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Sustained antibacterial effects of antibacterial agents against Streptococcus mutans applied on hydroxyapatite disc

Ju-Lee SON ; SSun IM ; Dong-Hyun GIM ; Seunghan OH ; Ji-Myung BAE

Korean Journal of Dental Materials.2020;47(4):245-252. doi:10.14815/kjdm.2020.47.4.245

This study aimed to evaluate the antibacterial activities sustainability of antibacterial agents mixed with experimental fluoride varnish on hydroxyapatite disc against Streptococcus mutans (S. mutans). On the hydroxyapatite disc with 4.8 mm of diameter, 5 μL of 1 mM antibacterial agents mixed with experimental fluoride varnish were applied. Positive control and vehicle control were 10 μg/mL ampicillin and dimethyl sulfoxide (DMSO) mixed with fluoride varnish, respectively. The discs were stored in distilled water in a 37℃ shaking water bath at 120 rpm for 30 minutes, 4 hours, 1 day, 5 days, 20 days, and 30 days. Antibacterial activities were evaluated with the inhibition zone by the agar diffusion test. The antibacterial activities of all antibacterial agents were sustained for 30 days. Among them, Bakuchiol, Bavachromene, and Bavachalcone showed higher antibacterial activities for up to 30 days. The antibacterial agents when mixed in the experimental fluoride varnish with increased and prolonged antibacterial activities can be applied to prevent dental caries effectively.

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Efficacy of the extract of Brachypodium sylvaticum as a preventive and an improving agent of periodontal disease

Seong-Hee MOON ; Ju-Lee SON ; Seong-Jin SHIN ; Seunghan OH ; Seong Hwan KIM ; Ji-Myung BAE

Korean Journal of Dental Materials.2020;47(4):235-244. doi:10.14815/kjdm.2020.47.4.235

We evaluated the antibacterial, anti-inflammatory, and inhibitory effect of osteoclast differentiation of Brachypodium sylvaticum (BS) to find out the possibility of preventing periodontal disease. The inhibition of Porphyromonas gingivalis (P. gingivalis) growth by BS and the sustainability of the antibacterial activity was assessed. The production of pro-inflammatory cytokines from lipopolysaccharide (LPS)-induced RAW 264.7 cells were measured using enzyme-linked immunosorbent assays (ELISA), and the production of nitric oxide (NO) and cell viability were measured. Osteoclast differentiation was evaluated by Tartrate-resistant acid phosphatase (TRAP) staining, and TRAP activity. BS showed significant antibacterial activity and sustainable antibacterial activity in P. gingivalis. We also found out that the BS significantly decreased secretion of pro-inflammatory cytokines [tumor necrosis factor (TNF-α) and interleukin-6 (IL-6)] and NO production without cytotoxicity. Furthermore, BS inhibited the differentiation of bone marrow macrophages (BMMs) obtained from mouse bone marrow cells into osteoclasts without cytotoxicity. Taken together, BS can be a promising candidate for a preventive and improving agent of periodontal disease having antibacterial, anti-inflammatory, and inhibitory effects of osteoclast differentiation.

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Effect of sintering condition and aging on hardness and optical properties of monolithic zirconia

Moon-Chun KONG ; Mi-Gyoung PARK

Korean Journal of Dental Materials.2020;47(4):221-234. doi:10.14815/kjdm.2020.47.4.221

The purpose of this study was to examine the effect of hardness and optical properties of dental zirconia in accordance to sintering condition and aging. 10.0 mm×10.0 mm×1.5 mm zirconia specimens were prepared using Luxen Enamel E2.According to aging, zirconia specimens were sintered under fifteen different conditions. Specimens were divided into six subgroup and sintered with various durations (4 h, 5 h, 6 h, 7 h, and 12 h) at the various maximum temperature (1,500℃, 1,530℃, and 1,560℃). The hardness was measured four times per specimen using a Micro Vickers hardness tester, CIE L * , a * , b * values of each specimen were measured using a spectrophotometer and the TP values were calculated for translucency comparison.In the specimen with aging, there was a difference in hardness according to the sintering temperature, but there was no difference in hardness according to the sintering time. In the specimen with aging, as sintering temperature increased, CIE L * , a * , b * values decreased, resulting in a decrease in brightness and tendency of green and blue trends. In the specimen with aging, there was no change in L * value with decreasing sintering time and as sintering time decreased, CIE a * , b * values decreased, resulting in tendency of green and blue. In the specimen with aging, even if the sintering time decreases from 12 hours to 5 hours, there was no reduce in TP values.

