Denforus Co.

Seocho Gu, South Korea

Denforus Co.

Seocho Gu, South Korea

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Lee Y.-K.,Denforus Co. | Yu B.,Seoul National University | Zhao G.-F.,Seoul National University | Lim J.I.,Seoul National University
Dental Materials Journal | Year: 2010

Changes in the translucency, fluorescence, and opalescence of experimental 10-50% 2-hydroxyethyl methacrylate (HEMA)-added glass ionomers (HAGIs) after 5,000 cycles of thermocycling were determined and compared with those of commercial resin-modified glass ionomers (RMGIs). Changes in the translucency (TP), fluorescence (FL), and opalescence (OP) parameters were in the range of -3.5 to 0.2, -2.3 to 0.3 and -2.6 to 9.1 units respectively for HAGIs; and -0.9 to 0.3, -0.7 to 0.6, and 1.1 to 2.3 units respectively for RMGIs. Changes in the TP, FL, and OP of HAGIs were influenced by the HEMA content and powder shade, and were generally larger than those of RMGIs. Since the changes in TP, FL, and OP of experimental HAGIs were influenced by the HEMA content, there arises a need to determine the optimal HEMA ratio to attain high stability for these optical properties. In addition, results of this study showed that apart from optimal HEMA ratio, future studies should include other aspects and factors that contribute to age-dependent changes in optical properties.


Lim J.I.,Yonsei University | Lee Y.-K.,Denforus Co | Shin J.-S.,Yonsei University | Lim K.-J.,Yonsei University
Journal of Biomaterials Science, Polymer Edition | Year: 2011

For tissue-engineering applications, a 3D porous chitosan scaffold was simply prepared from a mixture of acidic chitosan solution and sodium acetate particles as the porogen by a salt-leaching method. Differences in the porous structure in terms of pore morphology and interconnectivity between the salt-leached chitosan scaffold and phase-separated scaffold as the control were examined by using scanning electron microscopy, protein release and enzymatic degradation tests. A fibroblast (NIH-3T3) cell culture was performed for cell affinity evaluation. The chitosan scaffold prepared by salt-leaching showed good interconnectivity and improved mechanical properties. Furthermore, the chitosan scaffolds showed a high initial cell adhesion after 4 h cell culture and increased cell proliferation than the control. Thus, salt-leached chitosan scaffolds can be used for various tissue-engineering applications. © Koninklijke Brill NV, Leiden, 2011.


Lim J.I.,Yonsei University | Lee Y.-K.,Denforus Co. | Shin J.-S.,Yonsei University | Lim K.-J.,Yonsei University | Lim K.-J.,ProteomeTech Inc.
Materials Letters | Year: 2010

To improve the mechanical properties such as flexibility and bond strength of cyanoacrylates, poly(l-lactide-co-ε-caprolactone) (PLCL) copolymers were dissolved into 2 kinds of cyanoacrylates, ethyl 2-cyanoacrylate (EC) and allyl 2-cyanoacrylate (AC). Mechanical properties such as bond strength, bending-stress recovery, and crystallization intensity were measured. The optimal concentration for high bond strength was determined to be 8% PLCL (molar ratio 70:30). EC/8% PLCL (70:30) exhibited three times higher bond strength as compared with that of EC. Further, AC/8% PLCL (50:50) exhibited better bending recovery than other materials. These results indicate that cyanoacrylate/PLCL materials can be widely used as adhesives in various fields. © 2010 Elsevier B.V. All rights reserved.


Lee Y.-K.,Denforus Co. | Yu B.,Kyung Hee University | Lee S.-H.,Denforus Co. | Cho M.-S.,Denforus Co. | And 2 more authors.
Dental Materials | Year: 2010

Objectives: Optical properties of an object are determined visually or instrumentally. Although instrumental measurement provides objective and quantitative color coordinates, these values vary by the measurement method such as specimen and background conditions, instrument settings and illuminant. The objective of this study was to review the influence of the measurement method on the instrumental color coordinates of esthetic dental restorative materials. Methods: Published reports on the measurement method dependent color variations of esthetic restorative materials were reviewed. Results: Surface roughness influences the color coordinates differently by the surface roughness range and the measurement geometry. Specimen thickness and the kind of illuminant influence the color coordinates, and the influence of background varied by specimen thickness. Therefore, the specular component excluded (SCE) geometry that reflects the surface condition of specimens is suggested as the correct measurement geometry. Surface roughness, thickness and layering of specimens, and the kind of illuminant should be stipulated in each measurement. There should be a standard for the color and gloss of the background. Significance: Variables in instrumental color measurements should be stipulated to obtain consistent and comparable color coordinates, and a general guideline for instrumental color measurement of dental materials should be established. © 2010 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.


