Peroxide Bleaching Research Articles

Quantitative analysis of the degree of demineralization for bleached enamel by optical coherence tomography

BackgroundTooth bleaching imparts whitening effects along with adverse effects such as increased tooth sensitivity and enamel surface changes. Herein, we employed optical coherence tomography (OCT), a nondestructive optical detection technique, for evaluation of tooth enamel after treatment with peroxide-based bleaching agents. MethodsFifteen enamel samples were bleached using 38% acidic hydrogen peroxide-based bleach, subjected to OCT scanning, and then cross-sectioned and imaged under polarized light microscopy (PLM) and transverse microradiography (TMR). OCT cross-sectional images were compared with PLM and TMR. The depth and severity of demineralization produced in the bleached enamel were measured by OCT, PLM, and TMR. Comparison between the three techniques was performed using Kruskal-Wallis H non-parametric test and Pearson correlation. ResultsIn comparison with PLM and TMR, OCT clearly detected the changes in the enamel surface after hydrogen peroxide bleaching. Significant correlations (p<0.05) were observed in lesion depth between OCT and PLM (r=0.820), OCT and TMR (r=0.822), and TMR and PLM (r=0.861). There was no statistically significant difference in demineralization depth values measured by OCT, PLM, and TMR (p>0.05). ConclusionOCT can allow real-time, non-invasive imaging of artificially bleached tooth models and automatically measure the early changes in the enamel lesion structure upon exposure to hydrogen peroxide-based bleaching agents.

Influence of violet LED and fluoride-containing carbamide peroxide bleaching gels on early-stage eroded/abraded teeth

PurposeThis study evaluated enamel with early-stage erosion/abrasion following bleaching with 20% and 45% carbamide peroxide (CP) gels containing fluoride (F) and irradiated with violet LED (LED). MethodsEnamel blocks were immersed in 1% citric acid (5 min) and artificial saliva (120 min) three times to produce early-stage enamel erosion. Simulated toothbrushing was performed only after the first saliva immersion, to provoke enamel abrasion. The erosive/abraded enamel samples were submitted to (n=10): LED/CP20, CP20, LED/CP20_F, CP20_F, LED/CP45, CP45, LED/CP45_F, CP45_F, LED, and control (without treatment). The pH of the gels was assessed, and color (ΔE00) and whiteness index (ΔWID) changes were calculated after cycling (T1), and 7 days from bleaching (T2). Enamel surface roughness average (Ra) and Knoop microhardness (kg/mm2, %SHR) were evaluated at baseline (T0) at T1 and T2. Scanning electron microscopy evaluated the enamel surface morphology at T2. ResultsThe gels’ pH was neutral and CP20 and CP45 exhibited no differences in ΔE00 and ΔWID (p>0.05) but LED increased these parameters for CP20_F and CP45. Erosion/abrasion significantly decreased mean kg/mm2, and the LED group was the only one not increasing microhardness after bleaching (p>0.05). None of the groups fully recovered the initial microhardness. All groups exhibited %SHR similar to the control (p>0.05) and the increase in Ra was detected only after erosion/abrasion. CP20_F groups exhibited a more preserved enamel morphology. ConclusionLight irradiation combined with low-concentrated CP gel promoted a bleaching effect comparable to the high-concentrated CP. The bleaching protocols did not adversely impact the surface of early-stage eroded/abraded enamel.

Can antioxidant treatment replace delay in bracket bonding? An in vitro study

BackgroundDeterioration in shear bond strength has been reported after immediate bracket bonding following hydrogen peroxide bleaching. This study compared the effectiveness of three antioxidant agents, namely, alpha-tocopherol, green tea extract, and sodium ascorbate, in reversing the bleaching effect and as possible alternatives to delayed bonding.MethodsA total of 105 extracted human premolars were arbitrarily assigned to 7 groups (n = 15 each), including group 1 as the unbleached control group and six experimental groups, which were bleached with 40% hydrogen peroxide in three sessions of 15 min each. In experimental group 2, bonding was performed immediately after bleaching, whereas in groups 3 and 4, bonding was delayed for 1 and 2 weeks, respectively; meanwhile, the specimens were immersed in artificial saliva at 37 °C. Groups 5, 6, and 7 were treated immediately after bleaching with 10% of alpha-tocopherol, green tea extract, and sodium ascorbate solutions, respectively, for 15 min. Specimens were processed using 500 thermal cycles between 5 and 55 °C, with a dwell time of 30 s after 24 h of bracket bonding, and then tested for shear bond strength. The adhesive remnant index was examined to evaluate fracture mode. One-way analysis of variance, Kruskal–Wallis H, and post hoc Tukey’s honestly significant difference tests were used to compare the data. Significant results were subjected to pairwise comparisons with Bonferroni’s correction-adjusted of p values ≤ 0.050.ResultsShear bond strength was significantly lower (p < 0.001) in the immediate bonding and 1-week delay groups than in the control group. However, no significant difference was detected among the 2-week delay, antioxidant-treated, and control groups (p > 0.05).ConclusionsApplication of 10% alpha-tocopherol, green tea extract, or sodium ascorbate for 15 min could restore shear bond strength after 40% hydrogen peroxide bleaching as an alternative to delay in bracket bonding.

