Yong-Keun Lee

Measurement of translucency of tooth enamel and dentin

Objective. To determine the translucency of human and bovine enamel and dentin using reflection spectrophotometers. Material and Methods. The color of intact human and bovine enamel and dentin specimens was measured over a white and a black plasticine backing using two spectrophotometers with different aperture sizes; translucency parameter (TP) and contrast ratio (CR) were calculated. Plasticine was used as backing because the specimens were not uniform. The TP values of five composite resins measured over the backings of plasticine and reflectance standards were also determined. Results. There were no significant differences between the TP values of the composite resins measured over the backings of plasticine and reflectance standards (p>0.05). Mean TP values of 1 mm thick bovine enamel, bovine dentin, human enamel and human dentin were 14.7, 15.2, 18.7, and 16.4, respectively, based on the 3 mm round aperture. There were significant correlations between the TP values measured by the two apertures; the bigger the aperture size, the higher the TP value (r=0.87–0.91, p<0.01). The translucency of enamel and dentin increased in direct proportion to wavelength and in inverse proportion to thickness (r=0.87–0.91). Mean CR values were negatively correlated with the TP values (r = −0.93 to −0.78). Conclusions. These data could be used as references in the development of esthetic restorative materials and clinical shade-matching.

Spectroradiometric and spectrophotometric translucency of ceramic materials

STATEMENT OF PROBLEMnThe spectroradiometer (SR) was introduced as an alternative instrument to the spectrophotometer (SP) for measuring color in dentistry. No published studies were identified on the SR-based translucency of clinically simulated dental ceramics that closely reflect clinical conditions. Furthermore, it is unclear whether there is a correlation between SR- and SP-based translucency values.nnnPURPOSEnThe purpose of this study was to compare the translucency parameter (TP) of core, veneer, and layered ceramics determined by an SR, and to determine the correlations in TPs measured by an SR and a reflection SP.nnnMATERIAL AND METHODSnSeven A2 shade core ceramics and corresponding A2 and A3 shade veneer ceramics were fabricated with a layered thickness of 1.5 mm. The color of core, veneer, and A2- and A3-layered ceramics was measured over white and black backgrounds by an SR with 2 measuring apertures of 2.63 and 5.25 mm in diameter, and also by an SP (n=7). TP values were calculated and the differences in SR (5.25)-based TP values of the layered ceramics were analyzed with 2-way ANOVA with the fixed factors of shade designation and type of ceramic core (α=.05). The influence of the brand on the TP values of core, veneer, and A2- and A3-layered ceramics was also analyzed with 1-way ANOVA. Correlation analysis and paired t test were performed for the SR- and SP-based TP values (α=.05).nnnRESULTSnSR (5.25)-based TP values of layered ceramics ranged from 4.4 to 12.5, and were influenced by the type but not by the shade designation. SR-based TP values of core, veneer, and A2- and A3-layered ceramics were influenced by the brand. SR- and SP-based TP values were highly correlated (r=0.982 to 0.987, P<.01), although TP values based on SR measurement were significantly higher (P<.05).nnnCONCLUSIONSnSR measurements showed significantly different translucency for different types of clinically simulated ceramic specimens. TP values measured by the SR and the SP were significantly different but highly correlated.

Influence of TiO2 nanoparticles on the optical properties of resin composites

OBJECTIVESnTo determine the influence of titanium dioxide (TiO2) nanoparticle addition on the opalescence, color, translucency and fluorescence of experimental resin composites.nnnMETHODSnA light curing resin matrix was made by mixing 60 wt.% Bis-GMA and 40 wt.% TEGDMA. Silane coated glass filler (mean particle size: 1.55 microm) was added in the ratio of 50 wt.% of the resin composites. A fluorescent whitening agent was also added (0.05 wt.%). TiO2 nanoparticles (<40 nm) were added with the concentrations of 0, 0.1, 0.25 and 0.5 wt.%. Reflected and transmitted colors of 1 and 2 mm thick specimens were measured relative to the illuminant D65 with reflection spectrophotometers. Opalescence parameter (OP), color difference (DeltaE*ab), translucency parameter (TP), fluorescence parameter (FL), and fluorescence and opalescence spectra were calculated.nnnRESULTSnFor the 1 mm thick specimens measured with 3 mm x 8 mm rectangular aperture, when the concentration of TiO2 increased from 0% to 0.5%, OP increased from 2.4 to 18.0, TP decreased from 35.4 to 13.1, and fluorescence spectra remained unchanged. Color difference between these specimens was in the range of 3.4-6.6 DeltaE*ab units. OP values were significantly influenced by the thickness of the specimens and the configuration of the spectrophotometers (p<0.05).nnnSIGNIFICANCEnAddition of TiO2 nanoparticles significantly increased the opalescence of resin composites while leaving the fluorescence spectra unchanged; however, it significantly decreased the translucency and also changed the color (p<0.05). Resin composites with 0.1-0.25% TiO2 nanoparticle would simulate the opalescence of human enamel.