Lee Y.-K.,Denforus Co. | Yu B.,Kyung Hee University | Lee S.-H.,Denforus Co. | Cho M.-S.,Denforus Co. | And 2 more authors.
Dental Materials | Year: 2010

Objectives: The objectives of this study were to review the shade compatibility of esthetic restorative materials and to provide a visual method to harmonize the color of them. Methods: Published reports on the color ranges and distributions of shade guides, color differences between restorative materials and the referenced shade guides, and those between the identical shade designated restorative materials were reviewed. Results: Several limitations in shade guides should be considered in color matching such as (1) color ranges and distributions of shade guides are different from those of human teeth, (2) arrangements of shade tabs in shade guides are not ideally logical, and (3) color of marketed esthetic restorative materials and the referenced shade tabs is significantly different. Color coordinates of restorative materials of the identical shade designations vary by the kind and brand of the restorative materials. Color differences between restorative materials and the referenced shade guides and those between the identical shade designated restorative materials are generally higher than perceptible limits. A visual color harmonization method was suggested, and the considerations for the instrumental color harmonization were provided. Significance: Visual color matching would result in color mismatching by the kind and brand of the restorative materials. The first step to improve the color matching performance would be the harmonization of the color of restorative materials with those of the corresponding shade tabs. © 2010 Academy of Dental Materials.


Lim J.I.,Yonsei University | Lim K.-J.,Yonsei University | Lim H.-N.,Kyung Hee University | Lee Y.-K.,Denforus Co.
Journal of Materials Science | Year: 2010

Glass ionomer cement (GIC) has been successfully used in dental field for more than 40 years. Despite numerous advantages of GIC, low bond strength and slow setting rate limited conventional GICs for use only at low stress-bearing areas. To improve bond strength to tooth, two kinds of cyanoacrylates such as ethyl 2-cyanoacrylate (EC) and allyl 2-cyanoacrylate (AC) were added in a commercial GIC. Changes in setting time of cyanoacrylate-modified GICs (CMGICs) according to the concentration of cyanoacrylates and/or p-toluene sulfonic acid (TSA) was investigated using a rheometer. Shear bond strength to human dentin was measured. Biocompatibility was determined by the viability of fibroblasts. Optimal concentrations for EC and TSA were 5-10% of the GIC powder and 30% of the GIC liquid, respectively. EC-based CMGIC showed twofold increase of initial bond strength compared with conventional GIC. Also, AC-based CMGIC showed three times higher bond strength and similar biocompatibility compared with the GIC. Therefore, CMGIC materials can be widely applied in dental adhesive restoration field because they showed improved bond strength and proper setting time. © 2010 Springer Science+Business Media, LLC.


Yu B.,Kyung Hee University | Zhao G.,Denforus Co. | Lim H.,Kyung Hee University | Lim J.,Denforus Co. | Lee Y.,Denforus Co.
Journal of Materials Science and Technology | Year: 2010

Color stability of dental resin modified glass ionomer (RMGI) has been a challenge to dentistry; therefore, systematic changes in 2-hydroxyethyl methacrylate (HEMA) content were performed experimentally to find an idea to enhance the color stability. Changes in color (ΔEab *) and color coordinates (ΔL*, Δa* and Δb*) of experimental 10-50 wt pct HEMA-added dental glass ionomers (HAGIs) and corresponding RMGIs were determined after 5000 cycles of thermocycling. Color changes of HAGIs were not influenced by the HEMA content while ΔL*, Δa * and Δb* values were influenced by the HEMA content. Color stability of 30% or 40% HEMA-added HAGIs was not different from those of the commercial RMGIs. Since the influence of HEMA itself on the color stability of HAGIs was limited, compositional modification to increase the color stability of these materials should be developed.


