Conventional Bleaching Research Articles

Clinical Evaluation of Different Delivery Methods of At-Home Bleaching Gels Composed of 10% Hydrogen Peroxide.

This study aimed to compare the tooth sensitivity, gingival irritation, and bleaching efficacy of at-home whitening performed with 10% hydrogen peroxide (HP) using a conventional tray-delivered system or two different bleaching systems (strips or prefilled disposable trays). Sixty patients, with maxillary incisors darker than A2 were selected for this single-blind, parallel randomized clinical trial. Teeth were bleached during 14 days with a 30-minute gel contact with teeth per day. The 10% HP was delivered in a bleaching tray (White Class, FGM) in strips (White Strips, Oral-B) or prefilled disposable trays (Opalescence Go, Ultradent). The color changes were evaluated by subjective (Vita Classical and Vita Bleachedguide) and objective (Easyshade Spectrophotometer) methods at baseline and 30 days after the second bleaching session. Tooth sensitivity was recorded during 14 days with a five-point numeric rating scale (NRS) and 0-10 visual analog scale (VAS). The risk of gingival irritation was also recorded during 14 days on a dichotomous scale. All data were submitted to appropriate statistical analysis (α=0.05). No significant difference was observed in the risks of tooth sensitivity among groups ( p>0.09). However, the conventional bleaching tray produced a higher intensity of tooth sensitivity when compared with the strips and prefilled disposable tray systems ( p<0.04). Regarding gingival irritation, the prefilled disposable tray system showed a lower risk of gingival irritation when compared with the conventional bleaching tray ( p=0.003). Significant whitening was observed in all groups after 30 days of clinical evaluation with no significant difference between them ( p>0.06). All 10% HP bleaching systems showed similar whitening after a 14-day use. However, the strips and prefilled disposable trays produced lower intensity of tooth sensitivity than the conventional bleaching tray system. The prefilled disposable tray produced lower risk of gingival irritation when compared to the conventional bleaching tray.

Waterless bleaching of knitted cotton fabric using supercritical carbon dioxide fluid technology

Cotton fiber is the most widely produced and utilized natural fiber with a popular usage in our planet. A substantial amount of clean water is utilized during conventional cotton fiber pretreatment. In this study, we investigated the bleaching possibility of knitted cotton fabric by using supercritical carbon dioxide as a medium, as a cleaner waterless alternative, at pressures in the range of 180 and 250 bar and at temperatures ranging from 80 °C (at the pressure of 180 bar with 505 kg/m3) to 120 °C (at the pressure of 250 bar with 539 kg/m3) for 20 min with either solely hydrogen peroxide usage at 5% and 15% concentrations or combination usage of hydrogen peroxide with necessary related auxiliaries such as peroxide stabilizer at 1% and 8% concentrations and caustic soda at 3% concentration in comparison with conventional aqueous hydrogen peroxide bleaching process in order to support environmentally friendly, sustainable textile production leading to more sustainable future for our planet. Also, the effects of different washing types as after-treatment process following waterless and aqueous peroxide bleaching processes on the whiteness performance of cotton fabrics were also explored. Whiteness properties, moisture management performances, oxycellulose formation and FTIR (ATR) spectra of cotton fabrics bleached in aqueous and waterless supercritical carbon dioxide (scCO2) medium were determined and compared. In waterless scCO2 media, bleaching at 80 °C resulted in higher whiteness improvement than bleaching at 120 °C leading to whiter appearance. Bleaching of cotton cellulosic fiber at 80 °C for 20 min in scCO2 media displayed better whiteness results than conventional water based bleaching at 80 °C. The inclusion of caustic soda in waterless scCO2 hydrogen peroxide bleaching process resulted in significant decline on whiteness level of cotton for both 80 °C and 120 °C bleaching temperatures. When the aqueous conventional bleaching process and the anhydrous (waterless supercritical carbon dioxide fluid) bleaching process compared in the case of solely hydrogen peroxide usage at both 80 °C and 120 °C, waterless supercritical carbon dioxide fluid bleaching process (whether or not after-treated following the bleaching process) resulted in higher whiteness values leading to whiter appearance. Bleaching process with solely 5% and 15% hydrogen peroxide involvement in waterless supercritical carbon dioxide media at 80 °C for only 20 min and without any aqueous after clearing treatment led to approximately 30% and 51% whiteness improvement on cellulosic cotton fiber knitted fabric, respectively. There was no moisture management improvement trend due to caustic soda addition into peroxide bleaching process in waterless scCO2 media. The addition of after-treatment process (catalase enzyme treatment in water at 50 °C and then washed with water at 87 °C in company with wetting agent and rinsing in cold water) following peroxide bleaching in scCO2 media improved the moisture management properties of bleached cotton fabric. Although the bleaching process performed in scCO2 medium resulted in a higher oxidative activity than bleaching process performed in aqueous medium from the measured color yield values of oxycellulose formation evaluation, the consistency of the FTIR (ATR) spectra of the greige, hydrogen peroxide bleached in aqueous and waterless scCO2 media and bleached then after-treated cotton knitted fabrics displays that the respective bleaching process types in both aqueous and waterless scCO2 media had no drastic significant detrimental effect on the surface morphology of the cotton fiber. Consequently, successful waterless hydrogen peroxide bleaching can be carried out for cellulosic cotton fiber knitted fabric in supercritical carbon dioxide media.

