Ho-Nam Lim

Spectroradiometric and spectrophotometric translucency of ceramic materials

STATEMENT OF PROBLEM The 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. PURPOSE The 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. MATERIAL AND METHODS Seven 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). RESULTS SR (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). CONCLUSIONS SR 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.

Perceived color shift of a shade guide according to the change of illuminant

STATEMENT OF PROBLEM The perceived color of shade guide tabs is influenced by different spectral compositions of different light sources, and this can influence color matching. PURPOSE The purpose of this study was to determine the amount of perceived shift in color and color coordinates of a shade guide using 3 different light sources: CIE standard illuminant D65 (daylight), A (incandescent lamp), and F9 (fluorescent lamp). MATERIAL AND METHODS CIE color coordinates L*, a*, b*, chroma, and the spectral reflectance of shade tabs in a shade guide (Vitapan 3D-Master) were measured by a spectroradiometer under D65, A, and F9 simulators. Perceived color and color coordinate shifts due to the change of illuminant were determined. The influence of the type of light and shade designation of the 26 tabs on the color coordinates was analyzed by a 2-way ANOVA; correlations in the color coordinates between each corresponding pair under the 3 illuminants were determined (α=.05). RESULTS All of the color coordinates were influenced by the type of illuminant and shade designation of the shade tabs (P<.001); however, each corresponding coordinate pair showed significant correlations under different illuminants (r=0.930 to 0.997, P<.01). Color differences under different illuminants were in the range of 3.1 to 9.1 ΔE units; all of these differences were perceptible (ΔE>2.6). Lightness decreased and chroma increased when the illuminant was changed from the D65 simulator to the A or F9 simulators. CONCLUSIONS Perceptible shifts in the color of shade guide tabs under different ambient lighting conditions were confirmed by a spectroradiometer; these color shifts were influenced by the type of illuminant used.

Shade compatibility of esthetic restorative materials—A review

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.

Difference in the color stability of direct and indirect resin composites

Indirect resin composites are generally regarded to have better color stability than direct resin composites since they possess higher conversion degree Objective The present study aimed at comparing the changes in color (∆E) and color coordinates (∆L, ∆a and ∆b) of one direct (Estelite Sigma: 16 shades) and 2 indirect resin composites (BelleGlass NG: 16 shades; Sinfony: 26 shades) after thermocycling. Material and Methods Resins were packed into a mold and light cured; post-curing was performed on indirect resins. Changes in color and color coordinates of 1-mm-thick specimens were determined after 5,000 cycles of thermocycling on a spectrophotometer. Results ∆E values were in the range of 0.3 to 1.2 units for direct resins, and 0.3 to 1.5 units for indirect resins, which were clinically acceptable (∆E<3.3). Based on t-test, ∆E values were not significantly different by the type of resins (p>0.05), while ∆L, ∆a and ∆b values were significantly different by the type of resins (p<0.05). For indirect resins, ∆E values were influenced by the brand, shade group and shade designation based on three-way ANOVA (p<0.05). Conclusion Direct and indirect resin composites showed similar color stability after 5,000 cycles of thermocycling; however, their changes in the color coordinates were different.

Correlations between spectroradiometric and spectrophotometric colors of all-ceramic materials.

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 (1.5mm after layering). Color of layered specimens was measured according to the CIELAB color scale by a SP and a SR. Color differences (ΔE(ab)(*)) 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.

Effects of aging procedures on the molecular, biochemical, morphological, and mechanical properties of vacuum-formed retainers

The influence of intraoral exposure procedures on the physical characteristics of thermoplastic vacuum-formed retainers (VFRs) is still unclear. The effects of thermoforming and intraoral use on the molecular, chemical, morphological, and mechanical properties of thermoplastic VFRs were investigated. VFRs with a 0.8-mm-thick thermoplastic PETG sheet acquired from 48 patients were investigated with two aging procedures, including vacuum forming and intraoral exposure, for 2-week and 6-month. Eight evaluating sites for thermoplastic VFRs were assessed with seven analytical techniques. LM, SEM, and AFM microscopic findings showed that the surface characteristics increased with increasing in vivo exposure time (a four-fold increase) and varied depending on the sites evaluated (an occlusal surface). Raman and EDX spectroscopic findings showed that aging procedures led to a significant change in the molecular composition of VFRs, leading to a decrease in the composition rate of carbon (C) and the presence of silicon (Si), phosphorus (P), and calcium (Ca). Compressive strength and tensile tests showed that aging procedures led to a significant increase (P<0.01) in ultimate tensile strength, elastic modulus, the stored energy at a 6-mm deflection (u6 mm), and the compressed load at a 3-mm deflection (σ3 mm). Thermoforming led to a smoother surface and no crystallization of PETG sheets. Intraoral exposure accelerated changes in surface morphology, tensile strength, and elastic modulus of VFRs. This change was site-specific and enhanced with an increase in intraoral exposure time. Therefore, thermoforming and in vivo oral exposure procedures led to the molecular, morphological, and mechanical properties of thermoplastic VFRs.

