• The Journal of Advanced Prosthodontics
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• v.12 no.4
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• pp.181-188
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• 2020

PURPOSE. The effect of core design on the fracture resistance of zirconia-lithium disilicate (LS2) bilayered crowns for anterior teeth is evaluated by comparing with that of metal-ceramic crowns. MATERIALS AND METHODS. Forty customized titanium abutments for maxillary central incisor were prepared. Each group of 10 units was constructed using the same veneer form of designs A and B, which covered labial surface to approximately one third of the incisal and cervical palatal surface, respectively. LS2 pressed-on-zirconia (POZ) and porcelain-fused-to-metal (PFM) crowns were divided into "POZ_A," "POZ_B," "PFM_A," and "PFM_B" groups, and 6000 thermal cycles (5/55 ℃) were performed after 24 h storage in distilled water at 37 ℃. All specimens were prepared using a single type of self-adhesive resin cement. The fracture resistance was measured using a universal testing machine. Failure mode and elemental analyses of the bonding interface were performed. The data were analyzed using Welch's t-test and the Games-Howell exact test. RESULTS. The PFM_B (1376. 8 ± 93.3 N) group demonstrated significantly higher fracture strength than the PFM_A (915.8 ± 206.3 N) and POZ_B (963.8 ± 316.2 N) groups (P<.05). There was no statistically significant difference in fracture resistance between the POZ_A (1184.4 ± 319.6 N) and POZ_B groups (P>.05). Regardless of the design differences of the zirconia cores, fractures involving cores occurred in all specimens of the POZ groups. CONCLUSION. The bilayered anterior POZ crowns showed different fracture resistance and fracture pattern according to the core design compared to PFM.

• Steel and Composite Structures
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• v.35 no.4
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• pp.463-474
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• 2020

In this paper, the influence of adding multi-walled carbon nanotube (MWCNT) on the pull behavior of steel and GFRP bars in ultra-high-performance concrete (UHPC) was examined experimentally and numerically. For numerical analysis, 3D nonlinear finite element modeling (FEM) with the help of ABAQUS software was used. Mechanical properties of the specimens, including Young's modulus, tensile strength and compressive strength, were extracted from the experimental results of the tests performed on standard cube specimens and for different values of weight percent of MWCNTs. In order to consider more realistic assumptions, the bond between concrete and bar was simulated using adhesive surfaces and Cohesive Zone Model (CZM), whose parameters were obtained by calibrating the results of the finite element model with the experimental results of pullout tests. The accuracy of the results of the finite element model was proved with conducting the pullout experimental test which showed high accuracy of the proposed model. Then, the effect of different parameters such as the material of bar, the diameter of the bar, as well as the weight percent of MWCNT on the bond behavior of bar and UHPC were studied. The results suggest that modifying UHPC with MWCNT improves bond strength between concrete and bar. In MWCNT per 0.01 and 0.3 wt% of MWCNT, the maximum pullout strength of steel bar with a diameter of 16 mm increased by 52.5% and 58.7% compared to the control specimen (UHPC without nanoparticle). Also, this increase in GFRP bars with a diameter of 16 mm was 34.3% and 45%.

• Journal of the Korean Wood Science and Technology
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• v.20 no.2
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• pp.9-22
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• 1992

The aim of this research was to investigate physical and mechanical properties of various composition panels, each fabricated with a ratio of fiber to particle of 2 to 10. Type A consisted of fiber-faces and particle-core in layered-mat system. Type B consisted of fiberboard-faces on particleboard-core. Type C consisted of fibers and particles in mixed-mat system. The results obtained from tests of bending strength, internal bond, screw holding strength and stability were as follows: 1. The bending strength and internal bonding of both the Type A panel and the Type B panel were higher than those of the Type C panel and three-layered particle board. 2. The mechanical properties of the Type C panel showed the lowest values of all composition methods. It seems that the different compression ratios of the particle and fiber interrupted the densification of the fibers when hot pressed. 3. The dimensional stability of layered-mat system panels consising of fiber-faces and particle-core was better the than control particleboard. 4. In composition methods of particle and fiber, layered-composition method was more resonable than mixed-composition. The Type B panel had the highest mechanical properties of all the composition types. 5. The Type A panel was considered the ideal composition method because of its resistance to delamination between the particle-layer and the fiber-layer and because of its lower adhesive content and more effective manufa cturing process.