Evaluating chelating agents and their effects on cellulosic pulps during P-stage bleaching. Part 1: analytical method development

During peroxide bleaching of pulp (“P-stage”), the heavy metal ions must be removed from the pulp and inactivated by chelation before the bleaching to prevent undesired degradation of cellulose by reactive oxygen species. Ethylenediaminetetraacetic acid (EDTA) is mostly used as a chelating agent; however, it may soon be banned because of environmental concerns. Therefore, there is a demand for new chelating agents to replace EDTA, and a comprehensive analytical method is necessary to investigate their chelating ability and the effects on the pulp. In this study, an analytical sequence for evaluating chelating agents and oxidative damage to cellulose during chelation (Q-stage) and bleaching (P-stage) has been established and optimized. GPC provides the molar mass distribution and oxidative damage (as profiles of carbonyl groups relative to the molar mass distribution), and the metal content of the pulp was determined by ICP-OES. This method enables the analysis of the chelating potential of new chelating agents, with simultaneous determination of the impact on cellulose on a molecular level.Graphical abstract

Physicochemical evaluation of hydrogen peroxide bleaching gels containing titanium dioxide catalytic agent, and their influence on dental color change associated with violet LED.

The purpose of this study was: 1) to analyze the physical-chemical properties of hydrogen peroxide (HP) agents at 7.5% (HP7) and 35% (HP35), and the association with or without TiO2 nanotubes; 2) to evaluate dental bleaching effectiveness by using HP7 and HP35 together with or without TiO2 nanotubes, and applied with or without violet LED (VL). 80 bovine incisors were treated according to groups (n=10): HP35; HP35+VL; HP35T (HP35+TiO2); HP35T+VL; HP7; HP7+VL; HP7T (HP7+TiO2); HP7T+VL. Bleaching effectiveness was measured at 4 time points according to the Vita Classical, CIEL*a*b*, CIEDE2000, and WID parameters. HP35, HP35T, HP7, and HP7T were evaluated for mass change, pH, mean particle size (P), polydispersity (PDI), and zeta potential (ZP), over 6 months of storage. The pH of HP35 thickener was higher when associated to TiO2. At baseline, both of the bleaching gels containing TiO2 had lower P, PDI, and PZ (p<0.05). All groups showed a significant decrease in Vita Classical color scores (p=0.0037). There was a higher L* value, and lower b* values for HP7 when associated to VL after the 3rd session. (p<0.05). HP35T showed higher color change (ΔEab, ΔE00), and lower a* value in the presence of VL (p<0.05). ΔWID presented lower values for both gels, when TiO2 was incorporated (p≤0.05). The incorporation of TiO2 to the bleaching gel showed good stability with minimal variations in physical-chemical properties. The color change in HP35 was more effective than in HP7, but the VL boosted the bleaching effectiveness of HP7, whereas TiO2 did not increase bleaching effectiveness.

Enhanced bleachability of chemi-thermomechanical pulp by hydrogen peroxide bleaching in ethanol-water media

Hydrogen peroxide (H2O2) bleaching in ethanol-water media was used to improve the bleaching efficiency of the chemi-thermomechanical pulp (CTMP). The brightness of CTMP increased and the yellowness decreased when the ethanol ratio was increased to 50%. However, when more than 50% ethanol was added, the brightness decreased, and the yellowness increased. In general, H2O2 bleaching in ethanol-water media, except for 100% ethanol, improved the optical properties of CTMP compared to conventional H2O2 bleaching. Moreover, the chemical composition of CTMP did not alter significantly. The best bleaching condition for CTMP was observed in 50% ethanol at a bleaching temperature and time of 80 °C and 120 min, respectively. The brightness of CTMP under this condition increased by approximately 22% compared with conventional H2O2 bleached CTMP. Principal component analysis (PCA) revealed that the optical properties of bleached CTMP were affected by the structural changes of the aromatic ring and carbonyl group in lignin and carbonyl group in hemicellulose. Consequently, the specific optimal ratio of ethanol that could improve the optical properties of CTMP was determined. The results can serve as a reference for fabricating improved CTMP for its practical application in high-grade papermaking.

