Acceptable Color Difference Research Articles

Bleaching versus color change resistant adhesive in the discoloration of bracket-bonded tooth surfaces: an in vitro study

ObjectivesThe aim of this study was to compare the effect of office bleaching of teeth bonded with Transbond XTTM (3M Unitek, Monrovia, CA, USA) (TRXT) and the use of color change resistant Orthocem (FGM, Joinville, Brazil) in bracket bonding on coffee-induced enamel discoloration.Materials and methodsEighty premolars were distributed in equal numbers (n = 20) to group 1 (TRXT + distilled water), group 2 (TRXT + coffee solution), group 3 (TRXT + coffee solution + bleaching), and group 4 (Orthocem + coffee solution). Color was measured using a SpectroShade Micro (MHT, International, Verona, Italy) device at the beginning (T0), after coloring (T1), after bleaching (T1B), and after debonding (T2). ΔE color change values were calculated as T1-T0, T1B-T0 and T2-T0 differences. The conformity of the data to the normal distribution was examined with the Shapiro–Wilk test. Multiple comparisons were made with Tamhane’s T2 test and Tukey’s HSD test using one-way analysis of variance in the comparison of normally distributed data, and multiple comparisons were made with Dunn’s test using the Kruskal–Wallis H test for comparison of non-normally distributed data. The significance level was set at p < 0.050.ResultsA statistically significant (p < 0.001) difference was found between the T1-T0 and T2-T0 stages for group 1–4 ΔE values. A statistically significant (p < 0.001) difference was also found when the T1B-T0 ΔE values of group 3 were compared with the T1-T0 ΔE values of groups 1, 2, and 4.ConclusionsAfter coffee-induced enamel discoloration, bleaching of teeth bonded with TRXT produced acceptable color difference of the incisal, middle, and gingival regions of the crown. In teeth bonded with Orthocem, acceptable color difference was seen only in the middle of the crown.Clinical relevanceThe presented study will guide the clinician on how enamel discoloration side effect of fixed orthodontic appliance can reduce.

Analyzing the Effects of Plasma Treatment Process Parameters on Fading of Cotton Fabrics Dyed with Two-Color Mix Dyes Using Bayesian Regulated Neural Networks (BRNNs)

ABSTRACT This study used Bayesian Regulated Neural Networks (BRNN) with 10-fold cross-validation to accurately forecast fading effects of plasma treatment on cotton fabrics for a given set of parameters. By training six independent BRNN models, a reduction in model complexity and an enhancement in generalizability to unknown datasets were achieved. The input comprises plasma treatment parameters and color measurements of the cotton fabric before fading, while the output comprises color measurements after fading. The plasma treatment parameters included color depth, air (oxygen) concentration, water content and treatment time. Color measurements included CIE L*a*b*C*h and K/S values. Furthermore, 162 datasets derived from two-color mixed-dye cotton fabrics were utilized for training and testing. The outcomes revealed superior prediction performance of the BRNN compared to the Levenberg-Marquardt Neural Networks, with R2 values approaching 1 and 82.35% to 94.12% of the sample predictions lying within the acceptable color difference range. Through global sensitivity analysis, the impact of treatment parameters on fading effects was quantified, providing a scientific basis for parameter adjustment. This study not only elucidated the mechanism of plasma treatment-induced fading but also offers effective prediction tools for the intelligent and digital development of the fashion clothing fading domain.

In vivo Evaluation of Shade Replication of Different Generations of Zirconia to Natural Teeth Using Digital Color Determinations.

