Does Bleaching Affect the Microleakage of Class II Restoration with Bulk-Fill Composite?

Introduction. The use of technology in bulk-fill composites (BCs) has reduced the stresses caused by polymerization shrinkage, debonding, microleakage, or posttreatment sensitivity in them. This study was conducted to determine whether bleaching affects the microleakage of class II restoration with bulk-fill material. Materials and Methods. This laboratory study was performed on 40 normal human premolars in 4 groups (n = 20). Class II cavities were prepared in mesial and distal surfaces of the teeth with dimensions of 2 × 2 × 4 mm. Then, based on the bleaching process by 20% carbamide peroxide gel and using two types of composites, the restored cavities were randomly divided into 4 groups: (1) CC without bleaching (CC group), (2) BC without bleaching (BC group), (3) CC with bleaching (CCB group), and (4) BC with bleaching (BCB group). Then, the samples were thermocycled for 1000 cycles at a temperature range of 5–55°C, and they were immersed in 0.6% alkaline fuchsine in order to penetrate into the pigment for 24 h. After cutting, the samples were placed under a stereomicroscope (40%) to determine microleakage. The data were analyzed using one-way analysis of variance (ANOVA), and a p value <0.05 was considered as statistically significant. Results. Microleakage was determined in the CC group 0.97 ± 0.42 , BC group 1.08 ± 0.54 , CCB group 1.19 ± 0.37 , and BCB group 0.30 ± 0.47 . There were also no significant differences in the mean microleakage between the groups. No cases with zero microleakage (no microleakage) and grade 3 of microleakage (pigment penetration into the axial wall) were observed in the samples. Also, a two-by-two comparison of significant differences between CC and BC groups p = 0.89 , CC and CCB groups p = 0.45 , CC and BCB groups p = 0.11 , BC and CCB groups p = 0.87 , BC and BCB groups p = 0.41 , and CCB and BCB groups p = 0.86 showed that the difference was not statistically significant. Conclusion. Results showed no difference between microleakage of BC and CC with and without bleaching, and bleaching had the same effect on microleakage of these two types of composites.

Sintesa dan Karakterisasi Biofuel dari Limbah Laboratorium Teaching Factory Politeknik Negeri Lhokseumawe dengan Proses Catalytic Cracking

Spent earth is a waste resulting from the bleaching process which contains gums and a large amount of oil so that it still has the potential to be reprocessed into biofuel. This study aims to utilize the oil from spent earth as a raw material in the synthesis of biofuels through the catalytic cracking process. In the catalytic cracking process, zeolite and kaolin catalysts are used in the ratio (0:100); (30:70); (50:50); (70:30) and (100:0) and temperature variations of 150oC, 175oC and 200oC for 3 hours. Based on the research results, the best biofuel was obtained at a catalyst ratio of zeolite: kaolin (70:30) and a temperature of 200oC with a yield of 76.13%. The results of the biofuel characterization obtained a water content of 0.0301%, octane number 90.5 RON and a density 751 kg/m3. Analysis of biofuel composition was measured using GC-MS and it was found that the biofuel contained 4.60% C11H24, 8.99% C12H26, 22.49% C16H34, 9.54% C18H34O2 and 54.38% C19H36O3. Based on the physical and chemical properties of the biofuel as a result of cracking with zeolite and kaolin catalysts, it is in accordance with SNI for gasoline qualification.

Investigation on the Preparation of Rice Straw-Derived Cellulose Acetate and Its Spinnability for Electrospinning

Rice straw-derived cellulose (RSC) with purity of 92 wt.% was successfully extracted from rice straw by a novel and facile strategy, which integrated the C2H5OH/H2O autocatalytic process, dilute alkali treatment and H2O2 bleaching process. Influencing factors of the cellulose extraction were systematically examined, such as ethanol concentration, alkali concentration, H2O2 bleaching process and so on; the optimal extraction conditions of cellulose was determined. A series of rice straw-derived cellulose acetate (RSCA) with different degree of substitution (DS) were prepared by the acetylation reaction; the effects of Ac2O/cellulose ratio, reaction temperature and reaction time on the acetylation reaction were investigated. Results of FTIR and XRD analysis demonstrated that highly purified RSC and RSCA were prepared comparing with the commercial cellulose and cellulose acetate. Solubility analysis of RSCA with different DS indicated as-prepared RSCA with DS of 2.82 possessed the best solubleness, which was suitable for electrospinning. Moreover, the flexible RSCA fibrous membrane was easily fabricated by a facile electrospinning method. Our proposed method provided a strategy for realizing the high-value utilization of waste rice straw resource, as prepared RSC and RSCA can be used as chemical raw material, and electrospun RSCA fibrous membrane has various applications in medical materials, food packaging, water purification and so on.

