• The Journal of Advanced Prosthodontics
• /
• v.4 no.3
• /
• pp.162-169
• /
• 2012

PURPOSE. Fracture of the veneering material of zirconia restorations frequently occurs in clinical situations. The purpose of this in vitro study was to compare the fracture strengths of zirconia crowns veneered with various ceramic materials by various techniques. MATERIALS AND METHODS. A 1.2 mm, $360^{\circ}$ chamfer preparation and occlusal reduction of 2 mm were performed on a first mandibular molar, and 45 model dies were fabricated in a titanium alloy by CAD/CAM system. Forty-five zirconia copings were fabricated and divided into three groups. In the first group (LT) zirconia copings were veneered with feldspathic porcelain by the layering technique. In the second group (HT) the glass ceramic was heat-pressed on the zirconia coping, and for the third group (ST) a CAD/CAM-fabricated high-strength anatomically shaped veneering cap was sintered onto the zirconia coping. All crowns were cemented onto their titanium dies with Rely $X^{TM}$ Unicem (3M ESPE) and loaded with a universal testing machine (Instron 5583) until failure. The mean fracture values were compared by an one-way ANOVA and a multiple comparison post-hoc test (${\alpha}$= 0.05). Scanning electron microscope was used to investigate the fractured interface. RESULTS. Mean fracture load and standard deviation was $4263.8{\pm}1110.8$ N for Group LT, $5070.8{\pm}1016.4$ for Group HT and $6242.0{\pm}1759.5$ N for Group ST. The values of Group ST were significantly higher than those of the other groups. CONCLUSION. Zirconia crowns veneered with CAD/CAM generated glass ceramics by the sintering technique are superior to those veneered with feldspathic porcelain by the layering technique or veneered with glass ceramics by the heat-pressing technique in terms of fracture strength.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2006.06a
• /
• pp.286-287
• /
• 2006

Barium titanate ($BaTiO_3$) glycolate particles were synthesized at temperature as low as $100^{\circ}C$ through glycothermal reaction by using $Ba(OH)_2{\cdot}8H_2O$ and amorphous titanium hydrous gel as precursors and ethylene glycol as solvent. The particle size and morphology of $BaTiO_3$ glycolate powders can be controlled by varying the reaction conditions such as the reaction temperature and Ba:Ti molar ratio of starting precursors. After glycothermal treatment at $220^{\circ}C$ for 24 h in 1.25:1(Ba:Ti), the average particle size of the $BaTiO_3$ glycolate powder was about 200-400 nm and low agglomeration. $BaTiO_3$ powders were formed by heat-treating the glycolate powder in air at $500-1000^{\circ}C$. As a result, the size of $BaTiO_3$ crystallites changed from around 50-300 nm. It is also demonstrated that the size and shape of $BaTiO_3$ particles investigated as a function of calcination temperature. The $BaTiO_3$ particles obtained from optimum synthesis condition were pressed, sintered and measured for the dielectric property. The $BaTiO_3$ ceramics sintered at $1250^{\circ}C$ for 2 h had 98 % of theoretical density. The ceramics have an average grain size of about $1\;{\mu}m$ and displays the high dielectric constant (~3100) and low dielectric loss (<0.1) at room temperature.

• The Journal of Korean Academy of Prosthodontics
• /
• v.47 no.2
• /
• pp.191-198
• /
• 2009

