Effects of Organic Based Heat Stabilizer on Properties of Polyvinyl Chloride for Pipe Applications: A Comparative Study with Pb and CaZn Systems

In this paper, the effects of organic based stabilizers (OBS) are investigated and compared with traditional lead (Pb) and calcium zinc (CaZn) heat stabilizers regarding their processability, mechanical property, and thermal degradation behaviors in rigid PVC pipe applications. In addition, the effects of repeated processing cycles on the degree of gelation and the impact strength of the PVC/OBS, PVC/CaZn, and PVC/Pb are also examined. A repeated processing cycle of those three types of the heat stabilizers up to four cycles was found to increase the degree of gelation and proved no significant effect on the impact strength and heat resistance of the resulting PVC samples. The OBS showed a positive effect on preventing the autocatalytic-typed thermal degradation of the PVC samples. This leads to a longer retention time for the initial color change of the PVC/OBS compared to PVC/Pb or PVC/CaZn systems. This characteristic was related to a more uniform fusion behavior of the PVC/OBS, i.e., the lowest gelation speed and the longest fusion time. The non-isothermal kinetic parameter determined by the Kissinger and Flynn–Wall–Ozawa methods of the dehydrochlorination stage of the PVC/OBS was in satisfactory agreement and continued to compare with the PVC/Pb and PVC/CaZn systems. The results indicated that the OBS might decrease the dehydrochlorination rate of PVC, implying that PVC/OBS was more stable than PVC/Pb and PVC/CaZn systems.

Influence of Resin Cements and Ceramic types on the Color Stability and Translucence of Laminate Veneers/ Influência dos Cimentos de Resina e Tipos Cerâmicos na Estabilidade da Cor e Translucidez das Facetas Laminadas

Objective: This study evaluated the color stability and translucence of resin cements in the fixation of ceramic veneers submitted to aging protocols. Material and Methods: Buccal faces of bovine incisors were planed up to dentin. Eighty ceramic veneers (1 mm) were prepared using two pressed ceramics (IPS e-maxPress and IPS e-maxZirpress, IvoclarVivadent). Before the initial color and translucence readouts (Vita EasyShade, VITA), the veneers were fixed with light (Variolink II, Ivoclar/Vivadent) or dual cured (Relyx U200, 3M ESPE) cements. The samples were submitted (n=10) to thermal mechanical cycling (1.200.000 cycles, 1,3Hz, 5°C/37°C/55°C); and no aging protocol (control). New color and translucence readouts were performed. The cement thickness was quantified by a double coordinate stereomicroscope (Nikon Measurescope) as a control of the study. Results: Data (3-way ANOVA, Tukey, p0,05) showed difference (p0.05) in the color change for both ceramics cemented with U200 with no aging protocol. In the other groups, there was no significant difference (p0.05). There was no difference for translucence regardless ceramics, cements, or aging protocol. Thermal mechanical cycling was not significant for optical changes of the ceramics tested. Conclusions: It was concluded that the color stability and translucence of ceramics with thickness of 1mm were not influenced by the cement when submitted to thermal mechanical cycling.

Colorimetric Comparison of Internal Bleaching with and without Removing Mineral Trioxide Aggregate (MTA) on Induced Coronal Tooth Discoloration by MTA