• Restorative Dentistry and Endodontics
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• v.37 no.1
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• pp.9-15
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• 2012

Objectives: This study evaluated the effect of 2% chlorhexidine digluconate (CHX) with different application times on microtensile bonds strength (MTBS) to dentin in class I cavities and intended to search for ideal application time for a simplified bonding protocol. Materials and Methods: Flat dentinal surfaces with class I cavities ($4mm{\times}4mm{\times}2mm$) in 40 molar teeth were bonded with etch-and-rinse adhesive system, Adper Single Bond 2 (3M ESPE) after: (1) etching only as a control group; (2) etching + CHX 5 sec + rinsing; (3) etching + CHX 15 sec + rinsing; (4) etching + CHX 30 sec + rinsing; and (5) etching + CHX 60 sec + rinsing. Resin composite was builtup with Z-250 (3M ESPE) using a bulk method and polymerized for 40 sec. For each condition, half of the specimens were immediately submitted to MTBS test and the rest of them were assigned to thermocycling of 10,000 cycles between $5^{\circ}C$ and $55^{\circ}C$ before testing. The data were analyzed using two-way ANOVA, at a significance level of 95%. Results: There was no significant difference in bond strength between CHX pretreated group and control group at the immediate testing period. After thermocycling, all groups showed reduced bond strength irrespective of the CHX use. However, groups treated with CHX maintained significantly higher MTBS than control group (p < 0.05). In addition, CHX application time did not have any significant influence on the bond strength among groups treated with CHX. Conclusion: Application of 2% CHX for a short time period (5 sec) after etching with 37% phosphoric acid may be sufficient to preserve dentin bond strength.

• Restorative Dentistry and Endodontics
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• v.33 no.3
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• pp.224-234
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• 2008

The purpose of this study was to compare the normal and two times of application time of six self-etching primers applied to enamel using microshear bond strength (uSBS) test and the finding of scanning electronic microscope (SEM). Crown of sixty human molars were bisected mesiodistally and buccal and lingual enamel of crowns were partially exposed and polished with 600 grit SiC papers. They were divided into one of two equal groups subdivided into one of six equal groups (n = 10) by self-etching primer adhesives. After the same manufacture's adhesive resin and composites were bonded on the enamel surface of each group, the bonded specimens were subjected to uSBS testing and also observed under SEM. In conclusion, generally two times of primer application time increased the enamel uSBS, especially with the statistical increase of bond strength in adhesives involving high-pH primers.

• The korean journal of orthodontics
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• v.43 no.1
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• pp.23-28
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• 2013

Objective: The purpose of this study was to evaluate the effect of casein phosphopeptide amorphous calcium phosphate (CPP-ACP) on the shear bond strength (SBS) of brackets bonded to non-demineralized teeth with either phosphoric acid etching or self-etching primer. Methods: Sixty human premolars were randomly assigned to 1 of 4 treatment groups (n = 15 each): phosphoric acid etching (group 1); self-etching primer (group 2); CPP-ACP for 2 weeks + phosphoric acid etching (group 3), and CPP-ACP for 2 weeks + self-etching primer (group 4). After bonding of the maxillary premolar metal brackets, specimens were subjected to shear forces in a testing machine. Scanning electron microscopy was used to observe etching patterns on the enamel surfaces of all teeth. A 2-way analysis of variance was used to test for effects of CPP-ACP and etching system on SBS. Results: Significantly higher mean SBSs were observed in groups subjected to phosphoric acid etching (i.e., groups 1 and 3; p < 0.05). On the other hand, SBSs did not appear to be influenced by CPP-ACP (i.e., groups 3 and 4; p > 0.05). We observed a uniform and clear etched pattern on the enamel surface of the phosphoric acid etching groups. Conclusions: CPP-ACP does not significantly affect the SBS of orthodontic brackets bonded to non-demineralized teeth, regardless of which adhesive method is used to bond the brackets.

• The Journal of Korean Academy of Prosthodontics
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• v.41 no.3
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• pp.379-386
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• 2003

