• Journal of the Korean Academy of Esthetic Dentistry
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• v.32 no.2
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• pp.46-53
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• 2023

Porcelain fractures associated with metal ceramic(MC), all ceramic (AC), and zirconia restorations are common complications. Several factors of fracture are suggested; Property of materials, Design of the coping for metal ceramic, fabrication techniques, supporting structure, occlusal force, parafunctional habit are being considered. In this article, these factors are discussed in detail.

• Journal of the Korean Ceramic Society
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• v.55 no.4
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• pp.364-367
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• 2018

The phase evolution, microstructure, and microwave dielectric properties of Sr-substituted $Ba(Mg_{0.5}W_{0.5})O_3$ ceramics, i.e., $(Ba_{1-x}Sr_x)(Mg_{0.5}W_{0.5})O_3$ ($0{\leq}x{\leq}0.30$), sintered at $1700^{\circ}C$ for 1 h were investigated. All compositions showed a 1 : 1 ordered perovskite structure. In all the compositions, $BaWO_4$ was detected as the secondary phase. With increasing x in ($Ba_{1-x}Sr_x$) $(Mg_{0.5}W_{0.5})O_3$, the lattice parameter increased linearly, indicating that a substitutional solid solution occurred. All compositions exhibited a dense microstructure. The value of ${\varepsilon}_r$ increased slightly with increasing x. The value of $Q{\times}f_0$ increased with the increase in x up to x = 0.10 and reached a saturated value of about 100,000 GHz. The composition for x = 0.20, i.e., $(Ba_{0.80}Sr_{0.20})(Mg_{0.5}W_{0.5})O_3$, sintered at $1700^{\circ}C$ for 1 h exhibited superior microwave dielectric properties of ${\varepsilon}_r=19.6$, $Q{\times}f_0=99,358GHz$, and ${\tau}_f=0.0ppm/^{\circ}C$, respectively.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.6
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• pp.349-355
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• 2017

Zinc sulphide (ZnS) nanoparticles were fabricated by hydrothermal synthesis at $180^{\circ}C$ for 12 h. Two kinds of ZnS powder (hydrothermal synthesized ZnS and commercial ZnS) were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) for phase and microstructure, respectively. The XRD patterns showed that all ZnS nanoparticles have a sphalerite (cubic) structure. The nanoparticles of two different ZnS powders were sintered by spark plasma sintering. The sintered ZnS were analyzed by XRD, SEM, and FT-IR. We found that the transmittance of the infrared region is highly dependent on the density and crystal structure of sintered ZnS and the purity of the starting ZnS powder.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.10
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• pp.601-607
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• 2016

Piezoelectric thick films of soft $Pb(Zr,Ti)O_3$ (PZT) based commercial material (S55) were fabricated using a conventional tape casting method. Ag-Pd electrodes were printed on the piezoelectric film at room temperature and all 5 layered films with a dimension of $12mm{\times}16mm$ were successfully laminated for a multi-layered piezoelectric ceramic actuator. The laminated specimens were co-fired at $1,100^{\circ}C$ for 1 h. A flat layered and dense microstructure was obtained for the $112{\mu}m$ thick piezoelectric actuator after sintering process. Thereafter, a prototype piezoelectric speaker was fabricated using the multi-layered piezoelectric ceramic actuator which can operate as a bimorph. Its SPL (sound pressure level) characteristic was also evaluated for speaker application. Frequency response revealed that the output SPL with a root mean square voltage of 10 V increased gradually to the highest peak of 87.5 dB for 1.5 kHz and exhibited a relatively stable behavior over the measured frequency range (${\leq}20kHz$) at a distance of 10 cm, implying that the fabricated piezoelectric speaker is potential for speaker applications.

• Journal of Ceramic Processing Research
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• v.19 no.5
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• pp.413-418
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• 2018

All-solid-state lithium batteries (ASSBs) using inorganic sulfide-based solid electrolytes are considered prospective alternatives to existing liquid electrolyte-based batteries owing to benefits such as non-flammability. However, it is difficult to form a favorable solid-solid interface among electrode constituents because all the constituents are solid particles. It is important to form an effective electron conduction network in composite cathode while increasing utilization of active materials and not blocking the lithium ion path, resulting in excellent cell performance. In this study, a mixture of fibrous VGCF and spherical nano-sized Super P was used to improve rate performance by fabricating valid conduction paths in composite cathodes. Then, composite cathodes of ASSBs containing 70% and 80% active materials ($LiNi_{0.6}Co_{0.2}Mn_{0.2}O_2$) were prepared by a solution-based process to achieve uniform dispersion of the electrode components in the slurry. We investigated the influence of binary carbon additives in the cathode of all-solid-state batteries to improve rate performance by constructing an effective electron conduction network.

• Journal of Korean Dental Science
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• v.8 no.1
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• pp.28-35
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• 2015

Purpose: To investigate the influence of crown margin design on the stress distribution and to localize critical sites in maxillary canine under functional loading by using three dimensional finite element analysis. Materials and Methods: The bite force of 100 N, 150 N, and 200 N was applied with an angulation of $45^{\circ}$ to the longitudinal axis of tooth. Six models were restored with IPS e.max (Ivoclar Vivadent, Schaan, Liechtenstein) with a different margin design. With lingual ledge and various thicknesses, three different core ceramics were designed in each model. Result: In the core ceramic, the maximum tensile stresses were found at the labiocervical region. In the veneering ceramic the maximum tensile stresses were found at the area where the force was applied in all models. Conclusion: Shoulder and chamfer margin types are acceptable for all-ceramic rehabilitations. A ledge on the core ceramic at cervical region may affect the strength of all-ceramic crowns.

