• Journal of the korean academy of Pediatric Dentistry
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• v.44 no.3
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• pp.306-316
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• 2017

The purpose of this study was to evaluate the effects of exposure to various children's drinks on the color stability of anterior primary teeth and different esthetic restorative materials clinically used in pediatric dentistry. Exfoliated maxillary primary central incisors that had been unaffected by caries were chosen as control group. Maxillary primary central incisor-shaped specimens made of strip crown and Nu-smile zirconia crowns were chosen as test groups. Polished strip resin crowns were additionally prepared to compare with unpolished strip resin crown. Each specimen and teeth were divided into 4 groups in which the test samples (n=5 each) were immersed in 4 different drinks (distilled water, cola, grape juice, jelly juice) for 6 days. In all 4 drink groups, all specimens generally showed increasing ${\Delta}E^*$ value (color difference) with time. Polished resin strip crown had higher ${\Delta}E^*$ value than the unpolished in cola, grape juice and jelly juice groups. ${\Delta}E^*$ value of zirconia crown in cola, grape juice and jelly juice groups were significantly different (p < 0.05). In conclusion, dietary control of children's drinks is required for preventing discoloration of restorative materials.

• Analytical Science and Technology
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• v.8 no.4
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• pp.793-798
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• 1995

A new chromoionophore sym-(decyl)(2-hydroxy-5-nitrobenzyloxy)-dibenzo-16-crown-5 (1) has been synthesized for $Na^+$ photometry in aqueous media. Apparent $pK_a$ values of 1 in the presence of 0.10 M LiCl, NaCl, and KCl were measured by spectrophotometry in 50% 1,4-dioxane-50% water (v/v) and compared with the $pK_a$ of 8.68 in the presence of 0.10 M TMACl. A significant $pK_a$ shift to a lower pH was only observed for $Na^+$ (${\Delta}pH=1.31$) due to selective binding of 1 with $Na^+$. Based upon this $pK_a$ shift, chromoionophore 1 was found to selectively respond to $Na^+$ with a detection limit of $10^{-3}M$ and no interference from $K^+$ up to 0.05 M for detection of 10.0 mM $Na^+$ in 50% 1,4-dioxane-50% water (v/v).

• Journal of the Korean Chemical Society
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• v.35 no.3
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• pp.288-291
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• 1991

• Journal of Technologic Dentistry
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• v.14 no.1
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• pp.95-118
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• 1992

Glass ceramics for crown were prepared by adding 3$\sim$11 wt% TiO2 to the weight percent composition of 34.7 CaO, 27.8 SiO2, 18.3P2O5, 12.6MgO and 6.6 TiO2. The starting glasses were prepared by melting the powdered batch in alumina crucible at 1350$\sim$1400 for 1 hr and then quenching into a distilled water. The nucleation and crystallization of the crystalline glass ceramics for crown were studied by DTA, SME and X-ray diffraction analysis. Frit containing 9.11 wt% TiO2 had crystallization temperature of 850$\sim$1075 and major crystalline phase was identified by X-ray diffraction as diopside(CaO-MgO-2SiO2). Activation energies for the crystallization processes were obtained from DTA by varing rates for the fits, and were calculated from modified Ozawa and Kissinger equations. Activation energy for the crystallization processes of the S-4 frit was 489.6 KJ/mol.

• Journal of the Korean Chemical Society
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• v.31 no.3
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• pp.250-257
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• 1987

The electrical conductances for the thorium (IV) complexes with crown ethers have been measured in DMSO, and water solvents, and the oxidation-reduction reaction mechanisms, electron number and diffusion coefficients in the reversible reduction process have been examined by polarography and cyclic voltammography. The dissociation mole ratio of $Th^{4+}$ and nitrate ion are 1:1 and in aprotic solvent, and 1:4 in protic solvent like as water. The limiting molar conductances of all complexes in aprotic solvent have been found to be in the range of $92.2{\times}159$ $ohm^{-1}cm^2mol^{-1}$. In aprotic solvent, DMSO, the reduction of each complex is reversible by one electron reduction of one step, and the range of diffusion coefficients is obserbed to be $5.83\;10^{-6}{\sim}6.90{\times}10^{-6}$. The complexes which have reduction step were hydrolyzed above at 1.8volt with reference saturated calomel electrode, generating the hydrogen gas. The reaction mechanisms of thorium (IV)-crown ether complexes appear as follows. ${Th_m(IV)L_n(H_2O)_x(NO_3)_{4y}}_=^{DMSO} {\overline{{Th_m(IV)L_n(H_2O)_x(NO_3)_{4y-1}}}^+ + NO_3-$

• Journal of the Korean Chemical Society
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• v.27 no.4
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• pp.262-267
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• 1983

A study has been carried out for a scheme of the selective extraction and determination of cesium, sodium and nuclides by the ion association with dicyclohexyl-24-crown-8 and sodium tetraphenylborate from primary coolant of a pressurized water reactor. For that purpose, the effects of hydrogen, cesium and borate ions on the extraction have been investigated. Interferences of iodine and xenon nuclides were found but could be removed by reducing with sodium thiosulfate and back extraction with 1 N hydrochloric acid solution, respectively.