Hierarchically Designed Biodegradable Polylactide Particles with Unprecedented Piezocatalytic Activity and Biosafety for Tooth Whitening.

At-home tooth whitening solutions with good efficacy and biosafety are highly desirable to meet the ever-growing demand for aesthetic dentistry. As a promising alternative to the classic peroxide bleaching that may damage tooth enamel and gums, piezocatalysis has been recently proposed to realize non-destructive whitening by toothbrushing with piezoelectrical particles. However, traditional particles either pose potential threats to human health or exhibit low piezoresponse to weak mechanical stimuli in the toothbrushing. Here, biocompatible and biodegradable polylactide particles constructed from interlocking crystalline lamellae have been hierarchically designed as next-generation whitening materials with ultra-high piezocatalytic activity and biosafety. By simultaneously controlling the chain conformation within lamellae and the porosity of such unique lamellae network at the nano- and microscales, the particles possessing unprecedented piezoelectricity have been successfully prepared due to the markedly increased dipole alignment, mechanical deformability, and specific surface area. The piezoelectric output can reach as high as 18.8 V, nearly 50 times higher than that of common solid polylactide particles. Consequently, their piezocatalytic effect can be readily activated by a toothbrush to rapidly clean the teeth stained with black tea and coffee, without causing detectable enamel damage. Furthermore, these particles have no cytotoxicity. This work presents a paradigm for achieving high piezoelectric activity in polylactide, which enables its practical application in tooth whitening.

Efficacy and safety of carbamide peroxide tooth-whitening gels

Carbamide and hydrogen peroxide are the most frequently utilized compounds for various whitening techniques, that differ as per peroxide level, method of administration, and exposure period, when it comes to the active solutions accessible for important tooth whitening. The 10±1% carbamide peroxide dosage was the only level to date to acquire the American Dental Association's stamp of approval, ensuring its safety and effectiveness for at-home tooth whitening with customized trays. There has been a noticeable growth in the range of in-office tooth whitening compounds commercially available, which typically use elevated carbamide peroxide levels (30 to 37%) with or without an additional illumination. Even though tooth sensitivity appears to be the most frequent side effect of carbamide peroxide bleaching, discomfort goes away when the plan of care is finished. Sensitivity is typically linked to a background of sensitive teeth, greater administration rate, or use of greater carbamide peroxide levels. Additionally, studies have showed that using 10% carbamide peroxide at home to lighten teeth had comparable effectiveness to other methods (over the counter or in-office whitening). Patients generally prefer home vital bleaching with 10% carbamide peroxide to office procedures with 35% hydrogen peroxide. When comparing the safety utilizing 16% carbamide peroxide for nightguard vital bleaching to a placebo or 10% carbamide peroxide, patients receiving 16% reported higher gingival soreness than those administered a 10% carbamide peroxide or a placebo.

Bleaching effectiveness and cytotoxicity of new experimental formulation of niobium-based bleaching gel.

The development of new bleaching agents with minimum concentration of hydrogen peroxide (HP), without adverse effects, and with bleaching effectiveness, has great clinical relevance. The aim of this study was to evaluate the bleaching efficacy and cytotoxicity of a new niobium-based bleaching gel, compared to already available HP-based gels. For the bleaching efficacy analysis, 40 bovine incisors were randomly divided into 4 groups according to the established bleaching protocol: control, untreated; 35HP, 35% HP bleaching gel; 6HP, 6% HP bleaching gel; NbHP, niobium gel associated with 3% HP gel. The color variation was measured in a spectrophotometer and the values of ΔL, Δa, Δb, and ΔE obtained. For the cell viability assay by MTT, MC3T3 cells were exposed to bleaching gel extracts (1:500, 1:250, 1:125 dilutions; immediately and 24h). Statistical tests were performed (P < 0.05). The color alteration for all bleaching gels was significant compared to control (P < 0.05), but the NbHP gel showed a significant ΔE than other gels, with expressive color alteration at 14days (P < 0.05). The 35HP showed high cytotoxicity regarding control and the most groups in all periods and extracts analyzed (P < 0.05), while the NbHP showed greater cell viability than control in the immediate period, dilution of the 1:500 and superior to 6HP in the most extracts at 24h. The new experimental niobium-based gel has bleaching efficacy similar to that of gels with a high concentration of HP, and it has high cytocompatibility. The use of this new generation of niobium-based whitening gel associated with a low concentration of hydrogen peroxide represents the possibility of a tooth whitening with lower dentin sensitivity.

