• Journal of the korean academy of Pediatric Dentistry
• /
• v.40 no.3
• /
• pp.177-184
• /
• 2013

Calcium hydroxide mixture medicaments can nearly be considered to be the ideal primary tooth filling material. However, long-term application of calcium hydroxide combinations as an intra canal medicament softens dentin. The aim of this study was to evaluate the effect of calcium hydroxide on the microhardness of root dentin of primary tooth. For the study, 60 extractedprimary incisors were divided into 3 groups (no medicament, calcium hydroxide/iodorform mixture, and calcium hydroxide/distilled water mixture). After the cleansing and shaping of canals, calcium hydroxide medicaments were applied and stored for different periods of time (1, 7, 30, 90 days). The root was horizontally sectioned into 2 mm thick specimens and the microhardness was measured using Vickers microhardness tester. The results were as follows : Root dentin microhardness of primary teeth decreased with long term exposure to calcium hydroxide medicaments according to the experimental period and showed statistically significance (p < 0.05). Root dentin microhardness of primary tooth filled with calcium hydroxide mixed with distilled water showed more decrease than filled with Vitapex and showed statistically significance (p < 0.05). Root dentin microhardness of a control group without exposure to calcium hydroxide decreased according to the experimental period and showed statistically significance (p < 0.05).

• Journal of the korean academy of Pediatric Dentistry
• /
• v.47 no.3
• /
• pp.320-326
• /
• 2020

The aim of this study was to compare compressive strength and microhardness of recently introduced alkasite restorative materials with glass ionomer cement and flowable composite resin. For each material, 20 samples were prepared respectively for compressive strength and Vickers microhardness test. The compressive strength was measured with universal testing machine at crosshead speed of 1 mm/min. And microhardness was measured using Vickers Micro hardness testing machine under 500 g load and 10 seconds dwelling time at 1 hour, 1 day, 7 days, 14 days, 21 days and 35 days. The compressive strength was highest in composite resin, followed by alkasite, and glass ionomer cement. In microhardness test, composite resin, which had no change throughout experimental periods, showed highest microhardness in 1 hour, 1 day, and 7 days measurement. The glass ionomer cement showed increase in microhardness for 7 days and no difference was found with composite resin after 14 days measurement. For alkasite, maximum microhardness was measured on 14 days, but showed gradual decrease.

• Korean Journal of Materials Research
• /
• v.10 no.5
• /
• pp.335-342
• /
• 2000

The microhardness of rhenium sheets was determined as a function of indentation load and temperature. The temperature dependence of the microhardness between room temperatures and $1000 ^{\circ}C$was studied using a hot microhardness tester equipped with a Vickers indenter. The load dependence of the microhardness was investigated using oth a Vickers and a Knoop indenter. The indentation size effect (ISE) was well explained using the normalized Meyers law. The hardness of the annealed rhenium sheet approached that of the as-rolled sheets at large indentation loads because of work-hardening under the indenter during indentation. The hardness at zero load(obtained from extrapolation of the load dependence of the hardness) suggested that the hardness is controlled by two different mech-anisms having different thermal activation. At low temperature the activation energy for the mechanism controlling the hardness was approximately 0.02 eV , Whereas at higher temperatures that was approximately 0.15eV. The tranisi-tion temperature between the two different controlling mechanisms was about $250^{\circ}C$.

• Restorative Dentistry and Endodontics
• /
• v.31 no.6
• /
• pp.470-476
• /
• 2006

The objective of this in situ study was to evaluate the effects of whitening strip (Claren, LG Household & Health Care Ltd, 2.6% hydrogen peroxide) and gel (Opalescence, Ultradent, 10% carbamide peroxide) on microhardness of enamel in comparison with untreated control. Extracted twenty human upper incisors were disinfected, cleaned, and labial side of each incisor sectioned into 3 fragments by 2 ${\times}$ 2 mm size. After sectioning, labial sides of fragments were flattened and fixed to orthodontic bracket using flowable composite resin. Specimens prepared from each tooth were attached to the labial side of upper incisors of twenty volunteers one by one and treated by three different methods: (1) untreated control (2) treated with whitening strip for 14 days (3) treated with whitening gel for 14 days. Microhardness (Microhardness tester, Zwick) of each specimen was measured at the baseline of pre-treatment, immediate after bleaching treatment, 14 days after bleaching treatment and Knoop Hardness Number was determined. Microhardness changes of experimental groups were compared. The results show that tooth whitening strip and gel used in this study does not effect the microhardness of enamel during bleaching procedure.