Objective. This study aimed to colorimetric comparison of internal bleaching with and without removing mineral trioxide aggregate (MTA) on induced coronal tooth discoloration by MTA cement. In this experimental study, twenty human teeth were prepared. An OrthoMTA barrier was placed 1 mm below the CEJ. The teeth were restored with composite resin and were placed in the aging accelerator machine. Then, the specimens were divided into two groups (n = 10); in group A, part of the OrthoMTA was removed and the glass ionomer was placed on the OrthoMTA, and in group B, the OrthoMTA remained intact. Internal bleaching was performed 5 times in 6-day intervals using 37% carbamide peroxide gel. Color determination was performed in 5 stages: baseline, after OrthoMTA discoloration, before OrthoMTA removal, after OrthoMTA removal, and after bleaching treatment sessions. In group A, 8 specimens reached to ∆E < 3.3 after 2 times internal bleaching treatment, and in group B, 5 specimens reached to ∆E < 3.3 with almost 3 bleaching sessions p > 0.05 . Additionally, 5 specimens reached to the initial color (baseline) after bleaching treatment, 4 specimens in group A and 1 specimen in group B. After OrthoMTA removal, 2 specimens in group A reached to ∆E < 3.3. There was no significant difference between groups with or without OrthoMTA removal p = 0.06 . Although, the specimens with OrthoMTA removal required fewer bleaching treatment sessions, and the mean value of ∆E was lower in this group.

Color Stability and Surface Roughness of Hybrid and Nanofilled Composites Brushed with Abrasive Dentifrices

The aim of this study was to evaluate the color stability and the surface roughness of different composites brushed with toothpastes presenting different levels of abrasivity. Thirty discs of each material were obtained using michohybrid composites (Brilliant NG and Charisma Diamond) and a nanocomposite (Filtek Z350XT). The initial color (CIELab) and surface roughness (confocal laser scanning microscopy) of resin discs were evaluated. Afterwards, 10 specimens per group were brushed with the following dentifrices: Maximum Cavity Protection, Sensodyne Repair & Protect and Colgate Sensitive Pro-Relief. Brushing was performed with an electric toothbrush equipped with soft bristle head, with standard power and weight, for 30 minutes. Every 30 seconds, 1.0 ml of the slurry was injected between the bristles of the brush and the specimen. After abrasive challenge, the samples had their color and roughness reevaluated. Data were submitted to the Kruskal-Wallis test (color change) or the t-test (surface roughness). The level of significance was 5%. Results: Brushing did not significantly change the color of the composites tested in the study herein . On the other hand, the surface roughness of the composites was significantly affected by the abrasive challenge, regardless of the toothpaste used. The surface roughness change was similar for all the composites. The abrasive challenge with the toothpastes Maximum Cavity protection, Sensodyne Repair & Protect and Colgate Sensitive Pro-Relief was not able to significantly change the color of the composite resins. Nevertheless, the abrasive challenges significantly altered the surface roughness of all the evaluated composites. However, the changes in surface roughness were statistically similar in the microhybrid and nanofilled composites. Keywords: Composites Resins. Dentifrices. Color. ResumoO objetivo deste estudo foi avaliar a estabilidade de cor e a rugosidade superficial de diferentes resinas compostas escovadas com dentifrícios de diferentes níveis de abrasividade. Trinta discos de cada material foram obtidos utilizando compósitos micro-híbridos (Brilliant NG e Charisma Diamond) e um nanocompósito (Filtek Z350XT). A cor inicial (CIELab) e a rugosidade superficial (microscopia confocal de varredura a laser) dos discos de resina foram avaliadas. Em seguida, 10 amostras por grupo foram escovadas com os dentifrícios Máxima Proteção Anticáries, Sensodyne Repair & Protect e Colgate Sensitive Pro-Alívio. A escovação foi realizada com uma escova elétrica com cabeça de cerdas macias, com potência e peso padronizados, durante 30 minutos. A cada 30 segundos, 1,0 ml da pasta era injetada entre as cerdas da escova e a amostra. Após o desafio abrasivo, as amostras tiveram sua cor e rugosidade reavaliadas. Os dados foram submetidos ao teste de Kruskal-Wallis (alteração de cor) ou ao teste t (rugosidade da superfície) (α=5%). A escovação não alterou significativamente a cor dos compósitos. Por outro lado, a rugosidade superficial dos compósitos foi significativamente afetada pelo desafio abrasivo, independentemente do dentifrício utilizado. A alteração da rugosidade superficial foi semelhante para todos os compósitos. O desafio abrasivo com a Máxima Proteção Anticáries, o Sensodyne Repair & Protect e o Colgate Sensitive Pro-Alívio não foi capaz de alterar significativamente a cor das resinas. Diferentemente, os desafios abrasivos alteraram significativamente a rugosidade superficial de todos os compósitos avaliados. No entanto, as mudanças na rugosidade foram estatisticamente semelhantes nos compósitos micro-híbridos e nanoparticulado. Palavras-chave: Resinas Compostas. Dentifrícios. Cor.