Ultrasound-assisted bleaching of canola oil: Improve the bleaching process by central composite design

The goal of this study is to improve the bleaching process of canola oil by using ultrasound treatments under various parameters. The first of these parameters was the temperature (45 °C-75 °C)/ultrasonic power (20%–60%), the second was the amount of bleaching earth (0.1%–2% w/w), and the third was the contact time (2–15 min). The response surface central composite design was created and the bleaching parameters for canola oil were optimized based on the spectrophotometric analysis at 446 nm and responses to the lovibond color scales. The optimum conditions obtained by ultrasonic treatment of canola oil bleaching were compared with the conventional bleaching conditions. Especially, properties of bleached oil such as free fatty acids, peroxides, p-anisidine values, conjugated diens and triens, totox, fatty acid compositions and red-yellow colors have been evaluated. The results showed that integration of the ultrasonic treatment into the bleaching process, could possibly reduce the applied oil temperature by 25%, the contact time by 50%, and the color value by 6–34% compared to the conventional method.

Some Significant Trends in Textile Bleaching

The article highlights some recent trends in the bleaching of textile materials. An attempt has been made to compare the effect of electrochemical bleaching with conventional bleaching of cotton. Electric current is used in the preparation of a bleaching agent to replace bleaching powder. The sodium hypochlorite generated from electrolyte cell is sufficient to produce powerful bleaching agent with available chlorine. Electrochemical bleaching with sodium hypochlorite offers numerous advantages like prevention of effluent problem, economy, reliability, cleanliness, and convenience in working. Attempts have been made to use sodium perborate as a bleaching agent with potassium persulphate as an activator at lower temperature in combined pre treatment of cotton fabric. Experimental trials have been designed by using taguchi technique. This bleaching technique promises to be eco-friendly process. In yet another interesting work, effort has been taken to bleach the scoured cotton fabric with sodium perborate as bleaching agent and tetreacetyl ethylenediamine as bleaching activator. The concentrations of these chemicals, temperature and time of the treatment have been varied. The utilization of hydrogen peroxide is much higher as compared with that of conventional bleaching process. Other advantages include less requirement of water and energy, thereby satisfying needs of eco-friendly process, lesser loss in weight, tearing strength, and tensile strength, in comparison with conventional bleaching process without compromising whiteness index.

Protective Bleaching of Camel Hair in a Neutral Ethanol⁻Water System.

