• The Journal of Advanced Prosthodontics
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• 제13권4호
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• pp.246-257
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• 2021

PURPOSE. This study aimed to investigate the Vickers Hardness Number (VHN) of light- and dual cured resin cements cured through monolithic zirconia specimens (VITA YZ) of various translucencies: translucent (T); high translucent (HT); super translucent (ST); and extra translucent (XT) at 0, 24, and 48 h after curing. MATERIALS AND METHODS. Four zirconia specimens from each translucency were prepared. Two light-cured resin cements (Variolink N LC; VL and RelyX Veneer; RL) and two dual-cured resin cements (Variolink N DC; VD and RelyX U200; RD) were used. The cement was mixed and loaded in a mold and cured for 20 s through the zirconia specimen. The upper surface of cements was tested for VHN using a microhardness tester at 0, 24, and 48 h after curing. The VHN were analyzed using two-way repeated, Brown-Forsythe ANOVA with Games Howell post-hoc analysis and independent t-tests (P < .05). RESULTS. All cements showed significantly higher VHN from 0 h to 24 h (P < .001). At 48 h, the VHN of light-cured cements were significantly lower when cured under the T groups than under XT groups (P = .001 in VL, P = .014 in RL). At each post curing time of each translucency, VD showed higher VHN than VL (P < .05), and RD also showed higher VHN than RL (P < .05). CONCLUSION. The translucency of zirconia has an effect on the VHN for light-cured resin cements, but has no effect on dual-cured resin cements. Dual-cured resin cement exhibited higher VHN than the light-cured resin cement from the same manufacturer. All resin cements showed significantly higher VHN from 0 h to 24 h.

• Advances in nano research
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• 제15권4호
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• pp.315-328
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• 2023

The main goal of the present study was to assess the effects of eggshell powder (ESP) and halloysite nanotubes (HNTs) on the mechanical properties of abaca fiber (AF)-reinforced natural composites. For this purpose, a limited number of indentation tests were first performed on the AF/polypropylene (PP) composites for different HNT and ESP loadings (0 wt.% ~ 6 wt.%), load amplitudes (150, 200, and 250 N), and two types of indenters (Vickers or conical). The Young's modulus, hardness and plasticity index of each specimen were calculated using the indentation test results and Oliver-Pharr method. The accuracy of the experimental results was confirmed by comparing the values of the Young's modulus obtained from the indentation test with the results of the conventional tensile test. Then, a feed-forward shallow artificial neural network (ANN) with high efficiency was trained based on the obtained experimental data. The trained ANN could properly predict the variations of the mentioned mechanical properties of AF/PP composites incorporated with different HNT and ESP loadings. Furthermore, the trained ANN demonstrated that HNTs increase the elastic modulus and hardness of the composite, while the incorporation of ESP reduces these properties. For instance, the Young's modulus of composites incorporated with 3 wt.% of ESP decreased by 30.7% compared with the pure composite, while increasing the weight fraction of ESP up to 6% decreased the Young's modulus by 34.8%. Moreover, the trained ANN indicated that HNTs have a more significant effect on reducing the plasticity index than ESP.

• 치위생과학회지
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• 제23권1호
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• pp.29-38
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• 2023

Background: The purpose of this study was to investigate the effect of salad dressings on the flowable composite resin surface and the erosion-inhibitory effect of calcium. Methods: The experiment included six groups: oriental dressing, balsamic dressing, lemon-garlic dressing, lemon-garlic dressing supplemented with 3% calcium, mineral water as a negative control group, and orange juice as a positive control group. pH and titratable acidity were measured. The prepared specimens were immersed in the experimental solutions for 1, 3, 5, 15, and 30 minutes. The surface microhardness was measured using the Vickers hardness number before and after the treatment, and the surface of the specimens was observed using a scanning electron microscope (SEM). Results: The pH values of the experimental groups in increasing order were as follows: lemon-garlic dressing (2.49±0.03), balsamic dressing (3.12±0.06), lemon-garlic dressing +3% calcium (3.27±0.09), oriental dressing (3.75±0.03), orange juice (3.82±0.02), and mineral water (7.32±0.16). The largest surface hardness reduction value was shown in lemon-garlic dressing (-9.61±1.16), followed by balsamic dressing (-9.17±1.63), oriental dressing (-8.62±1.09), orange juice (-8.19±1.36), lemon-garlic dressing +3% calcium (-6.76±1.23), and mineral water (-1.63±2.47). According to the SEM findings, the experimental and positive control groups showed rough surfaces and micropores, whereas the negative control group showed a smooth surface. Moreover, the lemon-garlic dressing with +3% calcium showed fewer micropores and a smoother surface than the lemon-garlic dressing. Conclusion: The intake of salad dressings at a low pH could weaken the surface microhardness of the flowable composite resin. However, adding calcium to these salad dressings can reduce the risk of microhardness reduction on the flowable composite resin surface.