Statement of problem: Ceramics have been important materials for the restoration of teeth. The demands of patients for tooth-colored restorations and the availability of various dental ceramics has driven the increased use of new types of dental ceramic materials. Improved physical properties of theses materials have expanded its use even in posterior crowns and fixed partial dentures. However, ceramic still has limitation such as low loading capability. This is critical for long-span bridge, because bridge is more subject to tensile force. Purpose: The wire reinforced ceramic was designed to increase the fracture resistance of ceramic restoration. The purpose of this study was to evaluate the fracture resistance of wire reinforced ceramic. Material and methods: Heat pressed ceramic(ingot No.200 : IPS Empress 2, Ivoclar Vivadent, Liechtenstein) and Ni-Cr wire(Alfa Aesar, Johnson Matthey Company, USA) of 0.41 mm diameter were used in this study. Five groups of twelve uniform sized ceramic specimens(width 4 mm, thickness 2 mm, length 15 mm) were fabricated. Each group had different wire arrangement. Wireless ceramic was used as control group. The experimental groups were divided according to wire number and position. One, two and three strands of wires were positioned on the longitudinal axis of specimen. In another experimental group, three strands of wires positioned on the longitudinal axis and five strands of wires positioned on the transverse axis. Three-point bending test was done with universal testing machine(Z020, Zwick, Germany) to compare the flexural modulus, flexural strength, strain at fracture and fracture toughness of each group. Fractured ceramic specimens were cross-sectioned with caborundum disc and grinded with sandpaper to observe interface between ceramic and Ni-Cr wire. The interface between ceramic and Ni-Cr wire was analyzed with scanning electron microscope(JSM-6360, JEOL, Japan) under platinum coating. Results: The results obtained were as follows: 1. The average and standard deviation in flexural modulus, flexural strength and fracture toughness showed no statistical differences between control and experimental groups. However, strain was significantly increased in wire inserted ceramics(P<.001). 2. Control group showed wedge fracture aspects across specimen, while experimental groups showed cracks across specimen. 3. Scanning electron microscopic image of cross-sectioned and longitudinally-sectioned specimens showed no gap at the interface between ceramic and Ni-Cr wire. Conclusion: The results of this study showed that wire inserted ceramics have a high strain characteristic. However, wire inserted ceramics was not enough to use at posterior area of mouth in relation to flexural modulus and flexural strength. Therefore, we need further studies.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.35 no.7
• /
• pp.779-784
• /
• 2011

This study was carried out on the crack healing of three types of SiC ceramics based on a $SiO_2$ additive, taking into account the roughness of the polishing plate used for polishing the specimens. The mixtures were subsequently hot-pressed in $N_2$ gas for one hour under 35 MPa at 2053 K. In these specimens, the optimized crack-healing condition was 1373 K for one hour in air. The crack-healing material of the cracked part was the glassy phase of $SiO_2$ that was formed by the oxidation of SiC. In the optimum healing condition, the bending strength of non-polished SiC ceramics was not completely recovered. However, the bending strength of the SAY specimen was excellent, considering the economic aspects of SAY, SAYS-1, and SAYS-2. The SAY specimen is definitely superior to the others after an hour of heat treatment. There was a decrease in the number and size of defects in the specimen polished by using a $125-{\mu}m$ polishing plate; however, the micro-surface defects were not completely repaired. The specimen polished by using a 40-${\mu}m$ polishing plate showed little voids or surface defects after an hour of heat treatment. The bending strength of the specimen mirror-polished by using a 6-${\mu}m$ polishing plate was completely recovered.

• The Journal of Korean Academy of Prosthodontics
• /
• v.36 no.5
• /
• pp.772-785
• /
• 1998

This study was undertaken to clarify the microstructure of the different IPS Empress ingots by etching and to observe the change of leucite crystal structure according to subsequent heat treatment and the crystal distribution according to sprue types(${\phi}2.8mm$, single sprue; ${\phi}1.8mm$, double sprue) by scanning electron microscopy. IPS Empress T1, O1 ingots used for staining technique, and Dentin(A2) ingots used for layering technique were selected for this study. To observe the microstructures of these ingots before pressing, the specimens were prepared in splinters($3{\times}3{\times}3mm$) taken from the original ingots. And to estimate crystal distribution and microstructural change by sprue type and subsequent heat treatment. the specimens($3{\times}3{\times}3mm$) were heat-pressed through the two types of sprues with different diameters and numbers, and all specimens were fired according to the recommended firing schedule. The observed surface was ground with waterproof papers($#800{\sim}#1800$) on the grind polisher and was cleaned ultrasonically. All specimen were etched with 0.5% hydrofluoric acid. After etching, the surface was treated by ion sputter coating for SEM observation at an accelerating voltage of 20kV. In all specimens, the central area of ground surface was observed because there was less difference in microstructure between the peripheral area and the central area. The results were as follows ; 1. In the microstructure according to the ingot type, there was a wide difference between the staining (T1,O1) and layering(Dentin A2) ingots, but there was not a considerable difference between the T1 ingot and the O1 ingot for staining technique. 2. In all specimens, the crystal dispersion of IPS Empress ceramic using double sprue was significantly more scattered than that of IPS Empress ceramic using single sprue. The degree of scattering was strongest in the Dentin(A2) specimen and weakest in the O1 ingot. 3. In the microstructural change according to the subsequent heat treatment, all of ingots had some microcracks in the inside of the leucite crystal and the glass matrix after pressing. The inner splinters of the leucite crystal became smaller, and more microcracks occurred in the glass matrix due to increasing heat treatment times. 4. The size of leucite crystals varied from $1{\mu}m\;to\;5{\mu}m$. The mean size of mature crystals was about $5{\mu}m$. The form of the crystal was similar to a circle when it was smaller and similar to an ellipse when it was larger.