As conventional bleaching under alkaline conditions is chemically damaging to protein fibers, a three-stage protective bleaching process in neutral ethanol–water mixtures was proposed for camel hair using mordanting with ferrous salts, oxidative bleaching with hydrogen peroxide, and reductive bleaching with sodium hydrosulfite. The aim of this work was to improve the whiteness degree of camel hair without substantial tenacity loss. In addition, the roles of ethanol during the bleaching treatment were also examined by characterizing the fibers using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, and X-ray diffraction. The whiteness degree and mechanical properties of camel hair bleached in the neutral ethanol–water system were significantly superior to those of fibers bleached by a conventional method. SEM images showed no visible cracks on the scales of fibers bleached in the ethanol–water system, whereas large grooves were observed on fibers bleached in aqueous solution. TEM images confirmed the positive influence of ethanol on the mordanting process, and FTIR spectra suggested that ethanol reduced the breakage of hydrogen bonds in the fibers during the oxidative bleaching process. These findings indicate the potential of this protective bleaching method for application to a broad range of other natural protein fibers.

Effectiveness of different green chemistry approaches during mixed hardwood bamboo pulp bleaching and their impact on environment

Studies were carried out using conventional bleaching chemicals (chlorine and chlorine dioxide) and green bleaching chemicals (oxygen, enzyme and ozone) to see their effect on the generation of pollutants during bleaching. Results showed that the use of oxygen prior to conventional bleaching reduced the biochemical oxygen demand (BOD), chemical oxygen demand (COD), colour and adsorbable organic halogens (AOX) in the bleaching filtrate by 49–53, 49–56, 70–72 and 48–66, respectively, compared to the use of conventional bleaching chemicals. The use of xylanase enzyme prior to bleaching reduced the colour and AOX in the bleaching filtrate by 5–6 and 9–12% compared to those obtained using conventional bleaching chemicals. The use of oxygen followed by ozone treatment prior to conventional bleaching was able to reduce the BOD, COD, colour and AOX in the bleaching filtrate by 64–68, 73–77, 70–77 and 70–79, respectively, compared to those obtained with the conventional bleaching chemicals. Environmental impact assessment by the index of global pollution methodology suggested that by switching from conventional to green bleaching chemicals the quality of the ecosystem can be improved from class “C” (discomfort to life forms) to class “B” (acceptable to life forms). Application of different green chemistry approaches for the bleaching of mixed hardwood pulp substantially reduced the usage of bleaching chemicals and the generation of pollutants during the bleaching of pulp along with the improvement in quality of the pulp.

Reduction of Chlorophyll in Cold‐Pressed Hemp (Cannabis sativa) Seed Oil by Ultrasonic Bleaching and Enhancement of Oxidative Stability

The effects of ultrasonic bleaching on chlorophyll reduction and oxidative stability of cold‐pressed Cannabis sativa (hemp) seed oil is investigated using three different clays, Sepiolite, activated Bentonite, and an industrial clay. The chlorophyll content is significantly reduced (p &lt; 0.05) from 56.3 μg g−1 in the untreated oil to 14.8 μg kg−1, 9.9 μg kg−1, and 7.8 μg kg−1 in oils treated with Sepiolite, activated Bentonite, and industrial clay, respectively. Oxidative stability is enhanced in all ultrasonically‐treated oils by a significant (p &lt; 0.05) reduction in Peroxide Value (PV) with the highest reduction (97%) observed in the presence of industrial clay (PV = 0.11 mEq kg−1). A corresponding reduction in Conjugated Dienes (CD) is also found in the treated samples ranging from 0.073–0.095% compared to 0.102% for the control. During accelerated storage at 60 °C, increase in PVs and CDs are significantly (p &lt; 0.05) slower for the ultrasonically treated oils in the presence of clays compared to the control. Accelerated storage at 40 °C shows that the PV is greater in hempseed oil bleached with Sepiolite clay compared to a combination of Sepiolite and ultrasonic bleaching. Based on these results it is evident that the rapid removal of chlorophyll from cold pressed hempseed oil is enhanced by a combination of bleaching clay and ultrasonic treatment.Practical Applications: Ultrasonic treatment of cold pressed hempseed oil combined with bleaching clays proves very effective in reducing chlorophyll content. The method is not only rapid and clean but requires significantly less bleaching clay. Hempseed oil treated in this way exhibits greater oxidative stability making it more attractive for industrial and consumer use. The results of ultrasonic bleaching suggest its potential for prolonging the shelf‐life. Utilizing the ultrasonic bleaching technique as an alternative to conventional bleaching would be beneficial to the edible oil industry.The results of ultrasonic bleaching prove effectiveness in reducing chlorophyll content in cold‐pressed hempseed oil and suggest its potential for prolonging the shelf‐life.

