• Journal of Technologic Dentistry
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• v.31 no.2
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• pp.39-44
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• 2009

In the orthopedic field which firstly used zirconia as artificial joints, researchers had studied the reasons for collapsing zirconia used as restorative material by accumulated inner cracks in several years and they found out Low Temperature Degradation is one of the reasons. In the dentistry field, it has not been too long since they used zirconia as the cores of all-ceramic restoration; however, the study is needed as prophylactic measure against Low Temperature Degradation which can be caused by saliva wetting the mouth all the time and frictional forces such as bite pressure and masticatory pressure. Artificial aging by autoclaving is used because there are difficulties of testing in the patient's mouth. To study the changes in the material properties, the flexural strength of dental zirconia ceramic is measured before and after the test. The following are the result of the test. 1) The zirconia blocks in the autoclaves at $130^{\circ}C$ and $200^{\circ}C$ are phase-shifted tetragonal to monoclinic by Low Temperature Degradation. 2)The non-autoclaved specimens have the average fractural strength of 1346.4MPa, the specimens autoclaved at $130^{\circ}C$ have 1226.4Mpa and the specimens autoclaved at $200^{\circ}C$ have 1024.1MPa. The tests show that as the temperature increases, the flexural strength tend to decrease and the differences are noticeable(p<0.001). 3)Through the Duncan's post-hoc test, the differences in flexural strength of the 3 groups were listed in order of strength like normal temperature>at $130^{\circ}C$ autoclave low temperature degradation> at $200^{\circ}C$ autoclave low temperature degradation.

• The Journal of Advanced Prosthodontics
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• v.6 no.6
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• pp.444-450
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• 2014

PURPOSE. To compare the accuracy of marginal and internal adaptation of zirconia (Zr) copings fabricated on anatomic (A), semi-anatomic (SA) and non-anatomic (NA) occlusal surface preparations. MATERIALS AND METHODS. 45 extracted bicuspid teeth were prepared for receiving zirconia crowns, with different occlusal preparation designs A=15, SA=15 & NA=15. The Zr copings were fabricated by using CAD4DENT, CAD/CAM. The copings were adjusted, cemented and were cross sectioned centrally from buccal cusp tip to lingual cusp tip into mesial and distal halves. The copings were examined under electron microscope at ${\times}200$ magnification and the measurements were recorded at 9 predetermined areas in micrometers. RESULTS. Overall mean gap values for the three groups was found to be $155.93{\pm}33.98{\mu}m$ with Anatomical Occlusal preparation design having the least gap value of $139.23{\pm}30.85{\mu}m$ showing the best adaptation among the groups. Post Hoc Tukey's test showed a statistically significant difference (P=.007) between the means of gap for A & NA preparation designs. Measurements recorded at 9 predetermined points showed variations for the three groups. CONCLUSION. Anatomical occlusal preparation designs resulted in better marginal and internal adaptation of Zr copings. There is a considerable variation between the measured marginal and internal gap values for the Zr copings fabricated by the (CAD4DENT-CAD/CAM). This variation may be associated with the lack of standardization of the preparation of teeth, computerized designing of the coping for each tooth, cement used, uniform pressure application during the cementation of the copings, sectioning of the copings and the microscopic measurements.

• Journal of Technologic Dentistry
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• v.38 no.3
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• pp.157-163
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• 2016

Purpose: It is to compare and evaluate the change of the wear rate and phase variation of the Zirconia before and after the sintering after the grinding by a high speed equipment manufactured for the Zirconia. Methods: The specimen of the sintered Zirconia was manufactured as size of $15mm{\times}15mm{\times}2mm$. The grinding has been applied to each of all pieces of each test groups for a minute fit for each condition at same speed of 50,000 rpm by a diamond bur at high speed handpiece with injection of the air and water. For the observation of the surface before and after the sintering of the each test piece, the cross section of it was observed as 100 magnification by a scanning electron microscope after it was coated by PT, and the diffraction analysis was performed by XDR to compare the crystal phase of the Zirconia. The average surface roughness value of all specimens were evaluated. The wear test was performed at room temperature by applying a load of 1kg for 120,000 cycles for the chewing period 6 months. Wear was analyzed for the enamel cusps by measurement of the vertical substance loss with a laser scanner. Conclusion: The phase variation from the tetragonal phase to the monoclinic phase was confirmed in the test group of the pre-sintered Zirconia after the grinding, and the value of the surface roughness and the wear rate was increased in experimental group.