The color difference between the final shade of restorations milled from different zirconia blocks, and the control teeth in the esthetic zone is yet uncertain. For eight patients who required a singular maxillary central incisor restoration, twenty-four crowns made of zirconia were created. These were grouped into three categories based on the shade and nature of zirconia (Zr) utilized (white core, colored core, and monolithic high-translucency (ht) Zr crowns). The difference in color (ΔE) between the three zirconia crowns and the neighboring teeth was calculated by the use of Easyshade spectrophotometer. Two shades of resin luting cement were used. The measured ΔE values were evaluated based on a clinically acceptable color difference of 1.6ΔE, which is not visible to the human eye. Among the three groups, no differences of statistical significance were observed in terms of ΔE with different Zr types and resin cement color. Within the limits of this study, the usage of different shades of zirconia blanks and resin cements did not display a statistically significant effect on the final color of the crown. Changing the shade of resin cements does not appear to add value to the final shade of crown. In addition, the generation of zirconia does not influence the shade of the crown. Crowns made of zirconia can be cemented with opaque or transparent cement with no effect on the final color.

Performance of two-flux and four-flux models for predicting the spectral reflectance and transmittance factors of flowable dental resin composites.

To evaluate the prediction accuracy of the Kubelka-Munk Reflectance Theory and other more innovative two-flux and four-flux models for predicting the reflectance and transmittance factors of two flowable dental resin composites of various thicknesses within clinically acceptable color difference. Cylindrical samples of Aura Easy Flow resin composite (Ae1, Ae2, Ae3, Ae4 shades) and Estelite Universal Flow SuperLow resin composite (A1, A2, A3, A3.5, A4, A5 shades) were prepared with thicknesses ranging from 0.3mm to 1.8mm. Their reflectance and transmittance factors were measured with a spectrophotometer based on an integrating sphere, and were also predicted by 3 different two-flux models and 2 different four-flux models. The accuracy of reflectance and transmittance factor predictions was assessed using the CIEDE2000 color distance metric and 50:50% acceptability and perceptibility threshold criteria. Eymard's four-flux model is found to be the most accurate for predicting the spectral reflectance and transmittance factors, with 85% (resp. 100%) of all color deviations below the acceptability threshold, and below the perceptibility threshold for 40% (resp. 57%) of the samples with thickness ranging from 0.3 to 1.8mm in reflectance (resp. transmittance) mode. The Kubelka-Munk Reflectance Theory is found to be the least accurate model for predicting the spectral reflectance and transmittance factors of dental resin of thickness ranging from 0.3 to 1.8mm. Eymard's four-flux model enables to predict the color of slices of dental materials within acceptable color differences. Eymard's four-flux model's optical parameters thus describe light-matter interactions in dental materials more accurately than state of the art Kubelka-Munk Reflectance Theory.

Application of Image Color Gamut Boundary Judgment Algorithm in Digital Media

Image chromatic aberration evaluation is one of the research hotspots and academic difficulties in the field of color science and imaging technology. Based on the algorithm theory of image color gamut boundary judgment, this paper constructs its application model in digital media. The model uses the threshold color difference image as a reference and applies it to the evaluation experiment of color difference above the threshold based on the quantitative estimation method. During the simulation process, the improved HAD dual-color image digital boundary judgment algorithm is programmed. For small color difference data at the threshold level, the calculated color difference of the boundary judgment algorithm framework is smaller than the visual perception color difference; for the large color difference data above the threshold, the boundary judgment algorithm framework is given. The research results of the threshold color difference experiment show that the perceptible color difference threshold and acceptable color difference threshold of image color gamut observers for image color difference are 1.85 AE and 3.63 AE, respectively, which are basically twice the relationship. The visually perceptible chromatic aberration threshold and acceptable chromatic aberration threshold for lightness parameters are higher than those of chroma and hue, which shows that the boundary judgment algorithm framework has certain advantages for the evaluation performance of color digital image threshold chromatic aberration and effectively improves the algorithm robustness.

Influence of manufacturing technique on the color of zirconia restorations: Monolithic versus layered crowns.