• Journal of the korean academy of Pediatric Dentistry
• /
• v.43 no.4
• /
• pp.427-434
• /
• 2016

The aim of this study was to compare the mechanical properties of high viscosity bulk-fill resin composites, $Filtek^{TM}$ Bulk Fill Posterior Restorative (FBF) and $Tetric^{(R)}$ N-Ceram Bulk Fill (TBF), with conventional composite ($Filtek^{TM}$ Z-350 XT, Z-350). The Vickers hardness test which indicates the degree of conversion was performed and the dye penetration test was performed to measure the microleakage which indicates polymerization shrinkage amount. To minimize experimental error, the standardized 3D-printed molds and the bovine teeth were used. Obtained data were analyzed by the Kruskal-Wallis test and Mann-Whitney test with the confidence interval of 95%. In the microhardness test within 1 hour of polymerization, lower surface of FBF and TBF showed significantly lower value than that of Z-350 (p < 0.05). But after 24 hours, the microhardness of FBF had increased and showed no significant difference with Z-350 (p > 0.05). In top and 2 mm depth surface, mean microhardness values were in the following order: Z-350 > FBF > TBF (p < 0.05). The mean microleakage value of TBF was significantly lower than others (p < 0.05). For clinical application of bulk-fill resin composites, caution for applying masticatory forces during 24 hours after polymerization is advised and further studies to decrease microleakage should be conducted.

• Restorative Dentistry and Endodontics
• /
• v.26 no.5
• /
• pp.363-371
• /
• 2001

심미성 수복재 중합시 사용되는 광원은 다양한 요인들에 의해 선택되어지고 있지만 이러한 요인들은 앞으로도 논란의 여지를 많이 남겨두고 있다. 또한 현재 사용되고 있는 중합법들이 제각기 독특한 장점들을 갖고 있기 때문에 최적의 중합법 결정이 필요한 시점이다. 이에 본 연구에서는 중합광의 강도(50, 100, 200, 300, 400, 600mW/$\textrm{cm}^2$)와 중합시간(10, 20, 40초)을 다양하게 변화시켰을 때 복합레진의 미세경도와 미세누출도가 어떠한 양태를 보이는지를 관찰하고자 하였다. 본 실험에서는 A3 색상의 혼합형 복합레진인 국산 DenFil과 미세입자형 복합레진인 Esthet X를 사용하였다. 중합 1일 후 복합레진의 Vickers 경도는 다이아몬드형 압흔 길이를 측정하여 평가하였으며 미세누출도는 1% methylene blue용액을 이용한 방법과 주사전자 현미경을 이용한 수복물과 치질간의 최대 이개도 평가법의 두 가지 방법으로 측정하였다. 본 연구의 결과는 다음과 같다; 1. 미세경도는 시편 상면이 하면에 비해 단단한 양태를 보였으며 상, 하면에 관계없이 혼합형 복합레진인 국산 DenFil이 미세입자형 복합레진인 Esthetx에 비해 높은 경도치를 보였다. 2. 모든 미세 경도 실험에서 너무 낮은 광도(50mW/$\textrm{cm}^2$, 100mW/$\textrm{cm}^2$)로 중합한 군에서는 대조군에 비해 유의하게 낮은 미세 경도를 보였다(p<0.05). 3. 상면의 경우, DenFil은 중합시간과 관계없이 200mW/$\textrm{cm}^2$ 이상의 광도에서 대조군(600mW/$\textrm{cm}^2$ 광도로 40초간 중합)과 유의차 없는 미세경도치를 보였으나, Esthet X는 200mW/$\textrm{cm}^2$ 이상의 광도로 40초 동안 중합한 군에서만 대조군과 유의차 없는 미세경도치를 보였다. 4. 하면의 경우 DenFil은 300mW/$\textrm{cm}^2$ 이상의 광도로, Esthet X는 200mW/$\textrm{cm}^2$ 이상의 광도로 각기 40초 동안 중합한 군에서만 대조군과 유의차 없는 미세경도치를 보였다. 5. 법랑질 변연부에서는 색소 침투가 전혀 없었으나 상아질 변연부에서는 정도의 차이는 있었지만 모든 시편에서 색소 침투를 보였다. 6. 통계적 유의차는 없었지만 저광도에서 우수한 미세누출도를 보였으며 색소 침투법과 최대 이개도 평가법간에는 상관성이 매우 낮았다 (p=0.801).

• Proceedings of the Korean Nuclear Society Conference
• /
• 1998.05b
• /
• pp.130-135
• /
• 1998