Comparison of the Effect of 0.2% Chlorhexidine Mouthwash and Persica Mouthwash on the Color of Resin Composite

Introduction: Discoloration of resin composite restorations can lead to patient dissatisfaction. 0.2% Chlorhexidine and Persica mouthwashes are among the agents that cause discoloration. The aim of this study was to investigate the degree of discoloration caused by the 0.2% Chlorhexidine and Persica mouthwashes on resin composite samples. Materials and Methods: This in-vitro experimental study was conducted in Kashan and Isfahan School of Dentistry in 2020-2021. Number of 30 disc-shaped samples were fabricated from Charisma Diamond resin composite. The initial color of samples was measured by CIE Lab system in spectrophotometer. Then samples were divided into 3 groups (A, B, and C) (n = 10).The control group (A) was placed in distilled water, group B was immersed in the 0.2% Chlorhexidine mouthwash and group C was immersed in the Persica mouthwash. The color of the samples was measured again afterwards. Data were analyzed with One-way ANOVA and t-Test (α = 0.05). Results: The amount of l, a, b and ΔE after using 0.2% Chlorhexidine and Persica mouthwashes increased. The mean of Δl, Δa, Δb and ΔE showed significant differences between groups (p value < 0.05). Conclusion: The discoloration of Persica mouthwash was more than 0.2% Chlorhexidine mouthwash and control group. Therefore, for patients with resin composite restorations, 0.2% Chlorhexidine mouthwash is better.

Can the efficacy of in-office tooth bleaching change in the presence of orthodontic brackets? An in vitro study

Objective: To assess the color change of bovine enamel after tooth bleaching while using orthodontic brackets. Methodology: This in vitro study selected 48 bovine incisors without visible fractures or cracks (cut in blocks of 8x12x3 mm). They were distributed in four groups: no staining and with brackets (NSWB), no staining and no brackets (NSNB), with staining and brackets (WSWB), and with staining and no brackets (WSNB) (n=12). The color was initially assessed with a spectrophotometer for NS (no staining). The teeth in WS (with staining) groups were immersed in an instant coffee solution for 15 days and the initial color was also assessed. After prophylaxis and adhesive treatment, the brackets were bonded to the teeth. The teeth were bleached with 35% hydrogen peroxide and the color was analyzed 30 days after bleaching. A two-way Analysis of Variance was applied as well as a subsequent multiple comparison analysis (p>0.05). Results: According to the data obtained, the factor of the presence of brackets (p=0.569) had no significant influence. This differed from the factor of tooth staining (p<0.001). Moreover, there was no interaction between them (p=0.863). Conclusion: The presence of brackets in non-stained teeth did not affect bleaching effectiveness. The ΔE of stained teeth was always lower than non-stained teeth, especially for the NB (no brackets) group.

Study on the effect of heat treatment on amethyst color and the cause of coloration

The effect of heat treatment on amethyst color was studied from a new perspective of chromaticity of gemstones and the cause of amethyst coloration was discussed based on the results of X-ray diffraction, ultraviolet–visible spectroscopy. The results show that the amethyst color has no significant relationship with cell parameters but the crystallinity index decreases as temperature rises. The absorption band at 545 nm in the UV–visible spectrum can be related to a charge-transfer transition of Fe3+ and O2−, which has a significant relationship with amethyst lightness and chroma. The color at different temperatures can be divided into three stages: The amethyst stage with temperature below 420 °C, the prasiolite stage with temperature between 420 and 440 °C where the color center is the most unstable, the citrine stage with temperature above 440 °C. The color change degree of heated amethyst is related to its initial color. When the initial color is darker, the color difference of heated amethyst is larger, and the easier it is to change the color after heat treatment. A more appropriate heating temperature to obtain citrine by heating amethyst is about 560 °C.