Differences in color, translucency and fluorescence between flowable and universal resin composites

OBJECTIVESnTo evaluate the optical properties such as color, translucency and fluorescence of flowable resin composites, and compare them with the corresponding shade universal resin composites of the same brand.nnnMETHODSnFour brands of flowable and universal resin composites of the same shade designation (A2) were investigated. Color of specimens (2mm in thickness) was measured after polymerization on a reflection spectrophotometer over background of white, black and each corresponding composite material itself. Color differences (DeltaE(ab)(*)) between each combination of resin composites were determined. Translucency parameter (TP) and color difference by the fluorescent emission (DeltaE(ab)(*)-FL) of materials were also calculated. Differences in the optical properties of flowable and universal resin composites were analyzed with one-way ANOVA.nnnRESULTSnDeltaE(ab)(*) between the flowable and the corresponding universal resin composites was in the range of 1.0-6.0 DeltaE(ab)(*) units, which was perceptible (DeltaE(ab)(*)>2.6) in three brands. Flowable resin composites revealed lower TP values in two of the four brands. DeltaE(ab)(*) between flowable and the corresponding universal resin composites was influenced by their difference in translucency. All the four universal resin composites and two flowable resin composites showed fluorescent peak, and the range of DeltaE(ab)(*)-FL was 0.3-2.3 DeltaE(ab)(*) units.nnnCONCLUSIONSnOptical properties of flowable and universal resin composites was significantly different (p<0.05); therefore, differences in color, translucency and fluorescence between the flowable and the corresponding universal resin composites should be considered for clinically acceptable color matching.

Influence of color parameters of resin composites on their translucency

OBJECTIVESnTo determine the influence of color parameters and the difference in color parameters by the background on the translucency of resin composites.nnnMETHODSnEight light-curing resin composites, a total of 41 shades, were investigated. The color of specimens was measured after polymerization on a reflection spectrophotometer with the SCE geometry over white and black backgrounds. The translucency parameter (TP), contrast ratio (CR) and the difference in color parameters by the background (DeltaL*, Deltaa*, Deltab* and DeltaC*ab: values over the white background minus value over the black background) were calculated. Correlations between TP values, CR values at every 50-nm interval and the color parameters as well as the differences in color parameters by the background were analyzed with regression analysis.nnnRESULTSnCorrelations between TP values, and the color parameters and the differences in color parameters were significant except chroma difference (p<0.01). The correlation between TP values and chroma was significant (r= -0.489 and -0.603, p<0.01). The correlation between TP values and DeltaL* was very high (r=0.868). Correlations between the color parameters, the differences in color parameters and CR values were varied by the wavelength. TP values were highly correlated with the CR value at the wavelength of 700 nm.nnnSIGNIFICANCEnMore chromatic shades of commercial resin composites were less translucent. Translucency increased as the wavelength increases.