• 대한소아치과학회지
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• 제44권4호
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• pp.412-418
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• 2017

브라켓 주위에 발생되는 법랑질 탈회는 교정 치료 시 극복해야 할 문제 중 하나이다. 본 연구는 교정용 브라켓 부착 시 사용되는 접착제 중 불소를 함유하는 교정용 프라이머의 적용이 법랑질 탈회 예방 및 재광화 유도에 미치는 효과를 알아보고자 시행되었다. 건전한 표면을 가진 발치 된 소의 절치 50개를 실험재료로 하여 법랑질 처리 방법에 따라 3개 군으로 분류하였다: (I) 아무처리하지 않은 시편, (II) 불소를 함유한 교정용 프라이머인 Light Bond$^{TM}$로 처리한 시편, (III) 전통적으로 불소를 함유하지 않는 프라이머인 Transbond$^{TM}$ XT Primer로 처리한 시편. 각 군을 인공우식용액에서 탈회시킨 다음 Q-ray view로 관찰하고, 비커스 표면미세경도 측정 및 편광현미경을 이용하여 우식 양상을 평가하였다. 인공 탈회 후 프라이머는 치아 표면에서 떨어져 나가 35 - 50% 잔존하는 것으로 보인다. 표면미세경도는 Light Bond$^{TM}$를 직접 적용한 법랑질 표면에서 가장 높았으나 유의한 차이는 없었다. 하지만 Light Bond$^{TM}$를 적용한 인접부위의 법랑질 표면미세경도는 아무처리를 하지 않은 대조군보다 유의하게 높은 값을 보였다. 편광현미경을 통해 관찰한 소견으로 Light Bond$^{TM}$를 직접 적용한 법랑질 표면은 탈회가 거의 나타나지 않았으며, Light Bond$^{TM}$의 인접부위에서는 가장 얕은 우식 양상과 재광화 소견을 보였다. 이상의 연구결과, 교정치료 시 법랑질 탈회의 발생을 줄이기 위해서 브라켓 부착 시 불소를 함유하는 프라이머의 사용이 유용함을 시사하는 바이다.

• 한국치위생학회지
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• 제10권5호
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• pp.947-953
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• 2010

Objectives : The purpose of this investigation was to evaluate the remineralization and acid resistance in fluoride varnish by Micro-computed tomography (micro CT). Methods : Specimens of bovine teeth enamel were embedded in resin, polished and randomly divided into 3 groups (a control group, a NaF solution group, a fluoride varnish group). Each group has 3 specimens that was standardized according to Vickers hardness number (VHN). Specimens were immersed in demineralization solution for 72 hours. The control group had no treatment, the NaF solution group was treated by a 5% NaF solution for 4 minutes, and the fluoride varnish group was treated by a fluoride varnish for one hour. All specimens were subjected to a chemical pH cycling method for 14 days. After a chemical pH cycling method, the density were measured using micro CT. Then, specimens were immersed in each demineralization solution for 72 hours. After demineralization processed, the density were measured using micro CT. Results : 1. The density was significantly higher in the fluoride varnish and 5% NaF solution group than that of the control group after 14 days cycling (p<0.05). And the density value of the fluoride varnish group was higher than that of the 5% NaF solution, with no significant difference. 2. The differences of density after acid resistance treatment were statistically significant among 3 groups(p<0.05). Conclusions : It is suggested that fluoride varnish showed the remineralizing effect and acid resistance effect on the enamel, and micro CT could be used to evaluate the change of enamel lesion.

• 한국치위생학회지
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• 제16권1호
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• pp.77-83
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• 2016

Objectives: This study was carried out to investigate the effect of fluoride application after dental prophylaxis by the type of dental floss. Methods: Artificial caries lesion was made on the surface of cow's permanent teeth having sound enamel surface and vickers hardness number(VHN) was measured. Specimens were classified into APF gel group and artificial saliva group. Each group was divided into waxed floss group and unwaxed flossed group. All specimens were immersed into the artificial saliva for one minute and dental flossing was applied to waxed or unwaxed floss. After washing and drying, APF gel groups were applied with fluoride for four minutes and artificial saliva groups were immersed into the artificial saliva for four minutes. After treatment, specimens were measured by VHN and surface conditions of enamel were confirmed by scanning electron microscopy(SEM). Results: VHN of waxed flossing and fluoride application group increased to $6.78{\pm}2.75$. VHN of unwaxed flossing and fluoride application group increased to $7.36{\pm}2.51$. There was no significant difference between waxed and unwaxed groups(p>0.05). VHN of waxed flossing and artificial saliva group increased to $1.07{\pm}2.84$. VHN of waxed flossing and artificial saliva group increased to $1.05{\pm}3.13$. There was no significant difference between waxed and unwaxed groups(p>0.05). There was significant increase in VHN between waxed/unwaxed flossing and fluoride application. However, waxed/unwaxed flossing with artificial saliva showed no significant VHN increase. SEM demonstrated no residue on the enamel surface in the waxed flossing groups. Conclusions: No difference was found in the remineralization of enamel by waxed flossing or unwaxed flossing.