Influence of blenching agents on the mechanical properties and colour of dental restorative nanocomposite

Purpose: Bleaching agents are commonly used to make the natural dentition look more attractive. Currently, in addition to products from reputable manufacturers, products of not fully known origin are available for purchase. The aim of the study was to investigate whether products of this type have a destructive influence on the mechanical and aesthetic properties of the dental restorative nanocomposite. Design/methodology/approach: Four bleaching agents were used, two recognized brands, and two products were purchased from Chinese websites (their manufacturer is unknown). Two gels and two types of whitening strips were used. One composite nanomaterial was used. Microhardness, diametral tensile strength,, compressive strength and colour measurements were tested. Findings: For some bleaching agents, studies have shown a relatively small effect on mechanical properties and an acceptable effect on colour changes. Regardless of the observed changes, the use of bleaching agents qualified for the experiment should be considered safe for composites. Research limitations/implications: The number of blenching agents used as well as dental composites in this study was limited. In future studies, increasing the number of cycles in the bleaching process should be considered. Practical implications: A popular method of improving the aesthetic properties of teeth is the use of a wide range of blenching agents. Most patients who use teeth whitening procedures are also users of composite fillings. The use of bleaching agents may have a different effect on the mechanical and aesthetic restorative composites. For economic reasons, many people decide to import cheap bleaching agents of unknown or dubious origin via Internet services to perform the bleaching process on their own. In this study, it was investigated whether products of this type have an influence on the mechanical and aesthetic properties of the dental restorative nanocomposite. Originality/value: Until now, no comparison of the safety of the use of bleaching agents of recognized manufacturers and of unknown origin in terms of the effect on composite materials has been presented, despite their high social importance.

H2O2 bleaching of brown pulp with adsorbed xylan and its modifying effects on the mechanical properties of paper

Xylan is the primary hemicellulose in most hardwood species, especially in birch. Research has highlighted the exploitation of xylans as a strength-enhancing additive to paper due to the current trend for the effective utilization of biomass. In this paper, a new pulping process was proposed, which involved the extraction of xylan prior to pulping, followed by the re-adsorption of the pulp after the final stage in the digester, followed by a suitable bleaching process. The aim of this work was to bleach hardwood kraft pulp (brown pulp) with adsorbed birch xylan via hydrogen peroxide and study the effect of the bleaching parameters on the paper properties. The results showed that the optical properties of paper decreased; however, the mechanical properties increased after the brown pulp adsorbed birch xylan. During the bleaching process, better mechanical properties were obtained with shorter bleaching times and lower bleaching temperatures, initial pHs, and MgSO4 dosages. However, the optical properties were improved as the bleaching time, temperature, initial pH, and MgSO4 dosage were increased. The adsorption of birch xylan could effectively modify the mechanical properties of paper made from brown pulp under various phases.

Least Square Support Vector Regression-Based Model for Whiteness Index of Cotton Fabric Prediction

The textile bleaching process uses a hydrogen peroxide (H2O2) solution in alkali pH associated with high temperature is the commonly used bleaching procedure in cotton fabric manufacture. The purpose of the bleaching process is to remove the natural colour from cotton to obtain a permanent white colour before dyeing or shape matching. Normally, the visual ratings of whiteness on the cotton are measured by the whiteness index (WI). Notice that lesser research study is focusing on chemical predictive modelling of the WI of cotton fabric than its experimental study. Predictive analytics using predictive modelling can forecast the outcomes that can lead to better-informed cotton quality assurance and control decisions. Up to date, limited study applying least square support vector regression (LSSVR) based model in the textile domain. Hence, the present study was aimed to develop the LSSVR-based model, namely multi-output LSSVR (MLSSVR) using bleaching process variables to predict the WI of cotton. The predictive accuracy of the MLSSVR model is measured by root mean square error (RMSE), mean absolute error (MAE), and the coefficient of determination (R2), and its results are compared with other regression models including partial least square regression, predictive fuzzy model, locally weighted partial least square regression and locally weighted kernel partial least square regression. The results indicate that the MLSSVR model performed better than other models in predicting the WI as it has 60–1209% lower values of RMSE and MAE as well as it provided the highest R2 values which are up to 0.9985.