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Lee Y.-K.,Institute for Clinical Performance of Biomaterials ICPB
Journal of Biomedical Optics | Year: 2014

The objective was to determine whether there were significant correlations in the three color coordinates within each of two color coordinate systems, such as the Commission Internationale de l'Eclairage (CIE) L∗a∗bsystem, and the lightness, chroma, and hue angle system, of human vital teeth. The color of six maxillary and six mandibular anterior teeth was measured by the Shade Vision System. Pearson correlations between each pair of the color coordinates were determined (α= 0.01). The influence of two color coordinates on the other color coordinate was determined with a multiple regression analysis (α =0.01). Based on correlation analyses, all the color coordinate pairs showed significant correlations except for the chroma and hue angle pair. The CIE L∗was negatively correlated with the CIE a∗, b∗, and chroma, but positively correlated with the hue angle. The CIE a∗was positively correlated with the CIE b∗and chroma. Tooth color coordinates were correlated each other. Lighter teeth were less chromatic both in the CIE a∗and b∗coordinates. Therefore, it was postulated that the three color coordinates of human teeth were harmonized within certain color attribute ranges, and a lack of correlations in these coordinates might indicate external/internal discolorations and/or anomalies of teeth. © 2014 Society of Photo-Optical Instrumentation Engineers.

Lee Y.-K.,Institute for Clinical Performance of Biomaterials ICPB | Yu B.,CAS Institute of Process Engineering | Zhao G.-F.,W-Z Biotech, Llc | Lim J.I.,Dankook University
Journal of Esthetic and Restorative Dentistry | Year: 2015

Abstract Statement of Problem Color of esthetic restorative materials shifts toward color of adjacent material. Purpose The purposes were to determine the amount of distance-dependent color shift in resin composites toward the color of adjacent materials and to define a color shift parameter (CSP) that can quantify this phenomenon. Methods Three brands of resin composites, two shades for each, were investigated. Specimens of 2 (thickness) × 4 (width) × 16 (length) mm3 were fixed in an adjustable XY stage in contact with black and white ceramic tiles at each end. Color was measured by a spectroradiometer at seven separated points in 2-mm intervals, in which P1 was 2 mm away from the black tile. Mean value of the color differences (ΔE∗ab) between P1 and each of the other measurement points (P2-P6) was defined as the CSP, in which higher CSP value indicated smaller color assimilation toward P1 color. Results The range of the CSP was 7.5-12.4, which was influenced by the brand and shade of resin composites (p < 0.05). Conclusions The CSP defined in this study provided the amount of color shift of esthetic materials toward adjacent color, which indicated the color assimilation effect of these materials. Clinical Significance The CSP investigated in the present study might be used to compare the tendency of color assimilation of esthetic restorative materials, and proper CSP ranges for optimal color assimilation or color blocking should be further determined. © 2014 Wiley Periodicals, Inc.

Lee Y.-K.,Institute for Clinical Performance of Biomaterials ICPB
Materials | Year: 2015

Translucency of dental ceramics, esthetic posts and orthodontic brackets was reviewed. Translucency parameter (TP) and contrast ratio (CR) are generally used for translucency evaluation. For the evaluation of translucency, two criteria such as the translucency of human teeth (TP = 15-19, 1 mm thick) and the visual perceptibility threshold for the translucency difference (ΔCR > 0.07 or ΔTP > 2) were used. In ceramics, translucency differences were in the perceptible range depending on the type of material and the thickness. However, variations caused by the difference in the required thickness for each layer by the material and also by the measurement protocols should be considered. As to the translucency of esthetic posts, a significant difference was found among the post systems. Translucency was influenced by the bracket composition and brand, and the differences by the brand were visually perceptible. © 2015 by the authors.

Lee Y.-K.,Institute for Clinical Performance of Biomaterials ICPB | Cha H.-S.,University of Ulsan | Yu B.,CAS Institute of Process Engineering
Journal of Biomedical Optics | Year: 2014

The color of an object is perceived differently depending on the ambient light conditions. Since dental all-ceramic restorations are fabricated by building up several layers to reproduce the tooth shade, the optical properties of each layer should be optimized for successful shade reproduction. This study aimed to determine the separate contributions of the color shifts in each of the core and veneer layers of all-ceramics by switching the illuminating lights on the color shifts of layered ceramics. Specimens of seven kinds of core ceramics and the corresponding veneer ceramics for each core were fabricated with a layered thickness of 1.5 mm. A sintering ceramic was used as a reference core material. The Commission Internationale de l'Eclairage (CIE) color coordinates of core, veneer, and layered specimens were measured with a spectroradiometer under the CIE illuminant D65 (daylight), A (incandescent lamp), and F9 (fluorescent lamp) simulating lights. Color shifts of the layered specimens were primarily determined by the CIE a∗ shifts (D65 to A switch) or by the CIE b∗ shifts (D65 to F9 switch) of the veneer layer. The color coordinates shifts in the constituent layers differentially influenced those of the layered specimens by the kind of switched lights. Therefore, the optical properties of the constituent layers of all-ceramics should be controlled to reflect these findings. © 2014 Society of Photo-Optical Instrumentation Engineers (SPIE).