The study aimed to compare the color of monolithic and layered zirconia crowns fabricated using different brands in the cervical, middle, and incisal areas. A total of 45 crowns were fabricated from three brands (Katana, Nacera, Cercon) using three methods (monolithic=ML (n=5), cut-back + enamel=BL (n=5), cut-back + dentin + enamel=TL (n=5)). CIE L*, a* b*, C*, h° color coordinates were recorded with a dental spectrophotometer in cervical, middle, and incisal areas. Color differences between manufacturing techniques, tooth areas, and brands were calculated using the CIEDE2000(1:1:1) formula, and the values were compared to the perceptibility (PT00 ) and acceptability thresholds (AT00 ). Comparisons between color coordinates were analyzed statistically (Kruskal-Wallis and Mann-Whitney U tests, p < 0.001). Significant differences were found between CIE L*, a*, b*, C*, h° coordinates of the zirconia crowns (p <0.001), generally. The lowest color differences were obtained between BL and TL crowns in cervical and middle areas. Color differences between cervical and middle areas were mostly below PT00 . An acceptable color difference was found between Katana and Cercon crowns. The manufacturing technique and the brand influenced the color of zirconia crowns. Also, the color of the crowns varied from cervical to incisal. Reproducing the optical properties of teeth with ceramic crowns might be challenging, given the differences in the internal configuration of the enamel and dentine, as well as their complex behavior when interacting with light. When deciding whether to fabricate a monolithic crown in translucent zirconia or improve its appearance by layering with more translucent glass-ceramic, the clinicians and dental technicians must be aware of these procedures' effect on the final color of the restorations.

The minimum thickness of a multilayer ceramic restoration required for masking dark background

Masking dark tooth structure or darkness of oral cavity with ceramic restorations is an important concern. The aim of this study was to determine the minimum thickness of a multilayer all-ceramic restoration (IPS-emax Press) required for a proper masking in these situations. In this experimental in vitro study, 36 multilayer ceramic disks of IPS e.max Press (IvoclarVivadent, Schaan, Liechtenstein) with the diameter of 13 mm were prepared and allocated in six groups of different core/veneer thicknesses: 0.4/0.4 mm (G1), 0.5/0.5 mm (G2), 0.6/0.6 mm (G3), 0.8/0.7 mm (G4), 1.0/0.8 mm (G5), and 1.1/0.9 mm (G6). For backgrounds, the standard black tile of spectrophotometer (B) was used to stimulate the darkness of oral cavity, and an opaque ceramic (OC) of IPS-emax Press (OC) was fabricated to determine the masking ability. CIELAB values of all disks on B and OC backgrounds were measured, and ΔE was calculated between two backings. One-way ANOVA and post hoc tukey test were used to analyze the data. ΔE ≤3.3 and P < 0.05 were considered, respectively, as the clinically acceptable limit and the level of statistical significancy. The mean ΔE between B and OC of groups 4 (2.83 ± 0.80) and 5 (1.46 ± 0.36) were within the range of the clinically acceptable color difference (ΔE ≤3.3); thus these groups could properly mask the black background. A trend was existed in the results as by increasing the thickness, ΔE was decreased. A thickness of 1.5 mm of a multilayer ceramic restoration (IPS e.max Press) is required to mask a dark discoloration.

Effect of different filters on the extraction of norbixin from Bixa orellana for synthetic fiber dyeing and development of a post-dyeing process for removal of the unfixed dye

The aim of this study was to compare the efficiency of three types of filters for the extraction of the annatto dye from Bixa orellana for polyester dyeing. In addition, post-dyeing washing processes were proposed to improve the wash and rubbing fastness. In the extraction procedure the paper filter presented the highest yield (13.3%), followed by the polypropylene (11.4%), but there was no significant difference in the results for the exhaustion percentage (average of 87.4%) and K/S values (1.68 to 2.24). Results showed the polypropylene filter was the most suitable and can be reused. The post-dyeing washing processes with detergent improved the fastness increasing the color transfer score from 1.5 (large change) to 3 (small change). An acceptable color difference between the dyed fabric samples before and after washing was observed. Results indicate that the post-dyeing washing process improves the quality of dyed fabrics to levels acceptable for industrial application.