Difference in the translucency of all-ceramics by the illuminant

OBJECTIVESnThe objective of this study was to determine the differences in the translucency parameter (TP) of all-ceramic core, veneer and layered specimens relative to the CIE standard illuminant D(65), A and F2.nnnMETHODSnThe A2-corresponding shade of seven all-ceramic core materials and one sintering ceramic as a reference were prepared in clinically relevant thicknesses (n = 7). The A2- and A3-corresponding shades of each recommended veneer ceramics were fabricated so that the thickness of the layered specimen was 1.5mm. The color of core, veneer and layered specimens was measured over white and black backgrounds relative to the illuminant D(65), A and F2 with a reflection spectrophotometer. TP value was obtained by calculating the color difference between the specimen over the white and that over the black background. Differences of TP values by the illuminant (DeltaTP) were analyzed with three-way analysis of variance (ANOVA), with the fixed factors of the type of ceramic, the brand/thickness of ceramic within each type and the combination of illuminants (alpha = 0.05).nnnRESULTSnDeltaTP values were influenced by three factors based on three-way ANOVA. Higher translucent materials showed higher difference in TP value by the illuminants. TP(D(65)) was lower than TP(F2) and TP(A) values. Correlation coefficients between TP values relative to the different illuminants were higher than 0.994 (p<0.01).nnnSIGNIFICANCEnTranslucency of all-ceramic materials under daylight condition was lower than those under incandescent or fluorescent lamps. Therefore, this difference should be considered when shade matching translucent shades of all-ceramics.

Lightness, chroma, and hue distributions of a shade guide as measured by a spectroradiometer

STATEMENT OF PROBLEMnThe 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.nnnPURPOSEnThe 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.nnnMATERIAL AND METHODSnLightness, 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).nnnRESULTSnThe 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.nnnCONCLUSIONSnThe 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.

Comparison of translucency between indirect and direct resin composites

OBJECTIVESnTo measure the translucency of indirect and direct resin composites after curing, and to determine the influence of material and shade group combination on these properties.nnnMETHODSnBelleGlass NG (BG, indirect resin composite) and Estelite Sigma (ES, direct resin composite), each composed in three shade groups (EN, OD and TL for BG; BS, AS and OP for ES) of 16 shades were investigated. Resin composite was packed into a mold (BEC) and was cured with a light-curing unit (CWL). Secondary curing was performed in a proprietary curing chamber (CIC) for BG material. Color was measured at the BEC, CWL and CIC conditions in the CIELAB scale using a spectrophotometer. Translucency parameter (TP) was calculated as the color difference between a specimen over a white and a black background.nnnRESULTSnTP values before curing were in the range of 7.7 (BG-OD) to 16.9 (ES-AS), and those after curing were in the range of 10.0 (BG-OD) to 21.5 (BG-EN). TP values of both materials were influenced by curing (p<0.05). There were significant difference in the TP values by the material and shade group combination, and the following homogenous subsets were found based on Tukey multiple comparison test: BG-OD<ES-OP<BG-TL=ES-AS=ES-BS<BG-EN (p<0.05).nnnCONCLUSIONSnBG material showed a wider range of TP values than ES, which would improve shade-matching capability of this material. Translucency should be considered when neighboring teeth are treated with different types of resin composites.

Shade compatibility of esthetic restorative materials—A review

OBJECTIVESnThe 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.nnnMETHODSnPublished 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.nnnRESULTSnSeveral 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.nnnSIGNIFICANCEnVisual 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.

Aesthetic colour performance of plastic and ceramic brackets — an in vitro study

Objective To evaluate the aesthetic colour performance (colour blending) of plastic and ceramic brackets by determining the colour changes of shade guide tabs before and after bracket placement. Design In vitro, laboratory study. Materials and methods Four plastic and four ceramic brackets were investigated (nu200a=u200a5). Brackets were placed on the labial surface of the A1 and A4 tabs of a Vitapan classic shade guide. The colours of the areas corresponding to the central and inferior areas of the brackets were measured before and after bracket placement according to the CIELAB colour scale with a spectroradiometer. Changes in colour (ΔE*ab) and colour coordinates (ΔL*, Δa*, Δb* and ΔC*ab) of the tabs after bracket placement were calculated. Results Colour changes in the central and inferior areas were in the ranges of 5·6–11·1 and 4·3–12·3 ΔE*ab units, respectively. Changes in colour and colour coordinates were influenced by shade tab colour and bracket brand (P<0·05). Compared to A1 tab, ΔE*ab, Δa*, Δb* and ΔC*ab values on A4 tab were significantly higher (P<0·01). The hybrid polymer bracket and glass reinforced plastic bracket induced the smallest colour changes in the central and inferior areas. Conclusions All the investigated aesthetic brackets induced clinically unacceptable (ΔE*ab>5·5) or perceptible (ΔE*ab>2·6) colour changes when placed on the shade tabs. Aesthetic colour performance of brackets on the less chromatic and lighter tab was better than that on the more chromatic and dark tab. High translucency of bracket alone did not lead to better aesthetic colour performance.