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Mechanical properties and biocompatibility of experimental 3D printing denture base resin

Korean Journal of Dental Materials.2019;46(4):253-262. doi:10.14815/kjdm.2019.46.4.253

This study was conducted to compare the flexural properties and biocompatibility of experimental 3D printing resins with commercial 3D-printing resins and conventional denture base resin. Auto polymerized pour-type denture base resin (RESS LT; Retec, Germany) was used as a control group. A commercial 3D printing denture base resin, NextDent (Base, Vertex Dental, Soesterberg, Netherlands) and two 3D printing resins, White prototyping resin (PR57-W, Autodesk, USA) and Clear prototyping resin (PR48, Autodes, usa) were compared. Experimental 3D printing resins (E1, E2, E3) were made with different ratios of dimethacrylates. DLP 3D printer (VIDA, Envisiontec) was used for 3D printing. The specimens (64Ã—10Ã—3.3 mm) were made based on the protocol of ISO 20795-1. The flexural strength and flexural modulus were measured by a universal testing machine (Z020, Zwick, Germany) at a crosshead speed of 5 mm/min. MTT test was performed to evaluate the cell viability. The flexural strength and flexural modulus of E2 were significantly higher than those of other groups (p<0.05). Biocompatibility of all experimental 3D printing resins were not significantly different from negative group (p>0.05). E2 is considered to be a promising material as a denture base resin for 3D printing.

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Effect of silane and alkali treatment on the shear bond strength between two Ni-Cr alloys and acrylic resin

Kwang Sig PARK1 ; Tae Yub KWON

Korean Journal of Dental Materials.2019;46(4):243-252. doi:10.14815/kjdm.2019.46.4.243

Sufficient bonding between the framework of the cast alloy and the denture base resin is essential for the clinical success of removable partial dentures. In this study, we investigated whether the silane and alkali treatments improve the chemical bonding between two nickel-chromium alloys and acrylic resin and thus the shear bond strength. A silane solution was prepared using 3-methacryloxypropyltrimethoxysilane. The alloy specimens were treated with silane and alkali, preparing four experimental groups: untreated (UT), silane treated (ST), alkali treated (AT), and alkali/silane treated (AST) groups. In addition, the contact angles and surface roughness of the alloy surfaces of the four groups were measured. The acrylic resin was bonded to the alloy specimens, and then the resin was polymerized to form a bonded specimen. After measuring the shear bond strength, the failure modes were examined using scanning electron microscopy. Results for all groups were analyzed using two-way ANOVA followed by Tukey's multiple comparison test at a significance level of 0.05. The statistical analysis showed no significant differences in Ra value for all groups (p>.05). In the two alloys, the contact angle of the AT group was significantly lower than that of the other groups (p<.05), and that of the AST group was significantly higher than that of the ST group (p<.05). In both alloys, the ST and AST groups showed the higher shear bond strengths (p<.05), while the UT and AT groups showed the lower values. The UT and AT groups showed complete adhesive failure at the fractured surfaces. In this study, the silane treatment was effective to improve the shear bond strength, but the alkali treatment did not show any significant effect.

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Changes in hardness and microstructure of a Pd-Ag-In-Ga-based metal-ceramic alloy during porcelain firing simulation and subsequent cooling

Hye Jeong SHIN ; Yong Hoon KWON ; Hyo Joung SEOL

Korean Journal of Dental Materials.2019;46(4):229-242. doi:10.14815/kjdm.2019.46.4.229

In this experiment, the alloy having the composition of 49.5Pd-40Ag-9In-1Ga (wt.%) was used to find the most effective cooling rate for the hardening of alloy during porcelain firing simulation. In each stage of firing simulation, ice-quenching or cooling at the most effective cooling rate for hardening of the alloy was done after firing to observe changes in the hardness and associated microstructures during the firing and subsequent cooling. For this purpose, the firing simulated alloy was characterized by analyzing the changes in hardness, microstructure, crystal structure and the elemental distribution. The hardness of alloy decreased by cooling after oxidation treatment, which was induced by the homogenization of the specimen. In this alloy, the most effective cooling rate for alloy hardening after oxidation treatment was Stage 0. During the porcelain firing simulation until the final firing stage, the cooling rate was set to Stage 0, and the complete firing simulation was performed until the final firing stage, Glaze. As a result, the final hardness of the metal substructure obtained after complete firing simulation was lower than that of the as-cast specimen. The decrease in hardness caused by the porcelain firing simulation results from a reduction in the interface between the precipitates of face-centered tetragonal structures and the matrix of face-centered cubic structures as the precipitates coarsen.