Iso-concentration hydrogen peroxide bleaching of poplar chemi-thermomechanical pulp

Maintaining a constant chemical concentration (Iso-concentration, IC) has been found to be an effective method to improve peroxide bleaching efficiency for chemi-thermomechanical pulp (CTMP). In this study, the mechanism of IC bleaching was investigated. The concentrations of H 2 O 2 and total alkali in IC bleaching were monitored and compared with those in conventional bleaching processes. Control experiments without pulp were carried out to explore the effects of bleaching additives on H 2 O 2 decomposition. The results showed that the concentrations of H 2 O 2 and the total alkali at the early and later stages of IC bleaching were relatively low and high, respectively; thus, undesired decomposition of H 2 O 2 was inhibited, and brightness was improved. Moreover, the stabilizer played an important role in inhibiting the undesired H 2 O 2 decomposition. This may explain why high bleaching efficiency was achieved in IC bleaching. These findings would provide valuable insight for the production of high-brightness bleached chemi-thermomechanical pulp (BCTMP).

The Effects of Ozone Bleaching and Ozone Desizing Method on Whiteness and Water Absorption of 100% Cotton Terry Fabrics

In this study, the effects of ozone desizing and bleaching on the hydrophilicity and whiteness of terry fabrics were investigated. The results were compared with those obtained after conventional desizing and bleaching (hydrogen peroxide bleaching). The test samples contain two side piled woven terry cloths of four different areal weights. The ozone desizing and bleaching process was carried out at fixed PH values (6) in four different ozonation times and two different ozone doses. The rate of water pickup in fabrics was 60%. It has been determined that as ozonation time and the ozone dose increase, the degree of whiteness and water absorption of the terry fabric increases. However, the increase in the ozonation time did not cause a significant change in the low ozone doses; the change in the ozonation time at high ozone doses is causing a marked change in the investigated properties of the towel fabric. The degree of hydrophilicity and whiteness achieved after ozonation was found to be close to the results obtained in conventional bleaching. However it was seen that although acceptable water absorbency was obtained by the ozone desizing method, these values were lower than those of the conventional desizing method. Ozone bleaching and desizing do not require the consumption of water, the consumption of heat energy, and the use of any chemical additive that harms the environment with its wastes. As a result, owing to ecofriendly, saving energy and acceptable fabric properties with regard to whiteness and absorptivity, ozone bleaching can be applied instead of the conventional bleaching and desizing method.

Teeth bleaching using diode laser as an adjunct to a bleaching agent

The use of hydrogen peroxide (H2O2) for conventional bleaching was introduced way back in 1884. Today bleaching products are often found in the form of gels containing various concentrations of carbamide peroxide and H2O2depending on the application and methods. Laser-assisted tooth bleaching has proven faster and efficient results. This case report emphasizes on the efficacy of diode laser for tooth bleaching. Opalescent® (Potassium nitrate and fluoride) was used as a bleaching gel. Diode laser (810 nm) was used to irradiate the tooth surfaces and microabrasion was carried out. Visible reduction in tooth discoloration was seen after a period of 3 weeks. On the basis of the results obtained, diode laser can be considered as an efficient and reliable treatment modality compared to conventional bleaching.

Ultrasound-assisted bleaching of olive oil: Kinetics, isotherms and thermodynamics

Experimental data of the adsorption of carotenoids and chlorophylls were investigated to obtain adsorption kinetic, isotherm and thermodynamic information during ultrasound-assisted bleaching (US bleaching) of olive oil and to compare them with the results from conventional bleaching method. Adsorption of pigments on activated bentonite was rather fast and efficient by applying ultrasound. In both bleaching procedures, the kinetics of carotenoids adsorption followed pseudo-first order model whereas pseudo-second order equation gave a better fit to the adsorption of chlorophylls. It is speculated that adsorption of carotenoids is mainly facilitated by physisorption while chemical reactions are also involved in the removal of chlorophyll pigments under sonication. Equilibrium study shows that the adsorption behavior of the two pigments is different. Freundlich isotherm provided accurate estimates of adsorption equilibrium data of chlorophylls during US bleaching indicating a multilayer adsorption under ultrasound irradiation. According to the thermodynamic analysis, both bleaching methods are endothermic and spontaneous with increased randomness at the solid-liquid interface.