Comparison of color difference and reliability of two intraoral spectrophotometers

Aim: to evaluate the intra and inter-device reliability of two intraoral spectrophotometers in measuring the Commission Internationale de l’Éclairage (CIE) L*a*b* color coordinates and to compare the color difference (ΔE) between both devices. Methods: the central region of the labial surface of the maxillary central incisor of 31 participants was measured twice by each of the devices (VITA EasyShade and Degudent Shadepilot) by one examiner. CIE L*a*b* color coordinates were obtained for all teeth and ΔE was measured and compared. Intraclass correlation coefficient (ICC) and Mann-whitney U test were used to analyze the data (p&lt;0.05). Results: inter-device reliability ICCs in measuring CIE L*a*b* color coordinates ranged between 0.08-0.49 with significant difference between devices only concerning the b coordinate (p&lt;0.05). While intra device reliability ICCs ranged between 0.86-0.89 for VITA EasyShade and 0.81-0.86 for Degudent Shadepilot. The mean ΔE for CIE L*a*b* color coordinates of VITA EasyShade was 3.61 (±1.93) compared to 3.60 (± 1.45) for Degudent Shadepilot with insignificant difference between both devices (p&gt;0.05). Conclusions: high intra device reliability in measuring CIE L*a*b* color coordinates was achieved particularly of Vita EasyShade, and both devices had clinically acceptable color difference (ΔE &lt;3.7) however, inter device reliability was low to moderate. Consequently, the same spectrophotometer should be used throughout the steps of performing any tooth- colored restoration.

Expanding the color gamut of inkjet textile printing during color matching

AbstractOne of the most important subjects of digital printing is evaluation of color gamut mapping. A printer can only reproduce colors that are in its color gamut. Maybe, a color tolerance between reference sample and printed sample is in agreement between manufacturer and customer. The goal of this work is to estimate the expansion of the color gamut of an inkjet textile printer by consideration of the acceptable (predetermined) color difference during color matching. For analyzing the color gamut, a standard color chart IT8.7/4‐2005 CMYK target was printed by nine different mixtures of CMYK, and then the reflectance spectra and colorimetric parameters of the printed samples were measured. The inks used were disperse water‐based inks that were printed on the polyester fabric. The maximum acceptable color difference in this study was equal to 2 CIELAB units for all colors. In order to estimate the color gamut with the maximum acceptable color difference, for all boundary points of gamut, expanded points were obtained by Euclidean distance less than = 2. The results show that when the acceptable color difference is considered in color gamut measuring, the area and volume of the color gamut are increased and so, the reproducibility of printer is increased. The maximum and minimum expansions of color gamut volumes were obtained by the mixtures with minimum and maximum color gamuts, respectively. The volume expansion of the mixture with the minimum color gamut volume was 34.20%, while the volume expansion of the mixture with the maximum color gamut volume was 28.06%.

Effect of Home Bleaching Agents on Color Stability and Surface Roughness of Hybrid Ceramics: An in vitro study.

To evaluate the effect of two different home bleaching agents on the color stability and surface roughness of hybrid ceramics. Three dental hybrid ceramics (Lava Ultimate, CeraSmart, and Vita Enamic) and two different home bleaching agents (hydrogen peroxide [9.5%; HP] and carbamide peroxide [22%; CP]) were used. Thirty specimens with dimensions of 12 x 14 x 1 mm were prepared for each material. Technical polishing kits were applied to one surface of the specimens for the surface finishing procedure. The color parameters (L*a*b*) of specimens were measured. Three subgroups for each ceramic were determined: control (C), HP, and CP (n = 10 each). After bleaching procedures, the color parameters were remeasured, and color differences (ΔE) were calculated. The surface roughness values of the specimens were detected using a profilometer. Surface analysis was performed with a scanning electron microscope on one specimen from each group. Data were analyzed using two-way analysis of variance and Tukey honest significant difference tests. There was an interaction between material and bleaching agent type (P < .05). The highest ΔE values were observed in the CP groups, and the lowest ΔE values were observed in the C groups. For surface roughness, there was no interaction between material and bleaching agent type (P > .05). Material and bleaching agent factors had a significant effect on surface roughness (P Δ .05). The highest surface roughness values were detected in the HP groups. Home bleaching agents caused clinically acceptable color differences on hybrid ceramic materials. HP increased the surface roughness of hybrid ceramics.

