Color Correlations among Six Types of Permanent Anterior Teeth.

STATEMENT OF PROBLEM: When multiple teeth are missing, the color for missing teeth should be estimated based on the color of remaining teeth. PURPOSE: The purpose was to determine the strength of color correlations among six types of permanent anterior teeth. METHODS: Color of 12 anterior teeth was measured by Shade Vision System for 47 volunteers. The color coordinates in each type of teeth such as maxillary central incisor (MX1), lateral incisor (MX2), and canine (MX3), and mandibular central incisor (MD1), lateral incisor (MD2), and canine (MD3) were determined. Correlations and differences among the corresponding color coordinates of each type of teeth were determined. RESULTS: Compared with MX1, the differences were in the range of -3.2 to -6.5 in L*, 0.5 to 2.7 in a*, -0.7 to 7.5 in b*, and the color difference (ΔE*ab ) was 4.5 to 10.3. The color difference by ΔE00 formula was 3.1-6.7. Although the color coordinates were different by tooth type, they generally showed correlations (p < 0.001). CONCLUSIONS: For the color estimation of missing MX1, the color coordinates of MD1 were the strongest predictors. In case of missing MX3, L* and a* of MD3 and b* of MX1 were the strongest predictors for each corresponding coordinates. CLINICAL SIGNIFICANCE: The color for missing teeth, especially for maxillary central incisor and maxillary and mandibular canines, could be estimated based on those of the same type teeth on the opposing arch. These results should be applied for clinical color selection for missing teeth.(J Esthet Restor Dent 28:S5-S13, 2016).

Engineered microstructure granules for tailored drug release rate.

Biomaterials developed for controlled drug delivery have demonstrated excellent results in the present study. A biomaterial prepared using hydroxyapatite (HAp) was shown to have a hollow structure with the presence of interconnected pores to house drug carriers. The poly(lactic-co-glycolic acid) particles were used as drug carriers loaded with dexamethasone, a corticosteroid that is known to promote osteoinduction. The surface of the drug carriers was modified using polyethyleneimine, and then conjugated to the surface of HAp granules. The hollow HAp granules had drug carriers on both their inner and outer surfaces and showed a controlled drug release rate that was comparable to that of granules containing drug carriers on their outer surface alone. The pores were designed for insertion of drug carriers and preosteoblasts. Consequently, the biomaterials influenced cellular behavior by first promoting cell proliferation and then inducing early stage osteogenic differentiation. The effects of controlled release rate were evidenced for up to two weeks after cell seeding, resulting in an increase of osteogenic differentiation. In summary, drug carriers loaded onto hollow HAp granules were shown to be suitable for patients who require replacement of missing bone for repair of bone fractures that are extremely complex, pose a significant health risk to the patient, or fail to heal properly.

Color assimilation of resin composites with adjacent color according to the distance.

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) mm(3) 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.

Cytotoxicity test of dentin bonding agents using millipore filters as dentin substitutes in a dentin barrier test.

OBJECTIVES: The purpose of this study was to find proper dentin substitute for standardized dentin barrier test and perform the cytotoxicity test of commercial bonding agents with the proper substitute. MATERIALS AND METHODS: The three-dimensional cells attached to dentin disc or millipore filters as the dentin substitute were tested in a dentin barrier test by perfusion. MTT assay was performed as an evaluation method for the cell survival rate. The cytotoxicity test of serial phenol dilution by bovine dentin disc was done to determine a standard toxic material, and the test of this proper phenol by using various millipore combinations was performed to find the suitable dentin substitute. Also, the cytotoxicity test of bonding agents was performed by this standardized substitute. The cell viability was expressed as percentages of untreated group. RESULTS: Phenol concentration of 0.05 % was selected as the standard toxic material. The different combinations of millipore filters--two sheets of 0.45 µm, two sheets of 0.22 µm, and the combination of 0.65, 0.45, and 0.22 µm--showed similar cytotoxicity to natural dentin discs by 0.05 % phenol (p > 0.05). The millipore combination of 0.65, 0.45, and 0.22 µm that had structural similarity to natural dentin discs was used as the substitute for cytotoxicity test of bonding agents. The toxic level of Adper Prompt L-Pop using the selected substitute was significantly the highest among four kinds of dentin bonding agents (p < 0.05). Also, the dentin barrier test by the substitute showed constant results compared with the one by the natural dentin disc. CONCLUSIONS: The millipore filter combination of 0.65, 0.45, and 0.22 µm could be used as the substitute for the cytotoxicity test of materials applied to dentin. CLINICAL RELEVANCE: Dentin barrier test by standardized substitutes would be helpful for considering the potential toxicity of dentin bonding agents prior to clinical adaptations and reducing the variations of natural bovine dentin that has individually different characteristics.