Absorption spectra of gelatin copper complexes and copper (II) sulfate and their impact on cotton peroxide bleaching

ABSTRACTA gelatin copper complex was synthesized with gelatin and copper (II) sulphate. The previous study had indicated that the gelatin copper complex could improve peroxide bleaching effectiveness of cotton in low-temperature. By measuring the spectra absorption abilities of gelatin, copper (II) sulphate and gelatin copper complex respectively, it proved that gelatin copper complex was formed. The catalytic bleaching effectiveness of H2O2/gelatin copper complex system and H2O2/copper (II) sulphate system were compared. The results show that the gelatin copper complex and copper (II) sulphate can catalyze hydrogen peroxide decomposition and improve the whiteness of bleached cotton. Whiteness and capillary effects of the cotton fabric bleached in H2O2/gelatin copper complex system and in H2O2/copper (II) sulphate system at 70℃ are close to the conventional high-temperature bleaching. Besides, the strength retention of the fabric bleached in H2O2/gelatin copper complex system at 70℃ is the biggest among the three samples. The strength retention of the fabric bleached in H2O2/copper (II) sulphate system at 70℃ is the smallest among the three samples. So gelatin copper complex is a more effective catalyst than copper (II) sulphate in low temperature peroxide bleaching of cotton fabric.

Comparison of Tooth Color Change After Bleaching With Conventional and Different Light-Activated Methods.

Introduction: The demand for esthetic dental treatments is increasing in recent years mainly due to improved oral hygiene and better maintenance of oral health and teeth in older individuals. Bleaching of discolored anterior teeth is the most popular among esthetic dental treatments. Even individuals with sound teeth and adequate esthetics seek to have whiter teeth in the anterior region. The aim of this study was to evaluate tooth color changes following conventional in-office bleaching techniques compared to light-activated methods using different light sources. Methods: Seventy sound anterior teeth (devoided of caries and/or fracture), extracted for periodontal and orthodontic reasons were selected and allocated to 7 groups: (A) control, (B) conventional bleaching (C) LED-activated bleaching, (D) KTP laser-activated bleaching, (E) diode laser-activated bleaching, (F) Nd:YAG laser-activated bleaching and (G) CO2 laser-activated bleaching. Colorimetric evaluation was carried out before and after treatment using a spectrophotoradiometer. Data were analyzed by one- and two-way analysis of variance (ANOVA) as well as multiple comparison methods. Results: The results showed that all bleaching procedures were effective in reducing the yellowness index. However, the KTP laser-activated bleaching was significantly more effective than the other techniques in 95% confidence level. It was also seen that CO2 laser activated method has outperformed groups E, F and G and the conventional bleaching without light activation was not effective at all and represented similar results with the control group. Furthermore, the groups E and G had almost the same results in decreasing the yellowness index. Conclusion: The results showed that all bleaching techniques were effective however, the KTP laser-activated bleaching was significantly more efficient, closely followed by the CO2 laser-activated bleaching technique.

In Vitro Effect of Bleaching With 810 nm and 980 nm Diode Laser on Microhardness of Self-cure and Light-Cure Glass Ionomer Cements.