Dope-Dyeing of Polyvinyl Alcohol (PVA) Nanofibres with Remazol Yellow FG.

The lack of aesthetic properties of electrospun nanofibres in terms of colour appearance is the drive in this preliminary study. This research is conducted to study the dyeing behaviour and colorimetric properties of electrospun nanofibres blended with Remazol Yellow FG reactive dye using dope-dyeing method via electrospinning process. This paper reports the colorimetric properties of dyed poly vinyl alcohol (PVA) nanofibres within the range of 2.5 wt.% to 12.5 wt.% dye content. The electrospinning parameters were fixed at the electrospinning distance of 10 cm, constant feed rate of 0.5 mL/h and applied voltage of 15 kV. The resulting impregnated dye of 10 wt.% exhibits acceptable colour difference of dyed PVA nanofibres, with a mean fibre diameter of 177.1 ± 11.5 nm. The SEM micrographs show the effect of dye content on morphology and fibre diameter upon the increment of dye used. Further increase of dye content adversely affects the jet stability during the electrospinning, resulting in macroscopic dropping phenomenon. The presence of all prominent peaks of Remazol dye in the PVA nanofibers was supported with FTIR analysis. The addition of dye into the nanofibres has resulted in the enhancement of thermal stability of the PVA as demonstrated by TGA analysis.

Reuse of enzymatically treated reactive dyeing baths: Evaluation of the number of reuse cycles

Processing of textiles, especially dyeing, demands large quantities of water, generating huge amounts of effluents. A sustainable strategy to reduce the volume of textile effluents is treatment and reuse of the residual liquid waste. The aim of this study was to evaluate the number of reuse cycles of residual dyeing baths from reactive cotton dyeing treated with horseradish peroxidase. The enzymatic treatment achieved a 99% color removal permitting further reuse. Despite of the high decolorization efficiency residual impurities in the decolorized dyeing baths interfered negatively in cotton dyeing results with reactive dyes, and further dilution was found to be necessary. The best results were obtained with dilution rates of 70, 80 and 90% with distilled water, attaining acceptable color differences (ΔE) of 0.94, 0.73 and 0.52, respectively. These values could be maintained throughout ten reuse cycles, providing a water economy up to 30% per dyeing. Furthermore, the colored washing liquors originating from the post-dyeing washing steps received the same enzymatic treatment and could be reused in the same reactive dyeing procedures at a dilution of 90% with distilled water, providing ΔE values of 0.3–0.7. Furthermore, the reuse of enzymatically treated post-dyeing washing liquors was evaluated in the same reactive dyeing procedures. Similar decolorization was observed and reuse at 90% dilution was feasible. Without considering the reuse of the residual liquor of the washing step, 10–30% of water could be saved, which means per batch of 200 kg of cotton fabric, water savings of about 200–600 L.

Effect of spray drying compartment and maltodextrin concentration on the functional, physical, thermal, and nutritional characteristics of Bambara groundnut milk powder

The study examined the effect of drying compartment and maltodextrin concentration on the functional properties of Bambara groundnut milk powder (BGNMP). Bambara groundnut milk (BGNM) was prepared from Bambara groundnut (BGN) flour and water, further processed into BGNM and dried using the spray drying process. Total solids of BGNM were increased with 5, 10, and 15% of maltodextrin. Functional properties of BGNMP were analyzed. Water absorption indices (WAI), wettability, and water solubility indices (WSI) ranged from 0.19 to 0.45 g/g, 136.8 to 292.4 s, and 85.18 to 90.25%, respectively. BGNMP (10%) was significantly (p < .05) higher in WSI (88.80%) compared to BGNMP with 5% maltodextrin. BGNMP (10%) was significantly higher (p < .05) in WAI (0.40 g/g) compared to BGNMP with 15% maltodextrin. BGNMP samples color characteristics were significantly (p < .05) different with an acceptable color difference (ΔE). BGNMP (10%) had acceptable hydration properties over BGNMP (5%, 15%). Practical applications Bambara groundnut (BGN) is underutilized, stated to have little economic importance. However, recent studies have proven BGN to be promising in improving food security through research, resulting in food product (milk, yoghurt, fiber) development. Milk from BGN has been reported with acceptable physical attributes and comparable to existing plant milk. However, nothing has been reported on BGN milk powder (BGNMP). The development of BGNMP will promote the use of BGN. This will result in the social development of the country, by creating job opportunities for woman farmers and improve lives of individuals and providing gender empowerment. The success of this study will also provide food nutrition, security, and sustainability, as BGN is nutritious, widely, and readily available throughout Africa regions. Expanded utilization of BGN will encourage its production (harvesting) resulting in exporting of the material, improving the country's economy by opening up new and improved investment opportunities and new markets.