Bamboo cellulose based single cell protein and nanocellulose by dilute sulfuric acid hydrolysis and fermentation

The novel and facile multi-stage method was used for the conversion of bamboo into nanocellulose and single cell protein. Firstly, the bamboo chips were treated with sodium hydroxide solution followed by hydrogen peroxide bleaching for obtaining cellulose pulp with a brightness of 80% ISO. In the second stage, the obtained bleached cellulosic pulp was achieved with a dilute sulfuric acid and hydrogen peroxide followed by filtration for obtaining the sugar solution, which than was treated and used for Candida utilis cultivation, and nanocellulose, which than was submerged purification and refining for obtaining nanocellulose fibers. The optimal conditions of the yeast cultivation were dertermined for obtaining the single cell protein with protein content of approx. 49.5 wt.%. For isolation of nanocellulose with fiber diameter &lt; 100 nm were proposed: concentration of hydrogen peroxide 0.25 wt.%, the concentration of sulfuric acid 0.75 wt. %, liquor to cellulose ratio 8 to 1, temperature 140oC, time 120 min. The characteristics of nanocellulose were studied by SEM, FTIR, and XRD.

Arabica Coffee Pulp Cellulose: Isolation, Morphology, and its Capabilities to be Modified into Cellulose Nitrate

Cellulose nitrate was a cellulose derivative applied in various applications, from plastics to solid propellants for military ammunition and rocketry. Environmental impact from using cotton linter or wood as a source of cellulose for cellulose nitrate industry promoting attempt to use agricultural waste as an alternative source of cellulose. Utilizing non-wood agricultural waste is also advantageous to reduce waste accumulation and give economical value. However, specific cellulose properties should also considered to achieve optimum cellulose derivation process into cellulose nitrate through nitration reaction. Coffee pulp waste had potential to be used as source of non-wood cellulose for its abundance, considerable fraction of cellulose content, low economical value, and unique cellulose morphology. In this study, the cellulose from the coffee pulp was isolated through sodium hydroxide and hydrogen peroxide bleaching method, which furthermore evaluated in terms of their morphology, physical properties, and its capabilities to be derived into cellulose nitrate. The result showed that coffee pulp cellulose has crystallinity and surface area around 59.63% and 0.5962 m2/g, respectively which is lower than cotton linter, suggesting advantageous properties for nitration reaction. Nitration to coffee pulp-based cellulose resulted in moderate nitrogen content cellulose nitrate which still suitable for non-military application.

Investigating cotton dyeing using exotic wood waste sawdust

Investigating cotton dyeing using exotic wood sawdust. The study investigated the possibility of using extracts from various species of exotic wood, obtained from waste sawdust, for dyeing cotton fabrics. Material from Obeche, Iroko, Merbau, Apple tree, American walnut, Tulip tree, Cumaru and Rosewood were used for the tests. Solutions of oxalic acid, tin chloride, aluminum sulfate and ferric chloride were used as mordants, along with no-mordant tests. The color was determined in the CIE L*a*b* coordinate system. Color fastness was tested using n-hexane for dry cleaning and acidic, alkaline and hydrogen peroxide bleach solutions. The results showed a strong dependence on the type of wood, the mortar used and the washing agent and covered a wide spectrum of color intensity and fastness. The best results were obtained for Rosewood, Merbau and Apple trees, while Tulip tree and American walnut turned out to be practically useless. Among the mordants used, the most intense colors were produced by metal salts, including ferric chloride, which strongly darkened fabrics. Dry cleaning proved to be the mildest of those tested, with the least effect on color fading.