Introduction: This study sought to assess the effect of bleaching combined with irradiation of 810 nm and 980 nm diode laser on microhardness of 2 commonly used self-cure and light-cure glass ionomer cements (GICs) in comparison with conventional bleaching (without laser). Methods: In this in vitro, experimental study, 60 samples were fabricated of A2 shade of Fuji IX and Fuji II LC GICs (n=30) and each group was divided into 3 subgroups (n=10). The first subgroups were subjected to bleaching with Opalescence Xtra Boost plus 980 nm diode laser irradiation. The second subgroups were subjected to bleaching with Opalescence Boost plus 810 nm diode laser irradiation and the third subgroups were subjected to bleaching with Opalescence Xtra Boost without laser. Microhardness was measured at baseline and after the intervention using Vickers hardness tester. The data were analyzed using two-way analysis of variance (ANOVA) (P<0.05). Results: Microhardness decreased in all subgroups after the intervention (P<0.001) irrespective of the type of GIC (P=0.201) or surface treatment (P=0.570). The baseline microhardness of the three subgroups within each group of GIC was not significantly different (P=0.456), but the baseline microhardness of conventional GIC was significantly higher than that of resin modified GIC (P=0.004). Conclusion: Bleaching with/without laser irradiation decreases the microhardness of GICs. The baseline microhardness of conventional GIC is higher than that of resin modified GIC.

Establishment of an effective activated peroxide system for low-temperature cotton bleaching using synthesized tetramido macrocyclic iron complex

In this study, the tetramido macrocyclic iron complex (Fe-TAML) was successfully synthesized, and then it was characterized using 1H nuclear magnetic resonance (1H NMR), electrospray ionization mass spectrometry (EIS-MS) and elemental analysis. An activated peroxide system was established for low-temperature bleaching of cotton by combining the synthesized catalyst (Fe-TAML) with hydrogen peroxide. Experimental results showed that the Fe-TAML/H2O2 bleaching system exhibited effective bleaching performance in the use of 2 μM Fe-TAML, 20 g/l H2O2, 1 g/l NaHCO3, 2 g/l scouring agent and 2 g/l wetting agent at 60 °C for 60 min. In comparison with the conventional bleaching system, the Fe-TAML/H2O2 system provided bleached cotton with a superior degree of whiteness, higher tensile strength and acceptable water absorbency. The application of Fe-TAML was expanded and the activated peroxide system may provide a green approach for the cotton bleaching.

Evaluation of the Effect of Different Laser Activated Bleaching Methods on Enamel Susceptibility to Caries; An In Vitro Mode.

Introduction: Today, bleaching is a routine noninvasive alternative for treatment of discolored teeth. The aim of this study was to determine whether conventional or laser activated bleaching predispose teeth to develop caries or not. Methods: Sixty human molars were mounted on acrylic cylinders and their Knoop microhardness (KHN) as well as DIAGNOdent (DD) values were recorded. They were divided into 4 experimental groups; G1) conventional bleaching with 40% hydrogen peroxide gel, G2) Diode laser assisted bleaching with same gel, G3) Nd:YAG laser assisted bleaching with the same gel, G4) control group. After bleaching, all samples were subjected to a three day pH cycling regimen and then, KHN and DD values were measured. Results: All groups had significant reduction in KHN values. It seems that there is no statistically meaningful difference between changes in enamel microhardness of the sample groups and all groups have changed in a similar amount. Reduction of DD scores were significant in Diode laser and conventional groups, however changes in Nd:YAG laser and control groups were not significant. Changes in DD values have followed a similar pattern among groups, except in G1- G4 and G2-G4 couples. Conventional and diode laser groups had a meaningful difference in reduction of DD values in comparison with the control group. Conclusion: It can be concluded that bleaching whether conventional or laser activated, does not make teeth vulnerable to develop carious lesions.

Spectrophotometric analysis of the effectiveness of a novel in-office laser-assisted tooth bleaching method using Er,Cr:YSGG laser.

The purpose of this in vitro study was to compare the effectiveness of a novel Er,Cr:YSGG laser-assisted in-office tooth bleaching method with a conventional method by spectrophotometric analysis of the tooth color change. Furthermore, the influence of the application time of the bleaching gel on the effectiveness of the methods and the maintenance of the results 7days and 1month after the treatments were also evaluated. Twenty-four bovine incisors were stained and randomly distributed into four groups. Group 1 specimens received an in-office bleaching treatment with 35% H2O2 for 2×15min. Group 2 specimens received the same treatment but with extended application time (2×20min). In Group 3, the same in-office bleaching procedure (2×15min) was carried out as that in Group 1, using Er,Cr:YSGG laser irradiation for 2×15s on each specimen to catalyze the reaction of H2O2 breakdown. Group 4 specimens received the same bleaching treatment as Group 3 but with extended application time (2×20min). Er,Cr:YSGG laser-assisted tooth bleaching treatment is more effective than the conventional treatment regarding color change of the teeth. Application time of the bleaching agent may influence the effectiveness of the methods. The color change of the tested treatments decreases after 7days and 1month. The clinical relevance of this study is that this novel laser-assisted bleaching treatment may be more advantageous in color change and application time compared to the conventional bleaching treatment.