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Effect of investment materials on 3-point flexural strength of heat pressed zirconia core

Tae-Yeon KIM ; Seha KIM ; Jeong-Hui JI ; Byoung gu LIM ; Sung Geun OH ; Jaewoo SHIN ; Junghwan LEE ; Min-Ho LEE ; Tae-Sung BAE

Korean Journal of Dental Materials.2020;47(4):211-220. doi:10.14815/kjdm.2020.47.4.211

The purpose of this study was to evaluate the effect of the reaction between investment material and zirconia on the strength of zirconia in the application of heat-pressing method. Sixty specimens were cut (24 mm×4 mm×0.5 mm) into plates from Zirtooth ™ Multi O-9814 block (∅98×14T, HASS, Gangwondo, Korea) and sintered at 1450℃. Specimens were divided into 6 subgroups according to the depending on the investement material; (a) UN group (Control), (b) PH group (Prime vest HS), (c) CP group (Calibra-press), (d) BV group (BC-Vest), (e) MH group (Microstar-HS), (f) F1 group (Formula 1). Five investment materials were buried according to the procedure recommended by the manufacturer and left at room temperature for 30 minutes. The investment mold was dried and maintained at an elevated temperature of 850℃ for 50 minutes. Then, Amber Lisi-POZ LT (HASS) was placed in a thermoformed electric furnace (Programat EP3000/G2, Ivoclar Vivadent, Schaan, Liechtenstein) together with the mold, heated to 915℃ at an elevation temperature of 45℃/min, and moored for 15 minutes. The specimens were loaded to fracture in a universal testing machine and the fracture surface was examined by a field-emission scanning electron microscopy (FE-SEM). The surface of the zirconia specimen with the investment material was analyzed by energy dispersive X-ray spectroscopy (EDS). The 3-point flexural strength test showed the highest value (1265.5 MPa) in the UN group and the lowest value (756.1 MPa) in the F1 group. As a result of EDS analysis, the largest amount of Si was detected in the F1 group, and the most interfacial changes occurred as a result of FE-SEM analysis. It was concluded that when the zirconia is buried with the investment material and the heat press molding is performed, the state of the interface is changed due to the investment material at the bonding interface while the strength is lowered.

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Antibacterial sustainability of experimental fluoride varnish added with adhesive components

Seong-Jin SHIN ; Ju-Lee SON ; Seunghan OH ; Ji-Myung BAE

Korean Journal of Dental Materials.2020;47(4):203-210. doi:10.14815/kjdm.2020.47.4.203

The purpose of this study was to evaluate the sustainability of antibacterial effect against Streptococcus mutans of experimental fluoride varnish mixed with 2-hydroxyethyl methacrylate (HEMA) and/or glutaraldehyde. Experimental fluoride varnish (EX1) was fabricated. To make fluoride varnish with adhesive materials, EX1 was mixed with 5 wt% of glutaraldehyde (EX2), 35 wt% of HEMA (EX3) or both 5 wt% of glutaraldehyde and 35 wt% of HEMA (EX4). 5 μL of each experimental group was applied to 6 mm diameter polyethylene terephthalate film discs. Disks were stored in distilled water in a shaking incubator at 37℃ for 1 hour, 3 hours, 8 hours, 12 hours, 24 hours, 5 days and 10 days. The antibacterial activities against S. mutans were evaluated by agar diffusion test with the discs at each time. The antibacterial activities were sustained up to 10 days in all groups. The antibacterial activities of EX3 and EX4 were significantly higher than other groups from 8 hours to 10 days and there were no significant differences from EX2 at 10 days. HEMA with and without glutaraldehyde can be applied to fluoride varnish to increase the sustainability of antibacterial activities.

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Temperature changes and compressive properties of bulk-fill composites by light curing

Dong-ho YI ; Hyo-Joung SEOL ; Yong Hoon KWON

Korean Journal of Dental Materials.2020;47(4):193-202. doi:10.14815/kjdm.2020.47.4.193

The purpose of the present study was to assess the temperature change and compressive property of bulk-fill composites (BFCs) by the light curing. Seven resin-based composites (RBCs), including five BFCs, were chosen to evaluate their maximum temperature rise and exothermic heat during and after light curing and compressive strength (CS) and modulus (CM) for 4-mm thick state. Light attenuation coefficients (ACs) showed reasonably high correlation with filler content (vol% and wt%).Except one resin product, AC values of BFCs were lower than those of RBCs tested. All the tested specimens showed temperature rise (9.8-23.6℃) and exothermic heat (4.2-18.3℃) for 4-mm thick case. CS and CM values of the tested specimens ranged approximately 69 to 116 MPa and 1.3 to 2.8 GPa, respectively. The difference of temperature changes and compressive properties (CS and CM) between BFCs and RBCs was not consistent and had no statistically consistent significance.

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The effect of cooling rate on hardness and microstructure of a metal-ceramic Au-Pt-Pd alloy during simulated firing

Ji-In JEONG ; Hye-Jeong SHIN ; Yong-Hoon KWON ; Hyo-Joung SEOL

Korean Journal of Dental Materials.2020;47(4):181-192. doi:10.14815/kjdm.2020.47.4.181

In this study, Au-Pt-Pd metal-ceramic alloy was examined by varying cooling rate during simulated porcelain firing cycles to investigate the effect of cooling rate on hardness and related microstructure during simulated firing. The final hardness was different according to the cooling rate after the simulated porcelain firing cycles. The reduction in hardness value was smaller after cooling at the faster cooling rate (Stage 0) than the value after slower rate (Stage 3). In the ice-quenched specimens after oxidation treatment (OXI-IQ), homogenization was slightly occurred, and the hardness decreased apparently compared to that of the as-cast specimens (AS-CAST). In the specimens cooled at Stage 0 and Stage 3 after oxidation, the hardness increased apparently compared to the ice-quenched specimens, even though the hardness decreased later by further firing simulation.The final hardness was lower in the specimen cooled at the slower rate (Stage 3) than the faster rate (Stage 0), and it seems to be due to the coarsening of the microstructure. The matrix and precipitates were consisted of FCC (face-centered-cubic) structure rich in Au. The Au content was higher in the matrix and the Pt content was higher in the precipitates, which corresponded to the Au-Pt binary phase diagram.