Effect of highly concentrated bleaching gels on enamel microhardness and superficial morphology, and the recovery action of four remineralizing agents

BackgroundDental bleaching is a common clinical practice. The aim of this study is to investigate the effect of 35% hydrogen peroxide (HP) bleaching gel on the morphology and microhardness of enamel, and to analyze the effect of four remineralizing agents.MethodsOne hundred blocks were prepared. The enamel surfaces were bleached with 35% HP in one session. The specimens were divided into four remineralization treatment groups (n = 25). G1: Tooth Mousse, G2: Remin-Pro, G3: Colgate Pro-Relif, G4: Mirafluor. The remineralizing protocol was applied 3 min per day for one week. Vickers microhardness (HV) measurements and SEM observations were performed at baseline, after bleaching, and after remineralizing treatment in all groups. Statistical analyses were performed using the paired t-test and ANOVA.ResultsAfter bleaching, SEM showed an increase of irregularities on the surface of the samples. Enamel microhardness decreased a mean of 47.7 HV, equivalent to a mean decrease of 18.3% (p < 0.05). After remineralization, the HV increased in all groups between 16 and 33% (p < 0.01), recovering the initial microhardness of enamel samples. SEM images revealed a higher quantity of superficial mineral deposits in groups 1 and 2 compared to the rest of the groups.ConclusionsThe application of remineralizing products generates a significant increase in enamel microhardness. Tooth Mousse-treated samples showed a greater microhardness recovery, followed by Remin Pro. The superficial morphology of the samples reflects the results obtained in the HV tests.

Bleaching intracoronal gigi insisif pertama pasca perawatan endodontik (Laporan Kasus)

Background: Non-vital anterior tooth discoloration is a common concern in everyday clinics. Increased patient demand for affordable and excellent results makes bleaching treatment for discolored teeth one of the most popular treatment options. Bleaching offers a more conservative and aesthetic solution compared to treatments like dental crown. Objective: To restore the color of the upper right maxillary incisor after endodontic treatment using internal bleaching with 35% hydrogen peroxide. Case: A 22-year-old male patient came with a complaint of discoloration of upper right maxillary incisor. On clinical examination, upper right maxillary incisor was discolored. On radiographic examination, radiolucency was observed in the periapex. Endodontic treatment was performed with biomechanical preparation using circumferential filing technique and obturation of root canals using a thermoplastic injection technique. At the next visit, an intraoral photo was taken, and the color upper right maxillary incisor was determined using a shade guide. Intracoronal bleaching was performed using 35% hydrogen peroxide bleaching gel. After the color of upper right maxillary incisor has blend well, then the teeth were restored using a composite resin. Conclusion: Intracoronal bleaching treatment with 35% hydrogen peroxide is a conservative and aesthetic treatment to restore the color of the tooth with an excellent result.

Optimization of Cellulose Extraction and TCF Bleaching from Olive Tree Pruning Residues by Box–Behnken Design

ABSTRACT In this work, we successfully produced Totally Chlorine Free (TCF) Bleached pulp from olive tree pruning residues using the soda-anthraquinone pulping method. TCF pulp bleaching was carried out using a chelating–hydrogen peroxide bleaching sequence. Box–Behnken design (BBD), as an experimental design for response surface methodology (RSM), was used to study the effects of the different operating conditions on the cellulose extraction and bleaching pulp and to find an optimum for each process. After pulping under optimum conditions, we obtain a yield of 28.84% for leaves and 44.18% for stems, with a kappa number of 19.74 for leaves and 36.87 for stems. Soda-anthraquinone pulps from olive tree pruning residues were then bleached with a TCF sequence, reaching a value of brightness of about 82 and a kappa number of 10.13 for leaves and 13.69 for stems. A morphological study was investigated using scanning electron microscopy (SEM), showing the raw material structures and the fiber surfaces after delignification and bleaching processes. Isolated cellulose under optimum conditions was characterized using Fourier transform infrared spectroscopy (FTIR) confirmed that cellulose amolecules were not removed using several chemical treatments both of delignification and bleaching stages.

Allomorphic regulation of bamboo cellulose by mild alkaline peroxide for holocellulose nanofibrils production

The exploration of sustainable lignocellulosic nanomaterials with unique properties and applicable functions is receiving growing interest. In this work, holocellulose nanofibrils (HCNFs) were prepared from moso bamboo using mild alkaline peroxide bleaching method (MAPB) followed by mechanical nanofibrillation. MAPB was proved to effectively remove lignin and retain hemicellulose. Meanwhile, partial allomorphic changes from cellulose I to cellulose II were revealed together with varying degrees of crystallinity. Thermogravimetric analysis (TGA) experiment showed an increasing thermal stability trend due to more allomorphic changes into anti-parallel cellulose II. Well-dispersed HCNFs suspensions were successfully prepared by homogenization and HCNFs films with high transparency and flexibility were fabricated. The films reached the maximum tensile strength of 55.8 MPa and tensile strain of 1.55 % along with a calculated toughness of 25 MJ/m3. Moreover, the prepared materials are biocompatible and completely non-toxic, which will theoretically support the application of HCNFs materials in fields of biology, medicine and food industry.