Statement of problem. Resin cements are widely used in adhesive dentistry specially on all ceramic restorations. It is needed to find out adequate bonding strength between different porcelain surface treatments, commercially available porcelains, and different resin cement systems. Purpose. The purpose of this study was to evaluate shear bond strength of resin cements bonded to porcelains in three different modalities; 5 different porcelain surface treatments, 3 different resin cement systems and 3 different commercially available pressable porcelains. Material and Method. This study consisted of 3 parts. Part I examined the effect of five different surface treatments on the pressable porcelain. Fifty discs (5 mm in diameter and 3 mm in height) of Authentic porcelain were randomly divided into 5 groups (n = 10). The specimens were sanded with 320 grit SiC paper followed by 600 grit SiC paper. The specimens were treated as follow: Group 1-Sandblasting (aluminum oxide) only, Group 2 - sandblasting/ silane, Group 3 - sandblasting/ acid etching/ silane, Group 4 - acid etching only, Group 5 - acid etching/ silane. Part II examined the shear bond strength of 3 different resin cement systems (Duolink, Variolink II, Rely X ARC) on acid etching/ silane treated Authentic pressable porcelain. Part 3 examined the shear bond strength of Duolink resin cement on 3 different pressable porcelains (Authentic, Empress I, Finesse). All cemented specimens were stored in distilled water for 2 hours and tested with Ultradent shear bond strength test jig under Universal Instron machine until fracture. An analysis of variance(ANOVA) test was used to evaluate differences in shear bond strength. Result. The shear bond strength test resulted in the following: (1) Acid etched porcelains recorded greater shear bond strength values to the sandblasted porcelains. (2) Silane treated porcelains recorded greater shear bond strength values to non-silane treated porcelains. (3) There was no significant difference between sandblasting/ acid etching/ silane treated and acid etching/ silane treated porcelains. However those values were much higher than other three groups. (4) The shear bond strength with Variolink II was lower than the value of Duolink or Rely X ARC. (5) The shear bond strength of Finesse was lower than the value of Authentic or Empress I.

• The Journal of Advanced Prosthodontics
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• v.5 no.2
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• pp.98-103
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• 2013

PURPOSE. To evaluate the effects of hydrofluoric acid etching and Er,Cr:YSGG laser irradiation on the shear bond strength of resin cement to lithium disilicate ceramic. MATERIALS AND METHODS. Fifty-five ceramic blocks ($5mm{\times}5mm{\times}2mm$) were fabricated and embedded in acrylic resin. Their surfaces were finished with 1000-grit silicon carbide paper. The blocks were assigned to five groups: 1) 9.5% hydrofluoric-acid etching for 60 s; 2-4), 1.5-, 2.5-, and 6-W Er,Cr:YSGG laser applications for 60 seconds, respectively; and 5) no treatment (control). One specimen from each group was examined using scanning electron microscopy. Ceramic primer (Rely X ceramic primer) and adhesive (Adper Single Bond) were applied to the ceramic surfaces, followed by resin cement to bond the composite cylinders, and light curing. Bonded specimens were stored in distilled water at $37^{\circ}C$ for 24 hours. Shear bond strengths were determined by a universal testing machine at 1 mm/min crosshead speed. Data were analyzed using Kruskal-Wallis and Mann-Whitney U-tests (${\alpha}$=0.05). RESULTS. Adhesion was significantly stronger in Group 2 ($3.88{\pm}1.94$ MPa) and Group 3 ($3.65{\pm}1.87$ MPa) than in Control group ($1.95{\pm}1.06$ MPa), in which bonding values were lowest (P<.01). No significant difference was observed between Group 4 ($3.59{\pm}1.19$ MPa) and Control group. Shear bond strength was highest in Group 1 ($8.42{\pm}1.86$ MPa; P<.01). CONCLUSION. Er,Cr:YSGG laser irradiation at 1.5 and 2.5 W increased shear bond strengths between ceramic and resin cement compared with untreated ceramic surfaces. Irradiation at 6 W may not be an efficient ceramic surface treatment technique.

• Journal of the korean academy of Pediatric Dentistry
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• v.28 no.4
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• pp.638-642
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• 2001

Recently, plasma arc curing system for curing resin composites has been introduced. This is characterized by a high output of light energy, which has the advantage of reducing the chair time and thereby making the treatment more comportable for the patients as well as for the dentist. The purpose of this study was to compare the shear bond strengths of light-cured orthodontic adhesive polymerized with conventional halogen light and plasma arc light. The 2 curing devices used were the XL3000 (3M, USA) conventional curing light and the Flipo (LOKKI, France) plasma arc light. The results from the present study can be summarized as fellows; 1. The mean shear bond strength for three groups were quite similar for 50 second conventional light group, 2 second plasma arc curing light group, 5 second plasma arc curing light group. 2. There was no statistically significant difference for three groups(p>0.05).

• Journal of the Microelectronics and Packaging Society
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• v.17 no.1
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• pp.41-46
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• 2010

The interfacial adhesion strengths between screen-printed Ag film and epoxy resin-coated polyimide were evaluated by $180^{\circ}$ peel test method. Measured peel strength value was initially around $164.0{\pm}24.4J/m^2$, while the heat treatment during 24h at $120^{\circ}C$ increase peel strength up to $220.8{\pm}19.2J/m^2$. $85^{\circ}C/85%$ RH temperature/humidity treatment decrease peel strength to $84.1{\pm}50.8J/m^2$, which seems to be attributed to hydrolysis bonding reaction mechanism between metal and adhesive epoxy resin coating layer.