• Korean Journal of Materials Research
• /
• v.2 no.5
• /
• pp.330-336
• /
• 1992

Four distinctive hot pressed and heat treated S${i_3}{N_4}$ceramics, S${i_3}{N_4}$-8%${Y_2}{O_3}$, S${i_3}{N_4}$-6% ${Y_2}{O_3}$-2% $A{l_2}{O_3}$, S${i_3}{N_4}$-4% ${Y_2}{O_3}$-3% $A{l_2}{O_3}$, 그리고 S${i_3}{N_4}$-1% MgO-1% Si$O_2$(in wt%), were prepared and characterized by X-ray diffraction, scanning electron microscopy, image analysis and mechanical tests. The fracture toughness of S${i_3}{N_4}$-8% ${Y_2}{O_3}$specimens containing large elongated grains showed the highest value of about 9.8MPa$m^{1/2}$. Two out of four S${i_3}{N_4}$, ceramics(S${i_3}{N_4}$-6% ${Y_2}{O_3}$-2% $A{l_2}{O_3}$and S${i_3}{N_4}$-4% ${Y_2}{O_3}$-3% $A{l_2}{O_3}$) heat treated at 200 $0^{\circ}C$retained the fracture strength of over 900MPa and fracture toughness of over 8.0MPa$m^{1/2}$. Large ${\beta}$-S${i_3}{N_4}$grains having a diameter larger than 1${\mu}$m appeared to contribute to increase in fracture toughness.

• The Journal of Korean Academy of Prosthodontics
• /
• v.42 no.4
• /
• pp.386-396
• /
• 2004

Statement of problem: It is not clear how to make a stable bonding between zirconia ceramic and resin cement. And the study about surface treatment of zirconia ceramic or bonding resin cement are not enough. Purpose: To measure and compare the shear bond strength of some resin cements on zirconia ceramic after different surface treatments. Material and method: 48 ceramic discs were made of 3 ceramic materials, zirconia ceramics (Zi-Ceram), heat-pressed ceramics (IPS Empress 2) and slip cast alumina ceramics (In-Ceram). According to the surface treatments of ceramic specimens and resin cements, specimens were classified into 6 groups and each group was composed of 8 specimens. For the surface treatment of Zi-Ceram group (test group), sandblasting and diamond bur preparation were applied and Superbond C&B and Panavia F were bonded respectively. For IPS Empress 2 group (control group), Variolink II was bonded after sandblasting, acid etching, silanization and for In-Ceram ALUMINA group (control group), Panavia F was bonded after sandblasting. After storing specimens in distilled water for 24 hours, the shear bond strength was measured by the universal testing machine. Results and conclusion: 1. Zi-Ceram group with Superbond C&B cement showed higher bond strength than with Panavia F cement regardless to the surface treatments (p<0.05). 2. In Zi-Ceram group with Superbond C&B cement, sandblasting treatment group (12.1MPa) showed higher bond strength than diamond bur treatment group (7.7MPa) (p<0.05). In Zi-Ceram group with Panavia F cement, there were no significant differences in the bond strength according to the surface treatments (p>0.05). 3. Zi-Ceram group with sandblasting and Superbond C&B cement (12.1MPa) showed the highest bond strength. The bond strength of this group was not significantly different from In-Ceram ALUMINA group (10.4MPa) (p>0.05) and lower than IPS Empress 2 group (15.9MPa) (p<0.05).