Resolution of surgically created three-wall intrabony defects in implants using three different biomaterials: an in vivo study.

OBJECTIVES: To histomorphometrically analyze bone formation on amorphous calcium phosphate (ACP), micro-macroporous biphasic calcium phosphate (MBCP), and freeze-dried bone allograft (FDBA) in three-wall defects adjacent to structured surface with calcium phosphate nanocoating implants in dogs. MATERIALS AND METHODS: Five male mixed-breed dogs were used in this study. The premolars and molars were extracted on both sides of the mandible. Eight weeks after extraction, four implants were submerged on each side of the mandible. Three-wall intrabony defects (5 × 3 × 3 mm) were surgically created adjacent to the implants before installation. No grafts were placed in the control group. At the experimental sites, each intrabony defect was grafted with either ACP, MBCP, or FDBA. The dogs were sacrificed after 12 weeks, and histological and histomorphometrical analyses of the implant sites were performed. RESULTS: All of the three experimental groups exhibited defect resolution and osseointegration that showed a statistically significant difference compared with the control group in terms of remaining defect depth and bone-to-implant contact (BIC). However, there were no statistical significances among the three experimental groups. MBCP had the highest BIC (63.57 ± 21.57%), followed by ACP and FDBA. The control group showed the least bone area and the greatest remaining defect depth. CONCLUSION: Grafts with the synthetic biomaterials ACP and MBCP showed bone regeneration that was similar to FDBA in surgically created three-wall intrabony defects adjacent to implants. Within the limitations of this study, it can be concluded that ACP and MBCP synthetic biomaterials are as effective as FDBA at osteoconduction.

Drug-loaded porous spherical hydroxyapatite granules for bone regeneration.

Porous spherical hydroxyapatite (HAp) granules, which are not only can be used for bone void filler, but also drug delivery systems, were prepared using a liquid nitrogen method. Various pore and channel structures of spherical granules were obtained by adjusting the ratio of water to HAp powder and the amount of sodium chloride (NaCl). By using the water to powder ratio at 2.0 ml/g and the amount of NaCl at 15 wt% by powder, the spherical granules have optimal pore volume, micro-channel structure and strength to handle as well as the ability to work as a drug delivery system. When the NaCl content was 15 wt%, the micro-channel structure was changed, but the pore volume was maintained. For the drug release test, dexamathasone (Dex) was loaded as a model drug on the prepared HAp granules by the immersion method, and the drug release behavior was curved by a UV/vis spectrophotometer. As a result, different drug release behavior was observed according to micro-channel structural differences. Therefore, it was concluded that the NACl could be applied as the pore and micro-channel structure control agent. Porous spherical HAp granules, which were fabricated by a liquid nitrogen method, show potential as bone void filler with the ability of controlled drug release.

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.

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 (n=5). 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.

Physical properties of resin-reinforced glass ionomer cement modified with micro and nano-hydroxyapatite.

Hydroxyapatite is a biologically compatible material and a major component of dental enamel and bone tissue. Because of its biocompatibility and structural similarity to human teeth and the skeletal system, a number of dental studies have evaluated its application as a bone substitute or dental restorative material. This study was to evaluate the differences in bonding strength and resistance to demineralization between micro-hydroxyapatite and nano-hydroxyapatite added to self-cured resin-reinforced/modified glass ionomer cement. RelyX was used as the base glass ionomer cement material and for the control group. 10% micro-hydroxyapatite added glass ionomer cement was named experimental group 1, and 10% nano-hydroxyapatite added glass ionomer cement was named experimental group 2. Physical tests for ISO9917-1:2007 in each group was acceptable, except the setting time of nano-hydroxyapatite added glass ionomer cement, which exceeded maximum setting time. Bonding strength was greatest in nano-hydroxyapatite glass ionomer cement, and cohesive failure was common in all specimens. When fractured surface was observed under SEM, spherical particles were observed in experimental groups containing hydroxyapatite particles, and they were more prevalent in nano-HA added glass ionomer cement group than in micro-hydroxyapatite added group. Both experimental groups exhibited greater resistance to demineralization compared to the control group, and there was no significant difference between the experimental groups. Under SEM, nano-hydroxyapatite added glass ionomer cement exhibited increased resistance to demineralization compared to micro-hydroxyapatite added glass ionomer cement.

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.

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

STATEMENT OF PROBLEM: 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. PURPOSE: 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. MATERIAL AND METHODS: 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). RESULTS: 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. CONCLUSIONS: 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.

Effects of aging and HEMA content on the translucency, fluorescence, and opalescence properties of experimental HEMA-added glass ionomers.

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.

Comparison of the color stability of flowable and universal resin composites.