• Korean Journal of Materials Research
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• v.34 no.2
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• pp.79-84
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• 2024

Thin films of yttria-stabilized zirconia (YSZ) nanoparticles were prepared using a low-temperature deposition and crystallization process involving successive ionic layer adsorption and reaction (SILAR) or SILAR-Air spray Plus (SILAR-A+) methods, coupled with hydrothermal (175 ℃) and furnace (500 ℃) post-annealing. The annealed YSZ films resulted in crystalline products, and their phases of monoclinic, tetragonal, and cubic were categorized through X-ray diffraction analysis. The morphologies of the as-prepared films, fabricated by SILAR and SILAR-A+ processes, including hydrothermal dehydration and annealing, were characterized by the degree of surface cracking using scanning electron microscopy images. Additionally, the thicknesses of the YSZ thin films were compared by removing diffusion layers such as spectator anions and water accumulated during the air spray plus process. Crack-free YSZ thin films were successfully fabricated on glass substrates using the SILAR-A+ method, followed by hydrothermal and furnace annealing, making them suitable for application in solid oxide fuel cells.

• Journal of Dental Rehabilitation and Applied Science
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• v.24 no.1
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• pp.113-127
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• 2008

The purpose of this study was to evaluate effect of application of $ZirLiner^{(R)}$ and blasting treatments on shear bond strength of zirconia-veneered porcelain interface. 60 uncolored zirconia plates and 30 colored zirconia plates were fabricated and divided into nine groups of 10 according to blasting treatment such as as-ground, glass blasting and alumina blasting and zirliner application. Veneering porcelains were built up over the center of the treated zirconia ceramic surface using jig and fired according to the manufacturers' instructions. Each specimen was completely embedded in acrylic resin. The specimens were placed in a mounting jig and subjected to shear force by a universal testing machine. Load was applied at a crosshead speed of 0.5㎜/min until failure. Average shear strengths were analyzed with two-way analysis of variance and one-way analysis of variance and the Duncan's post-hoc test. The fracture surfaces of the failed specimens were examined by SEM. The obtained results were as follows: 1. Depending on surface treatment by blasting, the degree of roughness is revealed in the order of Glass-blasted, As-ground, and Alumnia-blasted. The roughness average of uncolored and colored zirconia ceramic were not significantly different from blasting treatments. 2. In uncolored zirconia ceramic, the shear bond strength were not significantly different from blasting treatments. However, the shear bond strength were significantly different from Zirliner application. 3. Used ZirLiner, mean shear bond strength of colored zirconia was lower than uncolored zirconia. Especially, mean shear bond strength of colored zirconia was quite low with alumina-blasting treatment. 4. SEM analysis showed that veneered porcelain failed in zirconia ceramic interface and there was no cohesive failure.

• 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.

• The Journal of Advanced Prosthodontics
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• v.12 no.5
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• pp.283-290
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• 2020

PURPOSE. The present study aimed to evaluate the clinical applicability of monolithic zirconia (MZ) crowns of different thickness via determination of fracture resistance and marginal fit. MATERIALS AND METHODS. MZ crowns with 0.5, 0.8, 1.0, and 1.5 mm thickness and porcelain fused to metal (PFM) crowns were prepared, ten crowns in each group. Marginal gaps of the crowns were measured. All crowns were aged with thermal cycling (5 - 55℃/10000 cycle) and chewing simulator (50 N/1 Hz/lateral movement: 2 mm, mouth opening: 2 mm/240000 cycles). After aging, fracture resistance of crowns was determined. Statistical analysis was performed with one-way ANOVA and Tukey's HDS post hoc test. RESULTS. Fracture loads were higher in the PFM and 1 mm MZ crowns compared to 0.5 mm and 0.8 mm crowns. 1.5 mm MZ crowns were not broken even with the highest force applied (10 kN). All marginal gap values were below 86 ㎛ even in the PFM crowns, and PFM crowns had a higher marginal gap than the MZ crowns. CONCLUSION. The monolithic zirconia exhibited high fracture resistance and good marginal fit even with the 0.5 mm thickness, which might be used with reduced occlusal thickness and be beneficial in challengingly narrow interocclusal space.