First Results from a Panchromatic HST/WFC3 Imaging Study of the Young, Rapidly Evolving Planetary Nebulae NGC 7027 and NGC 6302

We present the first results from comprehensive, near-UV-to-near-IR Hubble Space Telescope Wide Field Camera 3 (WFC3) emission-line imaging studies of two young planetary nebulae (PNe), NGC 7027 and NGC 6302. These two objects represent key sources for purposes of understanding PNe shaping processes. Both nebulae feature axisymmetric and point-symmetric (bipolar) structures and, despite hot central stars and high nebular excitation states, both harbor large masses of molecular gas and dust. The sweeping wavelength coverage of our Cycle 27 Hubble Space Telescope (HST)/WFC3 imaging surveys targeting these two rapidly evolving PNe will provide a battery of essential tests for theories describing the structural and chemical evolution of evolved star ejecta. Here, we present initial color overlays for selected images, and we highlight some of the first results gleaned from the surveys.

Basic Mathematics of Color Space Invariants

Color management in printing processes has been traditionally based on an analysis of the behavior of tone reproduction curves (TRC) calculated for the initial color channels. The tone curves, as well as, the color channels, are considered separately. This approach does not take into account the mutual influence of colorants when they overlap. We propose replacing two-dimensional tone reproduction curves with three-dimensional gradation trajectories in the CIE Lab metric space. When two colors overlap, one considers the space between two gradation trajectories that forms a gradation surface. These objects are described using the apparatus of differential geometry of spatial curves and surfaces, respectively, and are also invariants of color spaces. In this paper, we offer their analytical description.

Color removal efficiency of rice husk biochar modified with magnetized iron oxides and nano zero valent iron for decolorization of dyeing wastewater

Rice husk biochar, a rich-carbon material, can be modified with other reactive elements to improve its original properties for organic-contaminant removal efficiency. In this study, rice husk was heated to 600 oC without air in a closed-furnace for producing the rice husk biochar (BC600). BC600 was then magnetized for making an intermediate magnetized rice husk biochar (BC600-mag). Finally, nano zero valent iron (nZVI) was synthesized on BC600-mag for producing magnetized biochar impregnated nZVI (BC600-mag-nZVI). Batch experiments were conducted to investigate color removal efficiency of BC600-mag-nZVI for the reactive dyes yellow (RY145), red (RR195) and blue (RB19) from dyeing solutions with the initial color concentrations of approximately 400 Pt-Co. Results showed that, for RY145 and RR195, the optimum color removal efficiency (ɳopt) achieved the values of 95 and 93% at doses of 0.50 and 1.50 kg BC600-mag-nZVI/m3 dyeing solution, according to the treated color decreased to 21 and 30 Pt-Co, respectively, which are lower than the allowable discharged standard of column A (≤ 50 Pt-Co) of QCVN 40:2011/BTNMT, while for RB19, the ɳopt achieved the values of 63 % at dose of 8.00 kg BC600-mag-nZVI/m3 dyeing solution, according to the treated color decreased to 147 Pt-Co which is lower than the allowable discharged standard of column B (≤ 150 Pt-Co) of QCVN 40:2011/BTNMT. In addition, with increasing dose of the modified biochars, the color removal efficiency increased accordingly, achieving almost 100% for RY145 and RR195 and over 70% for RB19. It is concluded that the magnetic-nZVI rice husk biochars effectively removed the reactive dyes. In the other hand, the impregnation of nZVI particles on the biochar backbone spatially separates the particles, prevents their aggregation and therefore enhances their reactivity This study therefore proposes a new application of rice husk biochar modified with magnetized iron oxides and zero valent iron decolorization of dyeing wastewater.