• The Journal of Advanced Prosthodontics
• /
• v.9 no.5
• /
• pp.394-401
• /
• 2017

PURPOSE. The purpose of this study was to compare the optical properties of pre-colored dental monolithic zirconia ceramics of various thicknesses sintered in a microwave and those in a conventional furnace. MATERIALS AND METHODS. A2-shade of pre-colored monolithic zirconia ceramic specimens ($22.0mm{\times}22.0mm$) in 3 thickness groups of 0.5, 1.0, and 1.5 mm were divided into 2 subgroups according to the sintering methods (n=9): microwave and conventional sintering. A spectrophotometer was used to obtain CIELab color coordinates, and translucency parameters and CIEDE2000 color differences (${\Delta}E_{00}$) were measured. The relative amount of monoclinic phase ($X_m$) was estimated with x-ray diffraction. The surface topography was analyzed by atomic force microscope and scanning electron microscope. Statistical analyses were conducted with two-way ANOVA (${\alpha}=.05$). RESULTS. There were small interaction effects on CIE $L^*$, $a^*$, and TP between sintering method and thickness (P<.001): $L^*$ (partial eta squared ${{\eta}_p}^2=0.115$), $a^*$ (${{\eta}_p}^2=0.136$), and TP (${{\eta}_p}^2=0.206$), although higher $b^*$ values were noted for microwave sintering regardless of thickness. Color differences between two sintering methods ranged from 0.52 to 0.96 ${\Delta}E_{00}$ units. The $X_m$ values ranged from 7.03% to 9.89% for conventional sintering, and from 7.31% to 9.17% for microwave sintering. The microwave-sintered specimen demonstrated a smoother surface and a more uniform grain structure compared to the conventionally-sintered specimen. CONCLUSION. With reduced processing time, microwave-sintered pre-colored dental monolithic zirconia ceramics can exhibit similar color perception and translucency to those by conventional sintering.

• The Journal of Advanced Prosthodontics
• /
• v.5 no.4
• /
• pp.485-493
• /
• 2013

PURPOSE. To evaluate the effects of surface treatments on shear bond strength (SBS) between microwave and conventionally sintered zirconia core/veneers. MATERIALS AND METHODS. 96 disc shaped Noritake Alliance zirconia specimens were fabricated using YenaDent CAM unit and were divided in 2 groups with respect to microwave or conventional methods (n=48/group). Surface roughness (Ra) evaluation was made with a profilometer on randomly selected microwave (n=10) and conventionally sintered (n=10) cores. Specimens were then assessed into 4 subgroups according to surface treatments applied (n=12/group). Groups for microwave (M) and conventionally (C) sintered core specimens were as follows; $M_C$,$C_C$: untreated (control group), $M_1,C_1:Al_2O_3$ sandblasting, $M_2,C_2$:liner, $M_3,C_3:Al_2O_3$ sandblasting followed by liner. Veneer ceramic was fired on zirconia cores and specimens were thermocycled (6000 cycles between $5^{\circ}-55^{\circ}C$). All specimens were subjected to SBS test using a universal testing machine at 0.5 mm/min, failure were evaluated under an optical microscope. Data were statistically analyzed using Shapiro Wilk, Levene, Post-hoc Tukey HSD and Student's t tests, Two-Way-Variance- Analysis and One-Way-Variance-Analysis (${\alpha}$=.05). RESULTS. Conventionally sintered specimens ($1.06{\pm}0.32{\mu}m$) showed rougher surfaces compared to microwave sintered ones ($0.76{\pm}0.32{\mu}m$)(P=.046), however, no correlation was found between SBS and surface roughness (r=-0.109, P=.658). The statistical comparison of the shear bond strengths of $C_3$ and $C_1$ group (P=.015); $C_C$ and $M_C$ group (P=.004) and $C_3$ and $M_3$ group presented statistically higher (P=.005) values. While adhesive failure was not seen in any of the groups, cohesive and combined patterns were seen in all groups. CONCLUSION. Based on the results of this in-vitro study, $Al_2O_{3-}$ sandblasting followed by liner application on conventionally sintered zirconia cores may be preferred to enhance bond strength.

• Journal of the Korean Ceramic Society
• /
• v.29 no.4
• /
• pp.305-311
• /
• 1992

As compared with conventional sintering, rapid heating in microwave system could enhance sinterability and final properties of alumina with a very short sintering time. In this study microwave sintering was performed using zirconia brick as a reaction chamber which was positioned in a 2.45 GHz(700 W) multimode microwave cavity. Microwave-sintered alumina showed high density and smaller grain size than conventionally sintered alumina because the ratio of densification rate/grain growth rate was increased by rapid heating.