Lim H.-N.,Kyung Hee University | Yu B.,Kyung Hee University | Lim J.I.,Yonsei University | Lee Y.-K.,Denforus Co.
Dental Materials | Year: 2010

Objectives: Color coordinates of translucent esthetic materials measured by traditional spectrophotometers (SP) would deviate from those measured by newly introduced spectroradiometers (SR), which might simulate the clinical viewing condition better. This study aimed to determine the correlations in the SP- and SR-based color coordinates and color differences of all-ceramic materials. Methods: Specimens for seven A2 shade core ceramics (n = 7) and corresponding A2 and A3 shades veneer ceramics (n = 7) were fabricated in clinically relevant thicknesses (1.5 mm after layering). Color of layered specimens was measured according to the CIELAB color scale by a SP and a SR. Color differences (ΔEab) between the reference ceramics and the corresponding layered ceramics were calculated. Correlations between SP- and SR-based color coordinates and color difference values were determined (α = 0.05). Results: SR-based color coordinates were significantly different from the SP-based values; however, general shifting trends by the instrument were observed. SP- and SR-based CIE a*, b* and chroma values showed significant correlations (p < 0.05); however, the CIE L* values and the color differences with the reference showed no significant correlations (p > 0.05). Significance: The color coordinates representing the hue attribute (CIE a*, b* and chroma) measured by a spectrophotometer and a spectroradiometer showed significant correlations; however, the color coordinates and the color difference values were significantly different by the instrument. Therefore, color coordinates and the color difference values based on different instruments should not be compared directly. © 2010 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.


Yu B.,Kyung Hee University | Lim H.-N.,Kyung Hee University | Lee Y.-K.,Denforus Co.
Materials and Design | Year: 2010

This study determined the influence of nano- and micro-filler proportions on the stabilities of color, translucency and opalescence of experimental dental resin composites after wet thermocycling. Silane-coated nano- (mean: 40. nm) and micro-glass fillers (mean: 0.77 μm), in the ratios of 0:6 (N0M6), 1:5 (N1M5), 2:4 (N2M4), 3:3 (N3M3), 4:2 (N4M2), 5:1 (N5M1) and 6:0 (N6M0), were added to 1:1 mixed BisGMA and TEGDMA light curing resin matrix with a total content of 60. wt.% of the resin composites. Reflected and transmitted colors of cured specimens (1. mm in thickness) were measured before and after 5000 cycles of thermocycling with a spectrophotometer. A commercial dental resin composite with a filler content of 65. wt.% was used as a reference. As results, changes in color (ΔEab*), translucency (ΔTP) and opalescence (ΔOP) were in the range of 1.1-3.6, -4.5 to 0.1 and -3.7 to -0.7 units, respectively, all of which were influenced by the filler proportion (p<0.05). A hybrid composite (N4M2) and the nano-filled composite (N6M0) showed the smallest color change, while N4M2 alone showed the smallest translucency change (p<0.05). All the experimental composites showed significant changes in opalescence (p<0.05). Experimental hybrid composite containing 2:1 mixed nano- and micro- fillers showed the best stabilities in color and translucency. The micro-filled composite (N0M6) always showed higher translucency but lower opalescence than those of the hybrid and nano-filled composites. © 2010 Elsevier Ltd.


PubMed | Denforus Co
Type: Journal Article | Journal: The Journal of prosthetic dentistry | Year: 2010

The color attributes of commercially available shade guides have been measured by spectrophotometers (SP), which are designed to measure flat surfaces. However, there is limited information on the color distribution of shade guides as measured by spectroradiometers (SR), which are capable of measuring the color of curved surfaces.The purpose of this study was to determine the distributions of lightness (CIE L*) and chroma (C*(ab)) step intervals between adjacent shade tabs of a shade guide based on the lightness, chroma, and hue attributes measured by an SR.Lightness, chroma, hue angle, and CIE a* and b* values of the shade tabs (n=26) from a shade guide (Vitapan 3D-Master) were measured by an SR under daylight conditions. The distributions of the ratios in lightness and chroma of each tab compared with the lowest lightness tab or the lowest chroma tab were determined. The values for each color parameter were analyzed by a 3-way ANOVA with the factors of lightness, chroma, and hue designations of the shade tabs (alpha=.05).The chroma and CIE a* and b* values were influenced by the lightness, chroma, and hue designations of the shade tabs (P<.001); however, the lightness and hue angle were influenced by the lightness and hue designations, but not by the chroma designation. Distributions for the CIE a* and b* values, in each lightness group, corresponded with the chroma designation. However, the intervals in the lightness and chroma scales between adjacent tabs were not uniform.The intervals in the color parameters between adjacent shade tabs were not uniform based on SR measurements. Therefore, a shade guide in which shade tabs are more equally spaced by the color attributes, based on the values as measured by an SR along with observers responses with respect to the equality of the intervals, should be devised.

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