• Journal of the Korean Ceramic Society
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• v.18 no.3
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• pp.163-170
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• 1981

The crystallization of $Li_2O-SiO_2$ system glasses and the effect of phase separtion to crystal nucleation were studied. The crystallization temperatures of various glasses were determined by DTA and glasses were nucleation heat treated at the temperatures ranging from 45$0^{\circ}C$ to 5$25^{\circ}C$. These glasses were thengown at $700^{\circ}C$ to observable size in the optical microscope. Crystal nucleation rates of various glasses were obtained by estimating the number of crystals per unit volume. The main crystal phase of these glasses identified by X-ray diffraction was lithium disilicate ($Li_2O$.$2SiO_2$). It was found that the crystal nucleation rate of glass (19.5% $Li_2P$-80.5% $SiO_2$), the nearest composition to lithium disilicate, was higher than other glasses. The opalescence caused by phase separation was observed in the nucleation heat treated glass (16.3% $Li_2O$-83.7% $SiO_2$). The result from nucleation density measurement of this glass indicated that the nucleation was enhanced during early stage of phase separation. The molphologies of crystals in glasses and crystal growth rate at $600^{\circ}C$ were also discussed.

• The Journal of Korean Academy of Prosthodontics
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• v.62 no.1
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• pp.20-27
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• 2024

As a high-performance polymer, Polyetherketoneketone (PEKK) has good biocompatibility and excellent physical properties and is used in several areas, including dentistry. Many successful cases of implant-supported fixed prostheses with a PEKK framework have been reported; however, a long-term observation of the reported cases and discussion of complications are not available. In this case report, we present three cases of implant-supported fixed prostheses with a PEKK framework veneered with composite resin, lithium disilicate crown, and high-impact polymethyl methacrylate (PMMA), and discuss their 6-year follow-up results.

• Journal of the Korean Ceramic Society
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• v.25 no.5
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• pp.431-436
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• 1988

The properties of scid-resistance to boiling HCl, thermal expansion coefficient and softening temperature of mother glass and glass-ceramic of LAS systems were investigated at the contents of SiO2 varing from 57 to 67wt%. The nucleation and growth of crystalline phase of LAS compositions were carried out at 50$0^{\circ}C$ and $700^{\circ}C$. The crystalline phase jconsists of lithium alumino silicate, lithum meta silicate, lithium disilicate, $\alpha$-crystobalite and $\alpha$-quartz. Lithium alumino silicate(virgilite) is the major crystalline phase in the glass ceramics. The degree of acid resistant property was increased in proportion with the silica content for both glass and ceramics. Glass-ceramic gives lower acid-resistance and thermal expansion coefficient while softening temperature shows higher for glass-ceramic than for mother glass.

• Korean Journal of Materials Research
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• v.26 no.1
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• pp.54-60
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• 2016

We have investigated the crystallization mechanism of the lithium disilicate ($Li_2O-2SiO_2$, LSO) glass particles with different sizes by isothermal and non-isothermal processes. The LSO glass was fabricated by rapid quenching of melt. X-ray diffraction and differential scanning calorimetry measurements were performed. Different crystallization models of Johnson-Mehl-Avrami, modified Ozawa and Arrhenius were adopted to analyze the thermal measurements. The activation energy E and the Avrami exponent n, which describe a crystallization mechanism, were obtained for three different glass particle sizes. Values of E and n for the glass particle with size under $45{\mu}m$, $75{\sim}106{\mu}m$, and $125{\sim}150{\mu}m$, were 2.28 eV, 2.21 eV, 2.19 eV, and ~1.5 for the isothermal process, respectively. Those values for the non-isothermal process were 2.4 eV, 2.3 eV, 2.2 eV, and ~1.3, for the isothermal process, respectively. The obtained values of the crystallization parameters indicate that the crystallization occurs through the decreasing nucleation rate with a diffusion controlled growth, irrespective to the particle sizes. It is also concluded that the smaller glass particles require the higher heat absorption to be crystallized.