Lee Y.-K.,Institute for Clinical Performance of Biomaterials ICPB
Journal of Biomedical Optics | Year: 2015

Fluorescent emission of human teeth and dental calculus is important for the esthetic rehabilitation of teeth, diagnosis of dental caries, and detection of dental calculus. The purposes of this review were to summarize the fluorescence and phosphorescence of human teeth by ambient ultraviolet (UV) light, to investigate the clinically relevant fluorescence measurement methods in dentistry, and to review the fluorescence of teeth and dental calculus by specific wavelength light. Dentine was three times more phosphorescent than enamel. When exposed to light sources containing UV components, the fluorescence of human teeth gives them the quality of vitality, and fluorescent emission with a peak of 440 nm is observed. Esthetic restorative materials should have fluorescence properties similar to those of natural teeth. Based on the fluorescence of teeth and restorative materials as determined with a spectrophotometer, a fluorescence parameter was defined. As to the fluorescence spectra by a specific wavelength, varied wavelengths were investigated for clinical applications, and several methods for the diagnosis of dental caries and the detection of dental calculus were developed. Since fluorescent properties of dental hard tissues have been used and would be expanded in diverse fields of clinical practice, these properties should be investigated further, embracing newly developed optical techniques. © 2015 Society of Photo-Optical Instrumentation Engineers.

Yu B.,CAS Institute of Process Engineering | Zhao G.-F.,Institute for Clinical Performance of Biomaterials ICPB | Lim J.I.,Kyung Hee University | Lee Y.-K.,Institute for Clinical Performance of Biomaterials ICPB
Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine | Year: 2011

Bone tissue functions in varied mechanical systems of the body under static and dynamic conditions. Therefore, it is essential to understand the mechanical responses of bone at varied loading rates, especially those at fast loading rates. This study has investigated the effect of loading rate on the compressive mechanical properties of bovine cortical bone. Bone specimens of 3.85 mm in diameter and 7.7 mm in length were compressed longitudinally with the loading rates of 2 to 2000 mm/s (corresponding strain rates of 0.26 to 260 s -1). As a result, bovine cortical bone showed high linear elasticity when the loading rate was slow, and exhibited three definite regions of linear elasticity, plastic deformation, and densification at faster loading rates. The elastic modulus showed no dependency on the loading rate. Compressive strength, strain at fracture, and toughness increased as the loading rate increased under the condition that the loading rates were slower than each critical loading rate of 1000, 100, and 1500 mm/s, respectively. However, all showed no significant changes when the loading rates were faster than the corresponding critical loading rates. In conclusion, as the loading rate increased, changes in the compressive mechanical parameters were different depending on the parameter and the loading rate range. Compressive mechanical behaviour of bovine cortical bone showed a brittle nature under high strain rates (strain rates > 13 s -1). These findings should be reflected in the biomimetic simulation of biomaterials for bone tissue repair and engineering. © IMechE 2011.

Lee Y.-K.,Institute for Clinical Performance of Biomaterials ICPB | Zhao G.-F.,Institute for Clinical Performance of Biomaterials ICPB | Yu B.,Kyung Hee University | Lim H.-N.,Kyung Hee University | Lu H.,University of Houston
Color Research and Application | Year: 2012

This study measured the goniochromatic properties of human tooth dentin through the viewing angle dependent color change measurement, and determined the influence of the microscopic structural nonuniformity of dentin surface on the gonioappearance. Color of 21 polished dentin specimens was measured by a spectroradiometer in wet and dry conditions. Spectral reflectance values were obtained with 0, 20, 45, and 70° aspecular viewing angles to the surface. These values were converted to CIE color coordinates (CIE L*, a*, and b*) relative to the specular set (0°) standard white tile to determine general goniochromatic effect, and to the same aspecular set standard white tiles to determine the influence of nonuniformity on dentin surface caused by dentinal tubules. Color coordinates and chroma were influenced by the viewing angle (P < 0.05). As to the influence of nonuniformity, CIE L* and a* and chroma were influenced by the viewing angle while CIE b* was not (P = 0.05). Goniochromatic effect of human dentin was confirmed instrumentally, and the nonuniformity of dentin increased goniochromatic effect. Based on these results, goniochromatic properties of intact teeth should be studied further, and restorative materials that can simulate these properties should be developed. © 2011 Wiley Periodicals, Inc.

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