PURPOSE: To evaluate the color stability of flowable resin composites after ultraviolet (UV) irradiation and thermocycling, and to compare the color stability with the corresponding shade universal resin composites of the same brand. METHODS: Five specimens each (10 mm in diameter and 2 mm in thickness) of four brands of flowable and universal resin composites (shade A2) were light-cured. Baseline color was measured on a reflection spectrophotometer over a white background. Artificial aging was performed with a filtered xenon lamp (irradiation intensity: 550 W/m2) for 24 hours and then color was measured. Afterwards, thermocycling was performed for 3,000 times between 5 and 55 degrees C and color was measured again. Changes in color (deltaE*ab) and color parameters (deltaL*, deltaa*, deltab* and deltaC*ab) during the UV irradiation, the thermocycling and both aging protocols were calculated. Differences in the color change of the flowable and the universal resin composites were analyzed with two-way repeated measures ANOVA by the combination of brand and type (eight groups) of materials and aging protocol (P < 0.05). RESULTS: Color changes during the UV irradiation, the thermocycling and both aging protocols were in the range of 2.3-6.8, 0.6-0.8 and 2.6-6.2 deltaE*ab units, respectively. Flowable resin composites showed higher color change during the UV irradiation and was significant in three of the four brands (P < 0.05). The same results were obtained after both aging protocols. Changes in color parameters were varied by the brand and type of resin composites (P < 0.05).

Color difference of all-ceramic materials by the change of illuminants.

PURPOSE: To determine the differences in color and color parameters (lightness, chroma and hue) of simulated layered all-ceramic specimens at a clinically relevant thickness under three CIE standard illuminants. METHODS: Seven all-ceramic core materials of A2-corresponding shade, one sintering ceramic and one alloy core as references were prepared in clinically relevant thicknesses (0.4 to 0.8 mm). A2- and A3-corresponding shades of each of the recommended veneer ceramics were fabricated so that the thickness of the layered specimens was 1.5 mm. Bovine dentin was also used as a reference. Color was measured relative to the CIE standard illuminants D65, A and F2 with a reflection spectrophotometer. Differences in color and color parameters by the change of illuminants were calculated. Repeated measures two-way ANOVA with the fixed factor of the brand of ceramics on the difference in color and color parameters by the change of illuminants (D65 to A, D65 to F2 and A to F2) was performed (alpha = 0.05). RESULTS: Color difference (deltaE*ab) was in the range of 0.6 to 0.8 for bovine dentin, 1.3 to 3.4 for A2-veneer layered specimens and 1.6 to 4.2 for A3-veneer layered specimens. Differences in color and parameters were significantly influenced by the brand of the ceramics and the combination of illuminants (P < 0.05).

Difference in illuminant-dependent color changes of shade guide tabs by the shade designation relative to three illuminants.

PURPOSE: To determine the difference in illuminant-dependent color changes of shade guide tabs of Vita Lumin (VITA), Chromascop (CHRO) and Vita 3D-Master (3D-M) shade guides by the shade designation in each shade guide. METHODS: Color of 16 tabs of VITA, 20 tabs of CHRO and 29 tabs of 3D-M was measured according to the CIELAB color scale relative to the CIE standard illuminant D65, A and F2. Color differences (deltaE*ab) between the A1 tab and other VITA tabs, between the 110 tab and other CHRO tabs and between the 0M1 tab and other 3D-M tabs relative to the three illuminants were calculated, and the ratios of deltaE*ab values relative to the different illuminants [deltaE*ab(A)/deltaE*ab(D65), deltaE*ab(F2)/deltaE*ab(D65) and deltaE*ab(F2)/deltaE*ab(A)] were calculated. Ratios of the hue angle shifts of each shade tab by the change of illuminant over the corresponding value of the Al, the 110 or the 0M1 tab were also calculated. Differences in the ratios of color difference and hue angle shift were analyzed with a repeated measures, two-way analysis of variance (alpha = 0.05). RESULTS: Ratios of deltaE*ab values by the illuminant were 0.90-1.17, 0.95-1.07 and 0.99-1.06 for the VITA, the CHRO and the 3D-M shade guide, respectively. Ratios of the hue angle shifts by the illuminant were from -1.6 to 1.8 for the VITA, from -7.3 to 1.2 for the CHRO and from -1.2 to 3.1 for the 3D-M. Changes in color and hue angle of shade tabs were significantly different by the shade tab designation when illuminant was changed (P < 0.01).

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.

Measurement of discolouration of orthodontic elastomeric modules with a digital camera.