• The Journal of Advanced Prosthodontics
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• v.15 no.5
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• pp.238-247
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• 2023

PURPOSE. The purpose of this study was to assess the effect of resin cement shade on the color of different novel ultratranslucent monolithic zirconia and lithium disilicate veneer materials. MATERIALS AND METHODS. For a total of 40 specimens, flat cylindrical discs with a 9-mm diameter and 0.5-mm thickness were created using CAD/CAM technology. The specimens were divided into five groups according to their material (n = 8) (e.max, Prettau, Aidite, Shofu and Dima) using A1 shade. Resin discs with the same diameter and shade as the specimens served as tooth-colored substructures. Three shades (neutral, light and warm) of resin cement try-in pastes (Variolink Esthetic LC) were used as the luting cement material. The color of each material group was measured before and after cementation using the three cement shades, and the CIE L^*a^*b^* coordinates were obtained with a spectrophotometer. Values for the translucency parameter (TP) and color change delta E (E) before (baseline) and after cementation of each specimen were determined. To compare differences among the material groups within each shade of cement and among various shades of cement within each material, the data were analyzed using one-way ANOVA and post hoc testing. RESULTS. Color coordinates L^*, a^* and b^* significantly changed after the application of try-in pastes relative to baseline values, with a noticeable decrease in lightness (L^*) (P < .05). A significant color change (ΔE) was observed in all tested materials after cementation, with ΔE values exceeding 3.3 (P < .05). Although TP changed after cementation for most materials tested, these changes were not statistically significant (P > .05). Shofu and Dima ceramics showed the lowest TP values, while Aidite and Prettau showed the highest TP values. For e.max, translucency decreased after cementation with neutral and warm shades, and it significantly increased after cementation with a light shade. CONCLUSION. The shade of cement significantly altered the final color of the ceramic veneer material to a level above the threshold at which the clinical perception of color change occurred (> 3.3). The TP was not influenced by the cement shade. The translucency levels of the novel ultratranslucent multilayer monolithic zirconia ceramics Aidite and Prettau were higher than that of the lithium disilicate e.max material.

• The Korean Journal of Ceramics
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• v.5 no.4
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• pp.363-367
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• 1999

New glass ceramics were investigated for the application as substrates to be used in hard disk devices. The glass system to precipitate lithium di-silicate was studied so as to optimize the composition to realize very high surface flatness. The addition of small amount of several metal oxides with high valences had very drastic effects on the microstructure, because they played a role of crystallization agents, and consequently it determined surface flatness even after the polishing process. The possible mechanism changes of crystal growth due to the addition of metal oxides were discussed in relation to the final micro-texture development. The glass ceramics with very high surface flatness(Ra=7.1 $\AA$) was obtained by the addition of the mixture of $P-2O_5 \;and \;MoO_3$ as crystallization agents.

• The Journal of Advanced Prosthodontics
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• v.8 no.2
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• pp.75-84
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• 2016

PURPOSE. To evaluate the effect of various surface treatments on the surface structure and shear bond strength (SBS) of different ceramics. MATERIALS AND METHODS. 288 specimens (lithium-disilicate, leucite-reinforced, and glass infiltrated zirconia) were first divided into two groups according to the resin cement used, and were later divided into four groups according to the given surface treatments: G1 (hydrofluoric acid (HF)+silane), G2 (silane alone-no heat-treatment), G3 (silane alone-then dried with $60^{\circ}C$ heat-treatment), and G4 (silane alonethen dried with $100^{\circ}C$ heat-treatment). Two different adhesive luting systems were applied onto the ceramic discs in all groups. SBS (in MPa) was calculated from the failure load per bonded area (in $N/mm^2$). Subsequently, one specimen from each group was prepared for SEM evaluation of the separated-resin-ceramic interface. RESULTS. SBS values of G1 were significantly higher than those of the other groups in the lithium disilicate ceramic and leucite reinforced ceramic, and the SBS values of G4 and G1 were significantly higher than those of G2 and G3 in glass infiltrated zirconia. The three-way ANOVA revealed that the SBS values were significantly affected by the type of resin cement (P<.001). FIN ceramics had the highest rate of cohesive failure on the ceramic surfaces than other ceramic groups. AFM images showed that the surface treatment groups exhibited similar topographies, except the group treated with HF. CONCLUSION. The heat treatment was not sufficient to achieve high SBS values as compared with HF acid etching. The surface topography of ceramics was affected by surface treatments.