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3D architecture developments for spatial controls of periodontal ligament regeneration with angular orientations

Chan Ho PARK

Korean Journal of Dental Materials.2019;46(4):215-228. doi:10.14815/kjdm.2019.46.4.215

Various biomaterial-based, 3D architectures with micron-scaled geometries have been investigated for periodontal tissue neogenesis, and appropriate fabrication techniques for the scaffold manufacturing have been developed for pre-clinical or clinical situations. Periodontal tissues, the periodontal ligaments (PDLs), which are fibrous connective tissues between alveolar bone and cementum has been known as the major component that would generate biomechanical responses against mastication and occlusion. In particular, the angulations or orientations of PDL are critically important to transmit external stimuli and provide biomechanical adaptations for tooth-supporting functions. However, many studies still have demonstrated that optimal-biomechanical stimulations could re-make the configurations and orientations of PDL bundles with the low predictability in pre-clinical and clinical models. Here, we discussed the advanced technologies and geometric specifications for engineered PDL-guiding approaches spatiotemporally as 3D platforms.

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Mechanical properties and antibacterial effects of glass ionomer cement containing gallium phosphate glass (GPG)

Dong Ae KIM ; Gyu Ri KIM ; Jung Hwan LEE ; Hae Hyoung LEE

Korean Journal of Dental Materials.2019;46(4):205-214. doi:10.14815/kjdm.2019.46.4.205

This study investigated the mechanical properties and antibacterial activity of glass ionomer cement (GIC) containing 1 mol% or 5 mol% gallium phosphate glass (GPG) powder. GPG were added to conventional GIC powder in a range of 0~20 wt%. The specimens for compressive strength (4 mmÃ˜Ã—6 mm) and diametral tensile strength (6 mmÃ˜Ã—4 mm) were prepared by mixing with the cement liquid and kept in an water of 37Â±1â„ƒ. Mechanical properties were evaluated at an interval of 1 h, 24 h, and 7 days. Antibacterial activity of specimens against to S. mutans and S. sobrinus was evaluated using agar diffusion methods. Data were statistically analyzed by one-way ANOVA and Tukey HSD post-hoc test (p<0.05). Diametral tensile strength of GIC containing GPG were significantly higher than control GIC while compressive strength showed no statistical difference. There was an increasing tendency of antibacterial activity for GPG-GICs. Results indicated that GPG can be considered as potential reinforcing agent for increasing antibacterial and mechanical properties for conventional GIC.

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Effect of dentin surface treatment and exclusive primer on bond strength of a self-adhesive resin cement

Go Eun LIM ; Sung Ae SON ; Jeong Kil PARK

Korean Journal of Dental Materials.2019;46(4):195-204. doi:10.14815/kjdm.2019.46.4.195

The purpose of this study was to evaluate the effect of different dentin surface treatments on the bond strength of self-adhesive resin cement (G-CEM one). Human permanent molars were sectioned horizontally and standard smear layer was created. Teeth were divided into 4 groups according to the treatment methods: 1) no treatment, 2) 10% polyacrylic acid treatment, 3) exclusive primer (G-CEM one primer) treatment, 4) polyacrylic acid + exclusive primer treatment. After surface treatment, composite resin blocks were cemented with G-CEM one. After storage, specimens were cut into bars to measure the microtensile bond strength. Measured data were statistically analyzed. Confocal laser scanning microscopy was used to observe the bonding interface of cemented surface. Polyacrylic acid surface treatment group showed significantly lower ÂµTBS than other groups (p<0.05). ÂµTBS of exclusive primer treated groups was significantly higher than the control group (p<0.05). As a result, the exclusive primer improved dentin-cement bond strength. Polyacrylic acid treatment alone had negative effect on ÂµTBS of G-CEM one and dentin.

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Effect of glazing on the flexural strength of lithium disilicate glass ceramics

Jae Hoon SIM ; Joong Bae LEE ; Seong Sik HWANG

Korean Journal of Dental Materials.2019;46(4):185-194. doi:10.14815/kjdm.2019.46.4.185

The purpose of this study was to investigate the relationship between glazing treatment and flexural strength of dental lithium disilicate glass ceramics. Three commercial lithium disilicate glass ceramic blocks were cut to size and polished with abrasive papers and diamond pastes. The specimens were prepared in accordance to the manufacturer's instruction for the crystallization process and divided into three groups. The first group was over-glazed with glazing paste and liquid. The second group was self-glazed at a normal over-glazing temperature without glazing paste and liquid. The third group was an untreated control group. The three-point flexural test was carried out using the universal testing machine. The broken specimens were examined by SEM/EDS. The over-glazed group showed lowest flexural strength. There was no statistically significant difference between self-glazed group and untreated group with respect to flexural strength. The bubbles and cracks were found in the glaze layer of over-glazed group. As the tensile stress was concentrated at the bottom of glaze layer during the flexural test, it was evident that the bubbles played a role in initiation and propagation of cracks. A mixed layer formed between glaze layer and glass ceramic during the over-glazing process could have negative effects on the flexural strength of entire specimen.