• Journal of the Korean Ceramic Society
• /
• v.35 no.11
• /
• pp.1197-1202
• /
• 1998

To check the possibility for microwave sintering of MLCC(multi layer ceramic capacitor) the tape cast-ed BaTiO3 thick films in zirconia insulation box were sintered by the domestic microwave oven. Microwave sintered samples had higher density lower porosity than coventionally sintered ones. but they didn't show Z5U electrical properties due to short sintering time about 15 minutes.

• Korean Journal of Materials Research
• /
• v.6 no.6
• /
• pp.576-584
• /
• 1996

The zirconia-alumina composite, a low loss material, was sucessfully sintered using a 2.45 GHz microwave radiation. The dense zirconia was used as a microware coupling aid. The effect of microwave power level on the heating rates of samples and the feasibility of microwave energy use in processign ceramec materials were obtained. It was also obtained how to accurately measure the temperature. According to the microwave heating theory, heating mechanisms were discussed.

• Journal of Dental Rehabilitation and Applied Science
• /
• v.25 no.2
• /
• pp.95-107
• /
• 2009

The purpose of this research was to examine the fitness of zirconia cores that were made by different sintering methods; generic electricity furnace and microwave furnace. Firstly, 12 cores for each group were made by using each different sintering process and attached them to a metal die with silicon. The internal and marginal gap of sintered zirconia was measured by using Skyscan 1076 micro-CT, then it was reorganized by CT-An software. To each samples, we extracted B-L image, M-D image of cutting side, and cross-sectional side of tooth long axis and calculated the mean value of marginal, axial, and occlusal gap each side. Results: 1. The mean marginal gap of sintered zirconia was $36.20{\mu}m$ for EVE, $47.67{\mu}m$ for LAV, $52.47{\mu}m$ for DEN, and $54.63{\mu}m$ for CER. 2. For the axial wall, the research showed the largest value of $63.49{\mu}m$ for EVE, but there were no statistical significance. 3. In related to the occlusal internal measurement, DEN showed the smallest value ($77.06{\mu}m$), EVE and CER showed significantly high value. From this study, it is suggested that CAD/CAM zirconia core which was made in the process of microwave sintering has clinically acceptable values in marginal and internal gap.

• The Journal of Advanced Prosthodontics
• /
• v.5 no.2
• /
• pp.161-166
• /
• 2013

PURPOSE. This study aimed to identify the effects of the sintering conditions of dental zirconia on the grain size and translucency. MATERIALS AND METHODS. Ten specimens of each of two commercial brands of zirconia (Lava and KaVo) were made and sintered under five different conditions. Microwave sintering (MS) and conventional sintering (CS) methods were used to fabricate zirconia specimens. The dwelling time was 20 minutes for MS and 20 minutes, 2, 10, and 40 hours for CS. The density and the grain size of the sintered zirconia blocks were measured. Total transmission measurements were taken using a spectrophotometer. Two-way analysis of variance model was used for the analysis and performed at a type-one error rate of 0.05. RESULTS. There was no significant difference in density between brands and sintering conditions. The mean grain size increased according to sintering conditions as follows: MS-20 min, CS-20 min, CS-2 hr, CS-10 hr, and CS-40 hr for both brands. The mean grain size ranged from 347-1,512 nm for Lava and 373-1,481 nm for KaVo. The mean light transmittance values of Lava and KaVo were 28.39-34.48% and 28.09-30.50%, respectively. CONCLUSION. Different sintering conditions resulted in differences in grain size and light transmittance. To obtain more translucent dental zirconia restorations, shorter sintering times should be considered.

• Journal of Electrochemical Science and Technology
• /
• v.13 no.3
• /
• pp.390-397
• /
• 2022

The use of microwaves as the energy source for synthesis and sintering of ceramics offers substantial advantages compared to conventional gas-fired and electric resistance furnaces. Benefits include much shorter processing times and reaching the sintering temperature more quickly, resulting in superior final product quality. Most oxide ceramics poorly interact with microwave irradiation at low temperatures; thus, a more complex setup including a susceptor is needed, which makes the whole process very complicated. This investigation pursued a new approach, which enabled us to use microwave irradiation directly in poorly coupled oxides. In many solid-state electrochemical devices, the support is either metal or can be reduced to metal. Metal powders in the support can act as an internal susceptor and heat the entire cell. Then sufficient interaction of microwave irradiation and ceramic material can occur as the sample temperature increases. This microwave heating and exothermic reaction of oxidation of the support can sinter the ceramic very efficiently without any external susceptor. In this study, yttria stabilized zirconia (YSZ) and a Ni-YSZ cermet support were used as an example. The cermet was used as the support, and a YSZ electrolyte was coated and sintered directly using microwave irradiation without the use of any susceptor. The results were compared to a similar cell prepared using a conventional electric furnace. The leakage test and full cell power measurement results revealed a fully leak-free electrolyte. Scanning electron microscopy and density measurements show that microwave sintered samples have lower open porosity in the electrode support than conventional heat treatment. This technique offers an efficient way to directly use microwave irradiation to sinter thin film ceramics without a susceptor.