• Journal of the Korean Ceramic Society
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• v.40 no.11
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• pp.1027-1046
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• 2003

Nanostructured materials can be engineered by the controlled assembly of several suitable nano-objects as the building blocks. While, materials properties are determined by their atomic and molecular constituents and structure, their functionalities emerge when the microstructure of these early ensembles is in the nanometer regime. The properties and functionalities of these ensembles may be different as their size grows from the nano-regime to the micron regime and bulk structures. Nanotechnology, offers a unique possibility to manipulate the properties through the fabrication of materials using the nano-objects as building blocks. Nanotechnology is therefore considered an enabling technology by which existing materials, virtually all man-made materials, can acquire novel properties and functionalities making them suitable for numerous novel applications varying from structural and functional to advanced biomedical in-vivo and in-vitro applications.

• Journal of the Korean Academy of Esthetic Dentistry
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• v.17 no.1
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• pp.23-30
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• 2008

Application of CAD/CAM is changing the way partial or full veneer all ceramic restoration is made. CAD/CAM systems, which were used mainly in other industries, have been developed and introduced for the dental purposes recently. It produced a flood of information on the CAD/CAM systems. It also influenced the development of restorative materials and all ceramic is substituting the traditional restorative materials of gold, composite resin and metal. Price increase of gold and other raw materials made the all ceramic more appealing. The introduction of a CEREC 3D system was innovative in several ways. Image of the prepared tooth is captured by camera and impression taking is unnecessary. Restoration can be delivered to the patient on one appointment and it will satisfy the demand of busy patients. One-day treatment with direct CAD/CAM system saves time compared to indirect CAD/CAM system. More superior restoration can be produced if lab work such as the adaptability check and shade selection is cooperated with lab technician. Short working time and comparably superior shade compatibility of color block was close to ideal. In the future, restorations with better quality can be fabricated in less time to busy patients thanks to the development of CAD/CAM system and dental materials.

• The Journal of Advanced Prosthodontics
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• v.8 no.2
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• pp.137-143
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• 2016

PURPOSE. Grinding with less stress on 3Y-TZP through proper selection of methods and instruments can lead to a long-term success of prosthesis. The purpose of this study was to compare the phase transformation and physical properties after zirconia surface grinding with 3 different grinding burs. MATERIALS AND METHODS. Forty disc-shaped zirconia specimens were fabricated. Each Ten specimens were ground with AllCeramic SuperMax (NTI, Kahla, Germany), Dura-Green DIA (Shofu Inc., Kyoto, Japan), and Dura-Green (Shofu Inc., Kyoto, Japan). Ten specimens were not ground and used as a control group. After the specimen grinding, XRD analysis, surface roughness test, FE-SEM imaging, and biaxial flexural strength test were performed. RESULTS. After surface grinding, small amount of monoclinic phase in all experimental groups was observed. The phase change was higher in specimens, which were ground with Dura-Green DIA and AllCeramic SuperMax burs. The roughness of surfaces increased in specimens, which were ground with Dura-Green DIA and AllCeramic SuperMax burs than control groups and ground with Dura-Green. All experimental groups showed lower flexural strength than control group, but there was no statistically significant difference between control group and ground with Dura-Green DIA and AllCeramic SuperMax burs. The specimens, which were ground with Dura-Green showed the lowest strength. CONCLUSION. The use of dedicated zirconia-specific grinding burs such as Dura-Green DIA and AllCeramic SuperMax burs decreases the grinding time and did not significantly affect the flexural strength of zirconia, and therefore, they may be recommended. However, a fine polishing process should be accompanied to reduce the surface roughness after grinding.

• The Journal of Advanced Prosthodontics
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• v.10 no.1
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• pp.65-72
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• 2018

PURPOSE. The aim of this in vitro study was to investigate the fracture resistance under chewing simulation of implant-supported posterior restorations (crowns cemented to hybrid-abutments) made of different all-ceramic materials. MATERIALS AND METHODS. Monolithic zirconia (MZr) and monolithic lithium disilicate (MLD) crowns for mandibular first molar were fabricated using computer-aided design/computer-aided manufacturing technology and then cemented to zirconia hybrid-abutments (Ti-based). Each group was divided into two subgroups (n=10): (A) control group, crowns were subjected to single load to fracture; (B) test group, crowns underwent chewing simulation using multiple loads for 1.2 million cycles at 1.2 Hz with simultaneous thermocycling between $5^{\circ}C$ and $55^{\circ}C$. Data was statistically analyzed with one-way ANOVA and a Post-Hoc test. RESULTS. All tested crowns survived chewing simulation resulting in 100% survival rate. However, wear facets were observed on all the crowns at the occlusal contact point. Fracture load of monolithic lithium disilicate crowns was statistically significantly lower than that of monolithic zirconia crowns. Also, fracture load was significantly reduced in both of the all-ceramic materials after exposure to chewing simulation and thermocycling. Crowns of all test groups exhibited cohesive fracture within the monolithic crown structure only, and no abutment fractures or screw loosening were observed. CONCLUSION. When supported by implants, monolithic zirconia restorations cemented to hybrid abutments withstand masticatory forces. Also, fatigue loading accompanied by simultaneous thermocycling significantly reduces the strength of both of the all-ceramic materials. Moreover, further research is needed to define potentials, limits, and long-term serviceability of the materials and hybrid abutments.