• Journal of the Korean Society for Heat Treatment
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• v.37 no.1
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• pp.1-8
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• 2024

Phase stability of tetragonal crystals in yttria-stabilized zirconia ceramics is dependent on the content of yttria and the heat-treatment condition, related with mechanical properties. In this study, we fabricated the 1.5 mol% yttria-stabilized zirconia (1.5Y-YSZ) ceramics by cold isostatic pressing (CIP) and post-sintering at temperature range of 1200 to 1350℃ for 2 hours and investigated the sintered properties and microstructural evolution. Sintered and microstructural parameters, i.e, apparent density, grain size and phase composition of 1.5Y-YSZ ceramics were mainly dependent on the sintering temperature. Maximum sintered density of 99.4 % and average grain size of 200-300 nm could be obtained from the heat-treatment condition above sintering temperature at 1300℃ for 2 hours, possessing the superior mechanical hardness with 1200 Hv. However, phase stability of tetragonal grains in 1.5 YSZ ceramics is very low, inducing the phase transformation to monoclinic crystals on specimen surface during cooling after heat-treatment.

• The Journal of Advanced Prosthodontics
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• v.7 no.3
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• pp.233-239
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• 2015

PURPOSE. This study aimed to evaluate the fit of zirconia ceramics before and after veneering, using 3 different veneering processes (layering, press-over, and CAD-on techniques). MATERIALS AND METHODS. Thirty standardized zirconia CAD/CAM frameworks were constructed and divided into three groups of 10 each. The first group was veneered using the traditional layering technique. Press-over and CAD-on techniques were used to veneer second and third groups. The marginal gap of specimens was measured before and after veneering process at 18 sites on the master die using a digital microscope. Paired t-test was used to evaluate mean marginal gap changes. One-way ANOVA and post hoc tests were also employed for comparison among 3 groups (${\alpha}$=.05). RESULTS. Marginal gap of 3 groups was increased after porcelain veneering. The mean marginal gap values after veneering in the layering group ($63.06{\mu}m$) was higher than press-over ($50.64{\mu}m$) and CAD-on ($51.50{\mu}m$) veneered groups (P<.001). CONCLUSION. Three veneering methods altered the marginal fit of zirconia copings. Conventional layering technique increased the marginal gap of zirconia framework more than pressing and CADon techniques. All ceramic crowns made through three different veneering methods revealed clinically acceptable marginal fit.

• The Journal of Advanced Prosthodontics
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• v.3 no.3
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• pp.119-125
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• 2011

PURPOSE. The aim of this study was to evaluate the influence of resin cement thickness on the microtensile bond strength between zirconium-oxide ceramic and resin cement. MATERIALS AND METHODS. Thirty-two freshly extracted molars were transversely sectioned at the deep dentin level and bonded to air-abraded zirconium oxide ceramic disks. The specimens were divided into 8 groups based on the experimental conditions (cement type: Rely X UniCem or Panavia F 2.0, cement thickness: 40 or 160 ${\mu}m$, storage: thermocycled or not). They were cut into microbeams and stored in $37^{\circ}C$ distilled water for 24 h. Microbeams of non-thermocycled specimens were submitted to a microtensile test, whereas those of thermocycled groups were thermally cycled for 18,000 times immediately before the microtensile test. Three-way ANOVA and Sheffe's post hoc tests were used for statistical analysis (${\alpha}$=95%). RESULTS. All failures occurred at the resin-zirconia interface. Thermocycled groups showed lower microtensile bond strength than non-thermocycled groups (P<.001). Differences in cement thickness did not influence the resin-zirconia microtensile bond strength given the same resin cement or storage conditions (P>.05). The number of adhesive failures increased after thermocycling in all experimental conditions. No cohesive failure was observed in any experimental group. CONCLUSION. When resin cements of adhesive monomers are applied over air-abraded zirconia restorations, the degree of fit does not influence the resin-zirconia microtensile bond strength.