• Journal of Korean society of Dental Hygiene
• /
• v.14 no.4
• /
• pp.447-452
• /
• 2014

With the increase of esthetic demands, most patients want to have restorations which are not only functional but also esthetic. For the esthetic restoration, many ceramic systems have been introduced and applied in dentistry. Among those ceramic restorations, IPS e.max system composed of lithium disilicate glass ceramic is one of the most commonly used systems because it has strength and esthetic characteristics. IPS e.max system is divided into IPS e.max Press and IPS e.max CAD according to the manufacturing methods. IPS e.max Press is fabricated through heat-pressed technique with ceramic ingot, which is very simple. The restorations which are made using IPS e.max system can apply to 3 units restoration for the anterior teeth and premolar, and single posterior tooth restoration. Cementation is one of the most important clinic procedure for the longevity of the restorations. All ceramics are bonded by resin cements, it is classified into three groups including adhesive, self-adhesive, and conventional. Variolink N, which is an adhesive resin cement and manufactured by same company with IPS e.max, is recommended for the bonding of IPS e.max restoration. Conventional and self-adhesive resin cement is also available. The aim of this review article is to provide the understanding of material properties, production procedure and clinical application of IPS e.max system.

• The Journal of Advanced Prosthodontics
• /
• v.8 no.6
• /
• pp.479-488
• /
• 2016

PURPOSE. The aim of this study was to test the modulus of elasticity (E) across the interfaces of yttria stabilized zirconia (YTZP) / veneer multilayers using nanoindentation. MATERIALS AND METHODS. YTZP core material (KaVo-Everest, Germany) specimens were either coated with a liner (IPS e.max ZirLiner, Ivoclar-Vivadent) (Type-1) or left as-sintered (Type-2) and subsequently veneered with a pressable glass-ceramic (IPS e.max ZirPress, Ivoclar-Vivadent). A $5{\mu}m$ (nominal tip diameter) spherical indenter was used with a UMIS CSIRO 2000 (ASI, Canberra, Australia) nanoindenter system to test E across the exposed and polished interfaces of both specimen types. The multiple point load - partial unload method was used for E determination. All materials used were characterized using Scanning Electron Microscopy (SEM) and X - ray powder diffraction (XRD). E mappings of the areas tested were produced from the nanoindentation data. RESULTS. A significantly (P<.05) lower E value between Type-1 and Type-2 specimens at a distance of $40{\mu}m$ in the veneer material was associated with the liner. XRD and SEM characterization of the zirconia sample showed a fine grained bulk tetragonal phase. IPS e-max ZirPress and IPS e-max ZirLiner materials were characterized as amorphous. CONCLUSION. The liner between the YTZP core and the heat pressed veneer may act as a weak link in this dental multilayer due to its significantly (P<.05) lower E. The present study has shown nanoindentation using spherical indentation and the multiple point load - partial unload method to be reliable predictors of E and useful evaluation tools for layered dental ceramic interfaces.

• Restorative Dentistry and Endodontics
• /
• v.23 no.1
• /
• pp.413-423
• /
• 1998

Dental ceramics exhibit excellent esthetic property, compressive strength, chemical durability, biocompatibility and translucency. This study evaluated the shear bond strength of composite resin to the new heat-pressed ceramic material (IPS-Empress System) depending on the surface treatments and bonding agents. The surface treatments were etching with 4.0% hydrofluoric acid, application of silane, and the combination of the two methods. Composite resin was bonded to ceramic with four kinds of dentin bonding agents(All-Bond 2, Heliobond, Scotch bond Multi-purpose and Tenure bonding agents). The ceramic specimen bonded with composite resin was mounted in the testing jig, and the universal testing machine(Zwick 020, Germany) was used to measure the shear bond strength with the cross head speed of 0.5 mm/min. The results obtained were as follows 1. The mean shear bond strength of the specimens of which the ceramic surface was treated with the combination of hydrofluoric acid and silane before bonding composite resin was significantly higher than those of the other surface treatment groups(p<0.05). 2. In the case of All-Bond 2 and Scotchbond Multi-purpose bonding agent group, the surface treatment methods did not influenced significantly on the shear bond(p>0.05). 3. Of the four bonding agents tested, the shear bond strength of Heliobond was significantly lower than those of other bonding agents regardless of the surface treatment methods(p<0.05). 4. The highest shear bond strength($12.55{\pm}1.92$ MPa) was obtained with Scotchbond Multipurpose preceded by the ceramic surface treatment with the combination of 4% hydrofluoric acid and silane.