• Journal of the Korean Academy of Esthetic Dentistry
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• v.25 no.2
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• pp.79-87
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• 2016

Single visit monolithic restoration can be proceed with digital workflow which consist of intraoral scanning, dental CAD(computer aided design) and restoration milling with CAM(Computer aided manufacturing). While zirconia has more than 900MPa of flexural strength compared with 400MPa for lithium disilicate, shortened fabricating time of lithium disilicate is considered to be a better choice for fabricating single visit full contour monolithic restoration. However, new zirconia materials which are TZI C(Dentsply Sirona) and LUXEN Enamel(Dental Max), new induction heating method of sintering furnace, and new sintering protocols for MoSi2 heating elements sintering furnace offer significantly reduction of full contour monolithic zirconia restoration fabrication time with greater translucency. These new developments lead single visit zirconia restoration in reality.

• The Journal of Advanced Prosthodontics
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• v.6 no.3
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• pp.151-156
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• 2014

PURPOSE. To investigate the microtensile bond strength between two all-ceramic systems; lithium disilicate glass ceramic and zirconia core ceramics bonded with their corresponding glass veneers. MATERIALS AND METHODS. Blocks of core ceramics (IPS e.max$^{(R)}$ Press and Lava$^{TM}$ Frame) were fabricated and veneered with their corresponding glass veneers. The bilayered blocks were cut into microbars; 8 mm in length and $1mm^2$ in cross-sectional area (n = 30/group). Additionally, monolithic microbars of these two veneers (IPS e.max$^{(R)}$ Ceram and LavaTM Ceram; n = 30/group) were also prepared. The obtained microbars were tested in tension until fracture, and the fracture surfaces of the microbars were examined with fluorescent black light and scanning electron microscope (SEM) to identify the mode of failure. One-way ANOVA and the Dunnett's T3 test were performed to determine significant differences of the mean microtensile bond strength at a significance level of 0.05. RESULTS. The mean microtensile bond strength of IPS e.max$^{(R)}$ Press/IPS e.max$^{(R)}$ Ceram ($43.40{\pm}5.51$ MPa) was significantly greater than that of Lava$^{TM}$ Frame/Lava$^{TM}$ Ceram ($31.71{\pm}7.03$ MPa)(P<.001). Fluorescent black light and SEM analysis showed that most of the tested microbars failed cohesively in the veneer layer. Furthermore, the bond strength of Lava$^{TM}$ Frame/Lava$^{TM}$ Ceram was comparable to the tensile strength of monolithic glass veneer of Lava$^{TM}$ Ceram, while the bond strength of bilayered IPS e.max$^{(R)}$ Press/IPS e.max$^{(R)}$ Ceram was significantly greater than tensile strength of monolithic IPS e.max$^{(R)}$ Ceram. CONCLUSION. Because fracture site occurred mostly in the glass veneer and most failures were away from the interfacial zone, microtensile bond test may not be a suitable test for bonding integrity. Fracture mechanics approach such as fracture toughness of the interface may be more appropriate to represent the bonding quality between two materials.

• The Journal of Advanced Prosthodontics
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• v.11 no.1
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• pp.23-31
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• 2019

PURPOSE. To investigate and compare the surface roughness (SR), weight and height of monolithic zirconia (MZ), ceramometal (CM), lithium disilicate glass ceramic (LD), composite resin (CR), and their antagonistic human teeth enamel. MATERIALS AND METHODS. 32 disc shaped specimens for the four test materials (n=8) and 32 premolars were prepared and randomly divided. SR, weight and height of the materials and the antagonist enamel were recorded before and after subjecting the specimens to 240,000 wear-cycles ($49N/0.8Hz/5^{\circ}C/50^{\circ}C$). SR, height, weight, and digital microscopic qualitative evaluation were measured. RESULTS. CM ($0.23+0.08{\mu}m$) and LD ($0.68+0.16{\mu}m$) exhibited the least and highest mean difference in the SR, respectively. ANOVA revealed significance (P=.001) between the materials for the SR. Paired T-Test showed significance (P<.05) for the pre- and post- SR for all the materials. For the antagonistic enamel, no significance (P=.987) was found between the groups. However, the pre- and post- SR values of all the enamel groups were significant (P<.05). Wear cycles had significant effect on enamel weight loss against all the materials (P<.05). CR and MZ showed the lowest and highest height loss of 0.14 mm and 0.46 mm, respectively. CONCLUSION. MZ and CM are more resistant to SR against the enamel than LD and CR. Enamel worn against test materials showed similar SR. Significant variations in SR values for the tested materials (MZ, LD, CM, and CR) against the enamel were found. Wear simulation significantly affected the enamel weight loss against all the materials, and enamel antagonist against MZ and CM showed more height loss.