Energy-Saving Light Source Spectrum Optimization by Considering Object's Reflectance

When an object is illuminated, part of the incident light is absorbed by the object that does not contribute to the illumination. If the light source's spectrum can be optimized by decreasing the light energy along the absorbed wavelengths, substantial energy can be saved. In this study, a spectrum optimization method by means of a genetic algorithm to minimize the light energy along the absorbed wavelengths while maintaining the light quality of the light source was proposed. Under the constraint that the color differences of the object illuminated by the optimized illuminant and the reference illuminant do not exceed specified levels, maximum energy saving ratio (ESR) is achieved for various reference illuminants. It is found that through the proposed method effectively saving the energy, for a monochromatic object, the ESR can reach 49.5% with barely recognizable color difference, whereas for a polychromatic object, the ESR can reach 55.2% with an acceptable color difference for each patch of the object.

The Use of Resin Composite Layering Technique to Mask Discolored Background: A CIELAB/CIEDE2000 Analysis.

The purpose of this study was to evaluate the ability of three resin composite systems to mask a severely discolored background by the application of a layering technique through CIELAB and CIEDE2000 analysis. Ninety 1.5-mm-thick disc specimens were produced from three different resin composite restoration systems: IPS Empress Direct (Ivoclar Vivadent), Charisma Diamond (Heraeus Kulzer), and Filtek Z350 XT (3M-ESPE). The specimens were divided into groups according to the restoration system and the resin composite shade combination used for the layering technique (enamel, body, and dentin shades). Color measurements were performed by a reflectance spectrophotometer (SP60, EX-Rite) against a C4 shade background and an inherent color background, which simulates a severely discolored background and a tooth surface with no discoloration, respectively. The total color difference between both color measurements was calculated by CIELAB (ΔE*ab) and CIEDE2000 (ΔE00) formulas. The mean ΔEab* and ΔE00 values were analyzed by analysis of variance (general linear models) and Tukey's post hoc tests (α=0.05). Three groups presented clinically acceptable color difference values (ΔE*≦3.46 and ΔE00≦2.25): 1.5 mm dentin, 1.0 mm dentin/0.5 mm body, and 1.0 mm dentin/0.5 mm enamel; ie, all the groups from the Z350 XT restoration system. The resin composite layering technique is an effective way to mask severely discolored backgrounds. The Filtek Z350 XT system was the only restoration system capable of masking the C4 background.

In vitro comparison of instrumental and visual tooth shade determination under different illuminants

Statement of problemWhile a considerable body of literature deals with the comparison between visual and instrumental tooth color determination, in most of these studies either the number of color specimens or the number of examiners is too small to allow for a general statement about such a subjective method as visual color determination. Furthermore, perceptual aspects like perceptible or acceptable color differences are often not considered. PurposeThe purpose of this study was to investigate the precision of a spectrophotometer in tooth shade determination compared with visual color matching using a shade guide in vitro. Moreover, the influence of different illuminants as well as of sex and professional experience of the examiners on visual color matching was analyzed. Material and methodsFifty examiners (13 men, 37 women; without dyschromatopsia), grouped by professional experience, determined the shades of 10 prosthetic teeth with the Vitapan classical shade guide under 4 illuminants (daylight, halogen, fluorescent [5000 K], fluorescent [nonspecific ceiling light]) and with a spectrophotometer (Shadepilot). Reproducibility (precision) of color determination was characterized by the average of the highest percentages of interexaminer agreement for each specimen. Additionally, color differences (ΔE) were calculated based on CIELab values. ResultsThe mean reproducibility of the spectrophotometer was 92.2%, while for visual examination it was 43.7%. The corresponding differences in CIELab color space amounted to ΔEinstr=2.6 and ΔEvis=5.2. Illuminants and professional experience showed a significant influence, while sex did not. ConclusionWhile the spectrophotometer provided higher reproducibility, considering the color differences, the results obtained by visual inspection were still satisfactory. The differences due to type of illuminant, degree of experience, and sex of the examiners are of little practical relevance.