• Korean Journal of Food Science and Technology
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• v.40 no.2
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• pp.171-177
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• 2008

The effects of hydrocooling and packaging type on the quality attributes of fresh-cut crown daisies (Chrysanthemum coronarium var. spatiosum) were investigated by examining weight loss, respiration, vitamin C content, total chlorophyll content, microbial load, and sensory properties during storage at 4 and 10$^{\circ}C$. Fresh crown daisies were trimmed and washed with cold water (1 and 5$^{\circ}C$) as well as tap water (10$^{\circ}C$) 3 times each for 30 sec. They were then packaged in PP (polypropylene) film bags or PETE (polyethylene terephthalate) trays, and stored for 9 days at 4 and 10$^{\circ}C$, respectively. In general, weight loss was reduced as a result of the washing and packaging. The respiration rate increased slowly during storage at 4$^{\circ}C$, and the vitamin C and total chlorophyll contents of the crown daisies packaged in PETE trays decreased gradually during storage. Finally, the treatments consisting of hydrocooling and then packaging in PETE trays resulted in approximately 1-2 log CFU/g reductions in microbial load.

• Applied Chemistry for Engineering
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• v.21 no.2
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• pp.142-147
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• 2010

Cryptand resins have been synthesized from 1-aza-18-crown-6 macrocyclic ligand attached to styrene (2th petroleum in 4th class hazardous materials) divinylbenzene copolymer with crosslinkage of 1%, 2%, 10%, and 18% by substitution reaction. The synthesis of these resins was confirmed by the content of chlorine, element analysis, surface area (BET), and IR-spectroscopy. The effects of pH, time and crosslinkage on adsorption of metal ion from water fire extinguishing agentby synthetic resin adsorbent were investigated. Metal ions showed a great adsorption over pH 3 and adsorption equilibriumof metal ions was about two hours. The adsorption selectivity determined in water was in the increasing order of sodium ($Na^{1+}$) > zinc ($Zn^{2+}$) > chromium ($Cr^{3+}$) ion. The adsorption was in the order of 1%, 2%, 10%, and 18% crosslinkage resin.

• The Journal of Korean Academy of Prosthodontics
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• v.43 no.6
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• pp.717-726
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• 2005

Statement of problem. One of the common problems of provisional crown and fixed partial denture materials is that when they are subjected to constant loads for a long period of time, they exhibit a dimensional change (creep). Purpose. The aim of this study was to investigate the viscoelastic behaviour of polymer-based provisional crown and fixed partial denture materials with time at constant compressive load. Material and methods. Three dimethacrylate-based materials (Protemp 3 Garant, Temphase, Luxatemp) and one monomethacrylate-based material (Trim) were selected. Dimensional changes of the specimens were recorded by a LVDT to evaluate their viscoelastic behavior and creep strain. For all specimens, two loading procedures were used. At first, static compressive stress of 4 MPa was applied for 30 minutes and followed by 1 hour of strain recovery. Then, after 24 hours of water storage, the specimens were loaded again. The creep values between materials were statistically analyzed using one-way ANOVA and multiple comparison $Scheff\acute{e}$ test. Independent samples t-test was also used to identify the difference of creep strain between first and secondary loading conditions at the significance level of 0.05. Results. Following application of the first loading, Trim showed the highest maximum creep strain (32.7%) followed by Luxatemp, Protemp 3 Garant and Temphase, with values of 3.78%, 2.86% and 1.77%, respectively. Trim was significantly different from other materials (P<0.05), while there were no significant differences among Luxatemp, Protemp 3 Garant and Temphase (P>0.05). The highest recovery and permanent set of Trim, were significantly different from those of others (P<0.05). At the secondary loading of the dimethacrylate-based materials, creep deformation, recovery and permanent set decreased and the percentage of recovery increased, while in Trim, all values of the measurements increased. This result showed that the secondary loading at 24 hours produced a significant creep magnitude. Conclusion. The dimethacrylate-based provisional crown and fixed partial denture materials showed significantly higher creep resistance and lower deformation than the monomethacrylate-based material. Thus, monomethacrylate-based materials should not be used in long-term stress-bearing situations.

• Journal of Dental Rehabilitation and Applied Science
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• v.18 no.3
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• pp.205-215
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• 2002

This study investigated the compressive fracture strength of Targis ceromer crown by the difference of occlusal thickness on a maxillary first premolar. Control group was a castable IPS-Empress all-ceramic crown with occlusal thickness of 1.5 mm constructed by layered technique. Experimental groups were Targis crowns having different occlusal thicknesses of 1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm, respectively. The classification of Targis group is T10, T15, T20, T25 and T15N (for no-thermocycling and occlusal thickness of 1.5mm). Ten samples were tested per each group. Except occlusal thickness, all dimension of metal die is same with axial inclination of $10^{\circ}$and marginal width 0.8mm chamfer. All crowns were cemented with Panavia F and thermocycled 1,000 times between $5^{\circ}$ and $55^{\circ}$ water bath with 10 sec dwelling time and 10 sec resting time. The compressive fracture strength was measured by universal testing machine. The results were as follows : 1. Fracture strength was increased as the occlusal thickness increased : compressive fracture strength of Group T10, T15, T20, T25 was $66.65{\pm}4.88kgf$, $75.04{\pm}3.01kgf$, $87.07{\pm}7.06kgf$ and $105.03{\pm}10.56kgf$, respectively. 2. When comparing material, Targis crown had higher fracture strength than IPS-Empress crown : the mean compressive strength of group T15 was $75.04{\pm}3.01kgf$ and the value of group Control was $37.66{\pm}4.28kgf$. 3. Fracture strength was decreased by thermocycling : the compressive fracture strength of T15 was $75.04{\pm}3.01kgf$, which is lower than $90.69{\pm}6.88kgf$ of group T15N. 4. The fracture line of crowns began at the loading point and extended along long axis of tooth. IPS-Empress showed adhesive failure pattern whereas Targis had adhesive and cohesive failure. In the SEM view, stress was distributed radially from loading point and the crack line was more prominent on Targis crown.