• 대한기계학회논문집A
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• 제29권10호
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• pp.1407-1415
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• 2005

Strength change of an over-aged A12024 material was studied after being subjected to stages of severe plastic deformation by ECAP (Equal Channel Angular Pressing). Various kinds of strength value were measured using the conventional tensile test, Rockwell and Vickers hardness and the SP (small punch) test Due to limitation of the specimen size, tension test in transverse direction could not be conducted. Hence, SP test was employed for assessing the strength in transverse direction. Based on TEM observation the measured strength characteristics were explained based on the relation between microstructure, dislocation and strength. As the number of ECAP pass increases, the strength of A12024 was also increased. However, considerable change of strength, which is generally predicted, was not observed in this study. For the strength in transverse direction even decrease of the strength was observed after 6 passes of ECAP. It was argued that this decrease was due to dynamic recovery of dislocation density during or after ECAP processes at $150^{\circ}C$. The strength assessment equation proposed by the authors in the previous paper was shown to be very accurate. This argument was supported by comparing the results of conventional tensile test with those of SP test. It was also pointed that the Rockwell har(3ness value seemed to be able to represent the strength in the transverse direction.

• Restorative Dentistry and Endodontics
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• 제45권2호
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• pp.13.1-13.10
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• 2020

Objective: The aim of this study was to evaluate the influence of different modeling agents on the surface microhardness (Vickers hardness number; VHN), roughness (Ra), and color change (ΔE) of a nano-hybrid composite with or without exposure to discoloration by coffee. Materials and Methods: Sixty-four cylinder-shaped nano-hybrid composite specimens were prepared using a Teflon mold. The specimens' surfaces were prepared according to the following groups: group 1, no modeling agent; group 2, Modeling Liquid; group 3, a universal adhesive (G-Premio Bond); and group 4, the first step of a 2-step self-adhesive system (OptiBond XTR). Specimens were randomly allocated into 2 groups (n = 8) according to the storage medium (distilled water or coffee). VHN, Ra, and ΔE were measured at 24 hours, 1 week, and 6 weeks. The Kruskal-Wallis test followed by the Bonferroni correction for pairwise comparisons was used for statistical analysis (α = 0.05). Results: Storage time did not influence the VHN of the nano-hybrid composite in any group (p > 0.05). OptiBond XTR Primer application affected the VHN negatively in all investigated storage medium and time conditions (p < 0.05). Modeling Liquid application yielded improved Ra values for the specimens stored in coffee at each time point (p < 0.05). Modeling Liquid application was associated with the lowest ΔE values in all investigated storage medium and time conditions (p < 0.05). Conclusion: Different types of modeling agents could affect the surface properties and discoloration of nano-hybrid composites.

• 비파괴검사학회지
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• 제22권1호
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• pp.65-73
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• 2002

2.25Cr-1M 강이 $540^{\circ}C$에서 장시간 노출되었을 때 일어나는 미세조직 변화를 모사하기 위해 인공 열화를 실시하였으며 이에 대해 미세조직(탄환화물의 평균등가크기 및 단위면 개수), 기계적 성질 (인장강도 및 경도), 자기적 성질(보자력 및 잔류자화)을 측정하였다. 이들 결과를 비교함으로써 열화에 따른 자기적 성질의 변화와 미세조직 사이의 상관관계률 규명하였다. 탄화물을 그 형장에 따라 막대상, 구상, 침상으로 분류하였으며 침상의 탄화물은 열화 초반부에 급격히 소멸되는 경향을 보였다. 또한 보자력과 잔류자화는 열화 초반부에 급격히 감소한 후 점차 완만히 감소하는 경향을 보였다. 기계적 성질과 보자력 및 잔류자화 사이에는 선형적 상관관계가 존재하였다.

• Restorative Dentistry and Endodontics
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• 제39권4호
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• pp.310-318
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• 2014

Objectives: This study examined the influence of the resin thickness on the polymerization of silorane- and methacrylate-based composites. Materials and Methods: One silorane-based (Filtek P90, 3M ESPE) and two methacrylate-based (Filtek Z250 and Z350, 3M ESPE) composite resins were used. The number of photons were detected using a photodiode detector at the different thicknesses (thickness, 1, 2 and 3 mm) specimens. The microhardness of the top and bottom surfaces was measured (n = 15) using a Vickers hardness with 200 gf load and 15 sec dwell time conditions. The degree of conversion (DC) of the specimens was determined using Fourier transform infrared spectroscopy (FTIR). Scratched powder of each top and bottom surface of the specimen dissolved in ethanol for transmission FTIR spectroscopy. The refractive index was measured using a Abbe-type refractometer. To measure the polymerization shrinkage, a linometer was used. The results were analyzed using two-way ANOVA and Tukey's test at p < 0.05 level. Results: The silorane-based resin composite showed the lowest filler content and light attenuation among the specimens. P90 showed the highest values in the DC and the lowest microhardness at all depth. In the polymerization shrinkage, P90 showed a significantly lower shrinkage than the rest two resin products (p < 0.05). P90 showed a significantly lower refractive index than the remaining two resin products (p < 0.05). Conclusions: DC, microhardness, polymerization rate and refractive index linearly decreased as specimen thickness linearly increased. P90 showed much less polymerization shrinkage compared to other specimens. P90, even though achieved the highest DC, showed the lowest microhardness and refractive index.