The minimum thickness of a multilayer porcelain restoration required for masking severe tooth discoloration.

Although studies have shown that porcelain veneers are very efficient for treating discolored teeth, they did not address in particular the minimum thickness of a multilayer IPS e.max Press (IvoclarVivadent, Schaan, Liechtenstein) restoration required to mask discolored tooth. The aim of this study was to determine the minimum thickness of a multilayer porcelain restoration required for masking severe tooth discoloration. A total of 24 disk-shaped multilayer specimens were prepared from IPS e.max Press with the diameter of 13 mm and four different thicknesses (core/veneer: 0.4/0.4 mm, 0.5/0.5 mm, 0.6/0.6 mm and 0.8/0.7 mm). Two backgrounds, C4-shade body porcelain and an opaque background from the selected IPS e.max ceramic itself were fabricated to mimic a discolored or stained natural tooth structure and to determine the masking ability. After applying the resin cement layer (Panavia F2.0) with 0.01 mm thickness on each background, all specimens were measured on both background using a spectrophotometer and values of L*, a* and b* were calculated to determine the color differences (ΔE*ab). One-way ANOVA and post-hoc tests of specimen average one-to-one comparison (Tukey HSD) were conducted and P ≤ 0.05 was set as the level of significance. ΔE*ab of all groups were within the range of the clinically acceptable color difference (ΔE≤3.3), thus all the groups could mask the C4 background even group 1 with only 0.8 mm thickness. A trend was shown in the results as by increasing the thickness, ΔE*ab is was decreased. The mean ΔE*1*a*b between different thicknesses were statistically significant (P < 0.05) only between group 4 with groups 1 and 2, respectively. Within the limitations of this study, all studied thicknesses could mask the C4 background. However, the minimum thickness of a multilayer porcelain restoration (IPS e.max Press) required for masking severe tooth discoloration was 0.8 mm.

Study of an Acceptable Color-Difference Formula of Printed Documents

Study of an Acceptable Color-Difference Formula of Printed Documents

The effectiveness of four methods for stain removal from direct resin-based composite restorative materials.

Few studies investigated the best method for removing stains from different types of resin-based composite restorations and compared them to the more recently introduced nanocomposites. This study compared the effect of four methods for stain removal from composite resins; finishing with Sof-lex disks, using pumice and brush, bleaching with 10% carbamide peroxide and 38% hydrogen peroxide. Twenty disk specimens were prepared. Specimens were immersed in a staining solution for 3weeks. The stained surfaces of five specimens from each RBC material were treated with one of the treatment procedures. Colorimetric measurements were taken using spectrophotometer prior to and after staining, and then repeated after surface treatments. Color difference values were calculated. One-way ANOVA indicated significant differences in color change of the three composite resin materials following staining. Filtek Z250 showed the least susceptibility to discoloration followed by Renamel, Filtek Supreme was the material most prone to discoloration. Two-way ANOVA and Tukey's Post Hoc showed that all stain removing procedures except polishing with pumice, were able to return Filtek Z250 to clinically acceptable color difference. While bleaching with 38% carbamide peroxide was not effective with Renamel. Only pumice and 10% carbamide peroxide were able to return Renamel to clinically acceptable color difference. Compositions of resin-based composite resins play an important role in their susceptibility to stain and their amenability to stain removal procedures. Home bleaching showed good results for the three materials, while office bleach was the least effective.