant difference in the flexural strength as thickness decreased (P = .153). The addition of nano-zirconia significantly increased the flexural strength (P < .001). The highest value was with 5% nano-ZrO₂ and 2 mm-thickness (125.4 ± 18.3 MPa), followed by 5% nano-ZrO₂ and 1.5 mm-thickness (110.3 ± 8.5 MPa). Moreover, the effect of various concentration levels on elastic modulus was statistically significant for 2 mm thickness (P = .001), but the combined effect of thickness and concentration on elastic modulus was insignificant (P = .10). CONCLUSION. Reinforcement of denture base material with nano-ZrO₂ significantly increased flexural strength and modulus of elasticity. Reducing material thickness did not decrease flexural strength when nano-ZrO₂ was incorporated. In clinical practice, when low thickness of denture base material is indicated, PMMA/nano-ZrO₂ could be used with minimum acceptable thickness of 1.5 mm.

• The korean journal of orthodontics
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• v.33 no.2 s.97
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• pp.121-130
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• 2003

The purpose of this study was to evaluate the possibile clinical application of electroplating to increase diameter of an orthodontic wire, through examining the change of physical properties. The diameter of stainless steel orthodontic wire was increased from 0.016 inch to 0.018 inch by electroplating in a bath of nickel sulfate 100g/L, nickel chloride 60g/L, boric acid 30g/L, and sodium chloride 50g/L, under the conditions of 1.7V, $25\~29^{\circ}C\;and\;3.1\~3.3pH$. During the electroplating, the rate of diameter increase was measured every minute. To investigate uniformity, the diameter was measured at three different locations of each wire specimen aster electroplating. An X-ray diffraction test was performed to analyze the nature of the electroplated metal. Following heat treatment to improve adhesion between the wire and electroplated metal, a three-point bending test was conducted to compare stiffness, field strength, and ultimate strength among four wire groups; 0.016 inch, electroplated 016, electroplated and heat-treated 016, and 0.018 inch wires. Through the comparison of each wire group, following results were obtained. 1. In the load-deflection graph, the curve of the electroplated group was Placed between that of the 0.016 inch group and the 0.018 inch group, and the owe was closer to the 0.018 inch group by heat treatment. 2. In the electroplated and heat-treated 016 wire group, the values of stiffness, yield strength and ultimate strength showed higher tendency than in the original 0.016 Inch group. Stiffness and ultimate strength showed statistically significant differences between two groups. 3. Stiffness, yield strength, and ultimate strength of electroplated wire presented lower values than those of 0.018 inch wire group. 4. Stiffness, yield strength, and ultimate strength of electroplated and heat-treated wire showed higher tendency than those of electroplated wire group, and ultimate strength showed statistically significant difference between two groups. 5. After electroplating, the difference in diameter between the three locations was within $0.1\~0.3\%$ variation, and showed no statistical significance.

• 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.

• Tunnel and Underground Space
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• v.30 no.3
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• pp.256-269
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• 2020

The objective of this study is to evaluate the stress thresholds in crack development and the corrected fracture toughness of KURT granite under dry and saturated conditions. The stress thresholds were identified by calculation of inelastic volumetric strain from an uniaxial compression test. The corrected fracture toughness was estimated by using the Level II method (Chevron Bend specimen), suggested by ISRM (1988), in which non-linear behaviors of rock was taken into account. Average crack initiation stress(σ_ci) and crack damage stress(σ_cd) under a dry condition were 91.1 MPa and 128.7 MPa. While, average crack initiation stress(σ_ci) and crack damage stress(σ_cd) under a saturated condition were 58.2 MPa and 68.2 MPa. The crack initiation stress and crack damage stress of saturated ones decreased 36% and 47% respectively compared to those of dry specimens. A decrease in crack damage stress is relatively larger than that of crack initiation stress under a saturated condition. This indicates that the unstable crack growth can be more easily generated because of the saturation effect of water compared to the dry condition. The average corrected fracture toughness of KURT granite was 0.811 MPa·m^0.5. While, the fracture toughness of saturated KURT granite(K_CB) was 0.620 MPa·m^0.5. The corrected fracture toughness of rock in saturated condition decreases by 23.5% compared to that in dry condition. It is found that the resistance to crack propagation decreases under the saturated geological condition.