The objective of this study was to measure discolouration using a digital camera on various types of clear orthodontic elastic modules, immersion solutions, and time periods to determine whether the cause of discolouration of these modules was due to simple staining, chemical degradation, or both. Three types of clear orthodontic elastomeric modules were investigated [Plastic ligatures (AO); Power 'O's 012 (OC); dispense-A-tie (TP)]. The elastomeric modules were immersed in the stretched condition in distilled water (control group) and in 75 per cent ethanol for chemical degradation and 2 per cent methylene blue for simple staining. After 0, 1, 2, 3, 6, 9, 12, 15, 18, and 21 hours and 1, 2, 3, 4, and 5 days of immersion, digital images of the modules were taken and processed using commercial software. The differences in colour changes depending on the type of elastomeric modules, immersion solution, and immersion period were analysed using a three-way analysis of variance and Tukey's multiple comparison test. The colour changes in the ethanol and methylene blue solutions by immersion period were analysed with regression analysis. There were significant differences in discolouration depending on the type of elastomeric modules, immersion solution, and immersion period (P < 0.05). The range of colour changes (Delta E* ab) was 1.0-20.0 units for AO, 0.6-30.0 units for OC, and 1.1-18.8 units for TP, independent of immersion solution and time. Methylene blue resulted in the greatest colour change. Discolouration due to chemical degradation by the ethanol solution mainly occurred in the first few hours, reached a plateau with no further increase over time, and was greater than staining by methylene blue in that period. Discolouration due to staining by methylene blue, however, continued to increase over the whole immersion period. Therefore, discolouration of elastomeric modules was a result of chemical degradation as well as staining in the early stages but in the later stages was due only to simple staining.

Correlations between color differences based on three color-difference formulas using dental shade guide tabs.

PURPOSE: The purpose of this study was to determine the correlation among color-difference values based on three formulas between shade tab pairs from two shade guides [Vita Lumin (VITA) and Chromascop (CHRO)]. MATERIALS AND METHODS: The color of shade tabs was measured relative to the standard illuminant D(65) under the 8 degrees standard observer function, and distributions for CIE L*, a*, and b* values were compared. One hundred and twenty shade pairs from VITA and 190 shade pairs from CHRO were used to calculate color differences using CIELAB, DIN99, and CIEDE2000 formulas (DeltaE*(ab), DeltaE(99), and DeltaE(00), respectively). A paired t-test was used to determine the difference between each pair of the three color-difference values (alpha= 0.01). Regression analysis was used to determine the correlations between the color differences (alpha= 0.01). RESULTS: For both shade guides, there were significant differences between DeltaE*(ab) and DeltaE(00), DeltaE*(ab) and DeltaE(99), and DeltaE(99) and DeltaE(00) (p < 0.01). DeltaE*(ab) and DeltaE(00), and DeltaE*(ab) and DeltaE(99) were strongly correlated (r(2)= 0.90 to 0.94, p < 0.05). Although a simplified a* rescaling function of the CIE a* axis has been added in the CIEDE2000 formula, the influence of the opposite signs in the a* value were found to be irrelevant to the DeltaE(00) value. CONCLUSION: DeltaE*(ab),DeltaE(99), and DeltaE(00) can be used interchangeably for the evaluation of color difference of shade tabs.

Fabrication of collagen hybridized elastic PLCL for tissue engineering.

Biodegradable elastic poly(L-lactide-co-epsilon-caprolactone) (PLCL) (50:50) copolymer was blended with collagen (0.05, 0.1 and 0.2% w/w) in an acidic dioxane solution to form a collagen/PLCL hybrid material suitable for tissue engineering applications. Stability and dispersivity of collagen on collagen/PLCL hybrid films and collagen coated PLCL films under mechanical stress were determined by a collagen release test and water contact angle measurement. Hybrid films had a higher stability than collagen-coated PLCL films. Elastic recovery as well as high interconnectivity and uniform pore morphology of the hybrid scaffolds were not affected by the collagen concentration. Fibroblasts (NIH-3T3) cell culture test was performed for cell growth and viability evaluation. Collagen concentration had little affect on the initial cell adhesion after 4 h cell culture; but after 48 h cell culture, increased cell proliferation on the hybrid films was observed. The hybrid material can be applied as a scaffold for vessel and cartilage regeneration for mechano-active tissue engineering.

Influence of filler on the difference between the transmitted and reflected colors of experimental resin composites.

OBJECTIVES: This study sought to determine the influence of filler size and amount on the difference between the transmitted and reflected colors and the translucency of experimental resin composites. METHODS: The color of experimental resin composites (38 mm in diameter and 1 mm in thickness) was measured in the transmittance and reflectance modes. Opalescence parameter (OP) was calculated as the difference in blue-yellow and red-green coordinates between the transmitted and reflected colors. Translucency parameter (TP) was calculated as the color difference between the reflected colors over a white and a black background. RESULTS: The range of OP was between 1.0 and 5.7, which was varied by the size and amount of filler. TP decreased as the amount of filler increased when the filler size was the same. SIGNIFICANCE: Controls on the proper filler size and amount should be studied further to modify the opalescence and translucency of resin composites, considering also the effect of filler on mechanical properties.