Biobleaching of banana fibre pulp with incorporation of xylanase enzyme fromAspergillus oryzae

The potential of extracellular xylanase produced by Aspergillus oryzae through solid state fermentation was investigated on banana fibre pulp bleaching in association with conventional bleaching with chlorine dioxide. The maximum enzyme production was obtained at 30 o C after 48 hrs of incubation using wheat bran substrate. Highest enzyme activity 1136 IU/g dry substrate was found under optimized condition. Banana fibre pulp were pretreated with different dose of xylanase enzyme before the conventional bleaching sequence. Xylanase pre-treatment reduce the kappa no and enhance the optical and physical properties of pulp. The maximum reduction in kappa no were 1.3 unit at the dose of 30 IU/g. Xylanase treatment also improve burst index, tensile index and double fold by11.81 per cent, 5.7 pera cent and 2.8 per cent, respectively.

Comparative study of intrapulpal temperature stress during Er,Cr:YSGG-supported dental bleaching versus conventional dental power bleaching. An in vitro study

The purpose of this in vitro study was to evaluate the safety of the Er,Cr:YSGG bleaching treatment in terms of pulp chamber temperature increase in teeth, as well as to test two different bleaching gels applied in the same procedure. Our previously published pilot study suggested that the most susceptible teeth during Er,Cr:YSGG-supported bleaching are the maxillary lateral incisors and mandibular incisors. These two types of teeth were used in order to assess the safety of the procedure with regard to tooth vitality. For the needs of this study, 60 teeth were tested (30 maxillary lateral incisors (TT1) and 30 mandibular incisors (TT2)). The experimental procedure involved the use of an Er,Cr:YSGG laser (2780 nm, Waterlase MD, Biolase, USA) with two different bleaching gels. A yellow-colored bleaching agent, with a concentration of 38% H2O2 (Power whitening, WHITEsmile GmbH, Germany) (BG 1), and a purple-colored agent for in-office tooth whitening, with a concentration of 35% H2O2 (Laser-White20, Biolase) (BG 2), were utilized in the experiment. The tip employed was a 6-mm-long Z-type glass tip (MZ8) of 800 μm diameter. As to the applied power settings, the average output power was set at 1.25 W and the pulse duration at 700 μs (S-mode), while the pulse repetition rate was 10 Hz. The results showed that during Er,Cr:YSGG-supported tooth bleaching, the temperature rise in the pulp chamber did not exceed the temperature threshold of 5.6 °C, regardless of the bleaching gel used (2.03 ± 0.55 °C for BG1 and 1.53 ± 0.48 °C for BG2) and can therefore be considered a safe procedure. Moreover, a time-consistent higher temperature difference was observable during the BG1 application, compared to that of BG2.

Refinement of industrial kaolin by removal of iron-bearing impurities using thiourea dioxide under mechanical activation

This study reports a series of experiments conducted to evaluate the suitability of thiourea dioxide (TD) under mechanical activation, in bleaching iron-bearing impurities from raw kaolin. The optimum conditions for the maximum whiteness of 76.32% were determined as follows: rotation speed of ball mill, 400rpm; activation time, 1.5h; TD dosage, 0.8% of kaolin mass; solid-to-liquid ratio, 1:2; pH, 8.0; room temperature. The effect of grinding causes the partial surface amorphization of kaolin particles and a decrease in the dehydroxylation temperature. The assistance of grinding leads to a higher iron removal when compared with the conventional bleaching method using sodium hydrosulfite.