Zr합금의 재결정에 미치는 Sn, V, Sb의 영향을 조사하기 위해 2원계와 3원계로 구성된 12종의 Zr합금에 대하여 미세 조직 관찰 및 경도 측정을 실시하였다. 고진공 분위기의 여러 온도 조건에서 열처리된 시편의 미세조직을 편광광학현미경으로 관찰하였고 미소경도계로 경도값을 측정하였다. 미세조직 사진을 관찰한 결과 열처리 온도가 올라감에 따라 약 50$0^{\circ}C$ 까지는 가공조직을 그대로 유지하다가 첨가원소에 따라 다소 차이는 있었지만 55$0^{\circ}C$ ~ $700^{\circ}C$ 사이에서 재결정이 완료되었다. 재결정이 일어난 후에는 첨가원소의 첨가량이 적은 합금의 경우 결정립이 급격히 성장하는 모습을 보였다. 온도에 따른 경도값의 측정으로 재결정 거동을 확실히 핑가할 수 있었으며 경도값의 변화와 미세조직 변화는 일치하는 경향을 보였다. 이와 같이 첨가원소가 증가함에 따라 재결정이 늦어지고 결정립이 미세화 되는 것은 첨가원소의 대부분이 석출물로 형성되어 각 합금의 재결정과 결정립 성장을 억제하기 때문이라고 사료된다.

• Journal of the korean academy of Pediatric Dentistry
• /
• v.44 no.3
• /
• pp.335-340
• /
• 2017

Composite resin becomes an essential material in pediatric dentistry. However, incremental filling of composite resin to minimize the polymerization shrinkage takes time. To reduce the polymerization shrinkage, clinicians and researchers have focused on bulk-filling materials. Bulk-base composite resin is newly introduced as bulk-filling composite resin. The purpose of this study was to evaluate microhardness profile of bulk-base composite resin according to the depth of cure. A high flow bulk-base material and a low flow bulk-base material were used for experimental group, and a conventional composite resin was used for control group. Each group consist of 20 specimens, $3.5{\times}3.5{\times}5.0mm$ mold was used to make specimen. Specimens were sectioned at the 2 mm and the 3 mm depth with milling machine. Microhardness profile was measured at the surface, 2 mm depth, 3 mm depth, and 4 mm depth. Microhardness of control group showed statistically significant difference (p < 0.05) according to the polymerization depth. In contrast, experimental group showed no statistically significant difference, except between 0 mm and 4 mm at HFB, 0 mm and 2 mm, 0 mm and 3 mm at MFB. At the surface and the 2 mm depth, the control group showed higher microhardness than the experimental groups (p < 0.05). However, at the 4 mm depth, the experimental groups showed significantly higher microhardness (p < 0.05). The results from this study, the bulk-base composite resin showed higher microhardness at the 4 mm and lower microhardness at the surface and the 2 mm depth. Therefore, if bulk-base resin overcomes the mechanical weakness, it could be considered using in pediatric dentistry.

• Journal of the korean academy of Pediatric Dentistry
• /
• v.37 no.4
• /
• pp.438-444
• /
• 2010

Giomer is a recently developed light-cured resin-based material. This study compared compressive strength and microhardness of composite resin, giomer and compomer after 5000 times of thermocycling at $5^{\circ}C$ and $55^{\circ}C$. The following results were obtained. 1. Composite resin resulted in the highest compressive strengths both before and after thermocycling, followed by giomer and compomer. There were statistically significant differences between composite resin and giomer/compomer (p<0.05), but no statistically significant differences between giomer and compomer. 2. Both before and after thermocycling, microhardness values appeared in the order of composite resin, giomer and compomer with statistically significant differences in microhardness of composite resin, giomer and compomer (p<0.05). 3. After thermocycling, microhardness of composite resin, giomer and compomer decreased with a statistically significant difference (p<0.05). In conclusion, giomer demonstrates higher microhardness than compomer, but lower compressive strength and microhardness than composite resin. In addition, the decrease in microhardness and compressive strength after thermocycling proves the necessity for a thorough understanding in mechanical properties of restoration materials prior to their clinical application.

• Journal of the korean academy of Pediatric Dentistry
• /
• v.45 no.4
• /
• pp.418-425
• /
• 2018

This study was to measure and compare the amount of fluoride, microhardness and solubility of high viscosity glass ionomer and resin-reinforced glass ionomer during 84 days. Fuji IX GP EXTRA, Fuji IX GP, Fuji II LC and Filtek$^{TM}$ Z350XT stored in deionized water for 84 days to measure fluoride release, microhardness and solubility. As a result of measurement of fluoride release, all the glass ionomers showed the highest amount of fluoride release on day 1 and gradually decreased. Fuji IX GP EXTRA showed the highest amount of fluoride release and cumulative release. And Fuji IX GP and Fuji II LC showed no significant difference. Microhardness measurements showed that all experimental groups decreased 1 day after exposure to water. After 84 days, microhardness showed no significant difference between Fuji IX GP EXTRA and Fuji IX GP, and Fuji II LC was the lowest. In the solubility measurement, Fuji IX GP EXTRA, Fuji IX GP, and Fuji II LC increased rapidly to 21 days. After 21 days, there was no significant difference in the three groups. As a result, short term fluoride release affects solubility and microhardness, but long term fluoride release has no correlation. Through this study, the amount of fluoride, microhardness, and solubility of various glass ionomers were evaluated, and these properties could be applied clinically.