Variation in instrument-based color coordinates of esthetic restorative materials by measurement method—A review

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.

Graphene quantum dot-based theranostic agents for active targeting of breast cancer

A novel graphene quantum dot (GQD)-based nanocarrier labeled with Herceptin (HER) and β-cyclodextrin (β-CD) was developed as a promising theranostic candidate for the treatment of breast cancer. Each component of this nanocarrier plays a critical role in providing multiple functions to achieve enhanced anticancer activities. HER provides active targeting to HER2-overexpressed breast cancer to enhance accumulation in the cancer cells. β-CD provides a site for loading of a hydrophobic anticancer drug, doxorubicin (DOX), via “host–guest” chemistry. The nanocarriers also provide diagnostic effects due to the blue-color emission of the GQDs. In response to the acidic environment of cancer cells, the GQD-complex degraded rapidly and the DOX was released in a controlled manner to inhibit proliferation of cancer cells. This multi-functional drug delivery system leads to a synergistically enhanced anticancer strategy which provides treatment and diagnosis. The intracellular trafficking results, along with cell viability and confocal laser scanning microscopy, suggest that the GQD-complex offers a viable strategy for HER2-overexpressed breast cancer-targeting drug delivery applications.

Influence of HEMA content on the mechanical and bonding properties of experimental HEMA-added glass ionomer cements

The purpose of this study was to determine the influence of incrementally added uncured HEMA in experimental HEMA-added glass ionomer cement (HAGICs) on the mechanical and shear bond strength (SBS) of these materials. Increasing contents of uncured HEMA (10-50 wt.%) were added to a commercial glass ionomer cement liquid (Fuji II, GC, Japan), and the compressive and diametral tensile strengths of the resulting HAGICs were measured. The SBS to non-precious alloy, precious alloy, enamel and dentin was also determined after these surfaces were subjected to either airborne-particle abrasion (Aa) or SiC abrasive paper grinding (Sp). Both strength properties of the HAGICs first increased and then decreased as the HEMA content increased, with a maximum value obtained when the HEMA content was 20% for the compressive strength and 40% for the tensile strength. The SBS was influenced by the HEMA content, the surface treatment, and the type of bonding surface (p<0.05). These results suggest that addition of an appropriate amount of HEMA to glass ionomer cement would increase diametral tensile strength as well as bond strength to alloys and teeth. These results also confirm that the optimal HEMA content ranged from 20 to 40% within the limitations of this experimental condition.

Vitapan 3D-master shade guide showed no fluorescence emission

OBJECTIVES To determine the fluorescence property of Vitapan 3D-Master shade guide tabs with a spectrophotometer. MATERIALS AND METHODS Fluorescence property of 29 shade tabs, in both of original and ground-to-flat forms, was determined by a reflection spectrophotometer. Color difference (ΔE*ab-FL) by the inclusion and exclusion of the UV component of a standard daylight simulator (CIE standard illuminant D65) was calculated to determine the fluorescence color change. Fluorescence peak was expressed as the difference in spectral reflectance values by the UV component. RESULTS AND CONCLUSION ΔE*ab-FL values were in the range of 0.2 to 2.7 (mean: 1.2 ± 0.6) for the original and 0.5 to 1.6 (mean: 0.9 ± 0.1) for the ground-to-flat tabs, which was significantly different based on paired t-test (p<0.05); however, fluorescence peak was not detected in all the shade tabs. Therefore, fluorescence property of Vitapan 3D-Master shade guide should be modified to have similar fluorescence property of natural teeth and corresponding restorative materials.