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A study on the elution of residual monomers in three different denture base resins

Jong-Won KIM ; Sang-Hoon KIM ; Seung-Woo JEONG ; Hee-Jung KIM

Korean Journal of Dental Materials.2021;48(4):293-304. doi:10.14815/kjdm.2021.48.4.293

This study evaluated release of the residual monomer and cytotoxicity after polymerization of three denture base resins (heat curing resin, self-curing resin, light curing resin by 3D printer). Three types of resin specimen according to the manufacturer’s guideline were fabricated: heat curing resin (Group H), self-curing resin (Group S), 3D Printed resin (Group L). Each group of specimen were stored in distilled water at 37 ℃ for 1 day, 1 week, 2 weeks, 3 weeks, 4 weeks, 6 weeks, and 8 weeks in order to measure the release of the residual monomer. Absorbance was measured at each storage time in the three groups. Cytotoxicity is measured by MTT test at each storage time in the three groups. For statistical analysis, one-way ANOVA with post-hoc tests of Dunnett T3 test and Scheffe test were carried out, where p values of less than 0.05 were considered as significant. Group H showed the lower absorbance than Group S and Group L. There was no statistically significant difference in the absorbance of Group S and Group L for 8 weeks, except for the one day. Group H and Group S showed no cytotoxicity, but Group L resulted in cytotoxicity. To conclude, light curing resin used in 3D printer revealed high cytotoxicity in this study. In order to apply the 3D printed denture base resin to clinical situation, it is necessary to develop a method to reduce the release of residual monomers.

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Mechanical and physico-chemical properties of premixed-MTA in contact with three different types of solutions

Tae-Yun KANG ; Ji-Won CHOI ; Kwang-Mahn KIM ; Jae-Sung KWON

Korean Journal of Dental Materials.2021;48(4):281-292. doi:10.14815/kjdm.2021.48.4.281

The study aims to analyze the compressive strength, pH, and surface properties of mineral trioxide aggregates (MTA), which can be used as a pulp capping and root canal filling material. The tests were performed after immersing premixed types of MTA for seven days into three different solutions: simulated body fluid (SBF), saline, and distilled water (DW). A universal testing machine was used to measure the compressive strength after one and seven days of immersion. The un-immersed MTA was used as the control. To investigate the pH variation, MTA specimens were immersed in each solution and the pH was measured using a pH meter after 3, 6, 12, 24, 72, and 168 h. Changes on the MTA surface were also observed by SEM-EDS after seven days of immersion. Moreover, statistical analysis was performed by one-way ANOVA, Tukey's post-hoc test, and independent sample t-test. All experimental groups showed significantly higher compressive strengths compared to the control group (p<0.05). In addition, as the immersion time increased, the compressive strength gradually and significantly increased among all the groups. On the other hand, the difference was insignificant among solutions with the same immersion time (p>0.05). As the immersion time increased, the pH increased among all the groups, and the pH of samples immersed in saline and DW was significantly higher than that in SBF. The MTA surface immersed in each solution for seven days showed precipitates which mainly composed of Ca and Zr ions. Therefore, the type of contact solution does not significantly affect the compressive strength of MTA, but it significantly influences both the pH and surface condition

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Effect of cooling rate during porcelain firing on the optical properties of 3 mol% yttria-stabilized zirconia

Hye-Jeong SHIN ; Yong-Hoon KWON ; Hyo-Joung SEOL

Korean Journal of Dental Materials.2021;48(4):269-280. doi:10.14815/kjdm.2021.48.4.269

This study investigated the effect of the difference in the cooling rates on the optical properties of zirconia during the simulated firing of porcelain, without a porcelain layer on a zirconia core ceramic. No difference was observed in the average transmittance of zirconia with the cooling rate during simulated firing (p>0.05). In all groups, the average transmittance decreased from approximately 44% to approximately 28% (p<0.001) as the thickness increased from 0.51 mm to 2.0 mm. No difference was observed in the translucency and opalescence parameters of zirconia with the cooling rate during the simulated firing of porcelain (p>0.05). In all groups, the translucency decreased from approximately 16 to approximately 5 (p<0.001), while the opalescence increased from approximately 6 to approximately 11 (p<0.001) as the thickness increased from 0.51 mm to 2.00 mm. Thus, the average transmittance and translucency parameter decreased exponentially as the thickness increased in all groups regardless of the cooling rate during simulated porcelain firing, while the opalescence parameter increased in a parabolic manner. Therefore, in this study, even if porcelain is fired at a cooling rate higher or lower than the typical cooling rate when manufacturing a prosthesis with a zirconia core, the optical properties of zirconia are not expected to be significantly affected.

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