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Research and development of dental assistant robot

In-gyu BAEK ; Jin-soo AHN

Korean Journal of Dental Materials.2020;47(4):169-180. doi:10.14815/kjdm.2020.47.4.169

COVID-19 situation has raised the risk of air-borne diseases in dental offices, while dental clinic and hospitals are facing difficulties hiring dental assistants for many reasons. To solve this problem, a prototype of dental assistant robot that can effectively block aerosols from the patient’s mouth and replace simple tasks of the dental assistants was researched and developed. The ultimate specific goal of the function intended to be implemented was “to enable preparations of lower molar teeth by dentist alone.” Although it was possible to achieve the goal with the first prototype, improvements are needed to improve efficiency and stability. Through continuous improvement and development, dental assistant robots are expected to be of great help to patients, medical assistants, and dentists.

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Effect of fabrication method of lithium disilicate crown on fitness

Su-Yeon CHOI ; Seha KIM ; Jeong-Hui JI ; Min-Ho LEE ; Tae-Sung BAE

Korean Journal of Dental Materials.2020;47(3):157-168. doi:10.14815/kjdm.2020.47.3.157

The purpose of this study was to evaluate the influence of fabrication methods of lithium disilicate reinforced glass-ceramic crown on marginal and internal fit. Lithium disilicate reinforced glass-ceramic crowns were fabricated using ingots for heat press forming and blocks for CAD/CAM milling manufactured by Hass and Ivoclar/Vivadent. Dentiform of maxillary central incisor was prepared with a 6°taper and 1 mm deep chamfer margin and duplicated with silicone. Then the polyurethane resin was poured at silicone mold to produce working model. Marginal and internal fit were measured by the silicone replica technique. Each silicon replica was cut into labio-lingual and mesio-distal sections and the thickness of the light body silicon was measured. Fourteen reference points were determined and measured using a microscope. As a result of calculating and comparing the average value of 14 points in all groups, the measured value was within 120 µm, the clinically acceptable range suggested by previous literatures. In all groups, the marginal fit was smaller than the internal fit. At the margin area, significant differences were identified only between the ECM group and the EPM group, and there was no statistically significant difference between the remaining groups. At the deep chamfer area, the ECM and ABM group produced by the CAD system had excellent compatibility. In the axial wall and incisal area, ECM was superior to both EPC and EPM. Also, both ABM and APC groups were statistically significantly superior than APM.

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Research on zirconium alloys with low elastic modulus and low magnetic susceptibility for improving bone resorption and susceptibility artifacts

Chang-Yong LEE ; Chung-Seok KIM ; Yeong-Mu KO

Korean Journal of Dental Materials.2020;47(3):143-156. doi:10.14815/kjdm.2020.47.3.143

The objective of this study was to fabricate Zr-Cu alloys with low elastic modulus and low magnetic susceptibility for the use as the dental biomaterials. Metallic implants, such as stainless steel, Co-Cr alloys, and Ti alloys, could be magnetized in the strong magnetic field of the MRI instrument and produce artifacts (magnetic susceptibility artifacts) on the image. The areas that cause the artifacts on images are closely related to the magnetic susceptibility. This susceptibility artifact is caused by metals, such as Ti, Co, and stainless steels, inside the body. Therefore, metallic implants with a low magnetic susceptibility are preferable for surgery performed with the assistance of an MRI. Recently, Zr-based alloys have been attracting interests as biomaterials due to their excellent mechanical properties and low magnetic susceptibility. The magnetic susceptibility of Zr-Nb was half that of Ti-6Al-4V. In addition, the magnetic susceptibility of Zr-Mo was reported almost one-third that of commercially pure Ti and Ti-6Al-4V alloy.However, there are limited reports concerning metallic biomaterials with low magnetic susceptibility for dental applications. The magnetic susceptibility of the Zr-Cu binary alloys was extremely low, approximately 10-7 ; this level is approximately one order less than that of pure Zr and other commercialized Ti-based metallic biomaterials. The Zr-Cu binary alloy exhibited moderate compressive strength (1261~1565 MPa), yield stress (432~595 MPa), favorable elongation (14~34%), high elastic energy (7.2~19.3 MJ/㎥ ) and low elastic modulus (20~28 GPa). Consequently, Zr-Cu binary alloys have the potential to be used as biomaterials with nullifying magnetic properties for magnetic resonance imaging diagnosis and a good combination of mechanical properties indicates them potential biomaterials for biological hard tissue materials

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