Chemical behavior of 20%-22% carbamide peroxide gels in at-home bleaching: Randomized crossover in situ trial.

To evaluate if distinct 20%-22% carbamide peroxide bleaching gels present similar decomposition pattern and pH during the clinical use in both arches, as well as gels viscosity. Participants randomly received treatments with carbamide peroxide gels (n=10): OPF (OpalescencePF-20%); PNT (Polanight-22%); and WPC (Whiteness Perfect-22%) in three different days, with 2-day washout. Decomposition pattern was assessed by peroxide concentration. Both PC and pH of bleaching gels were measured in different time points in upper and lower trays during a total of 120 min of clinical use. Viscosity of bleaching gels was measured in triplicate. ANOVA and Tukey's test were applied (α=0.05). Regarding decomposition pattern, no significant differences were observed for the interaction between gel, time, and tray position factors. The peroxide concentration progressively reduced until 120 min of trays use (p < 0.001), being overall more notable in lower trays (p < 0.001). Regarding pH, the lowest values were verified in WPC within time. At 120 min, an increase of pH was observed for both WPC and OPF (p < 0.001) compared to baseline means. PNT exhibited constant pH values over time. The values of viscosity were: OPF (1.682.000 ± 19 cP)a, WPC (1.388.667 ± 172.63 cP)ab, PNT (579.567 ± 0.98 cP)b. The bleaching gels presented overall decomposition pattern clinically equivalent, being more notable in lower trays over time. Nevertheless, distinct pH and viscosities were observed among the products. Although the manufacturers recommend different times of use for bleaching gels with similar peroxide concentrations, the commercial products tested did not exhibit clinically relevant difference in the decomposition pattern during the 120 min of clinical procedure.

DEVELOPMENT TECHNOLOGY OF SULFITE PULP TCF BLEACHING FOR CHEMICAL PROCESSING

An environmentally friendly chlorine-free technology for producing wood sulfite soluble pulp using only one oxidizing bleaching agent – hydrogen peroxide has been developed: unconventional catalyzed peroxide delignification and hydrogen peroxide bleaching. The conditions of cooking, delignification, extraction and bleaching of spruce sulfite pulp obtained as a result of studies, as well as successful combinations of conditions of all stages made it possible to obtain two types of soluble pulp by one technology: soluble pulp for nitration (for gunpowder) was obtained under a short scheme including a delignification step and hot alkaline extraction; by continuing this scheme with hydrogen peroxide bleaching in two steps, viscose pulp was obtained. The use of this technology will make it possible to implement a double import substitution – in raw materials (wood instead of cotton) and in finished products (pulp for chemical processing - for nitration and viscose pulp, which are currently imported).

The impact of bleaching on the yield of softwood kraft pulps obtained by high alkali impregnation

AbstractHigh alkali impregnation (HAI) increases the total yield of softwood pulps following kraft cooking. This yield improvement is also maintained after oxygen delignification. This study evaluates how bleaching with either chlorine dioxide or hydrogen peroxide affects the final yield of samples obtained with standard and HAI. The chemical composition, viscosity, brightness, mechanical and morphological properties were studied. Compared to cooking after standard impregnation the yield improvement achieved by HAI was preserved in both types of bleaching sequences (2 % units for chlorine dioxide and 4 % units for hydrogen peroxide). The introduction of charged groups into the cellulose fibers was higher with hydrogen peroxide bleaching than with chlorine dioxide however, no significant impact was seen on the swelling or mechanical properties. The brightness was higher for the pulps bleached with chlorine dioxide compared with hydrogen peroxide. Hydrogen peroxide bleaching resulted in similar brightness development for both standard and HAI. Fibers bleached with chlorine dioxide had the highest curl index (16–17 %) compared to the fibers bleached with hydrogen peroxide (15 %).

Effects of black tea tooth staining previously to 35% hydrogen peroxide bleaching

Aim: To determine if the artificial staining with black tea (BT) influences the enamel microhardness before in-office bleaching and if BT staining is necessary to evaluate the efficacy of bleaching with 35% hydrogen peroxide Methods: Enamel/dentin blocks were randomized into groups according to the staining protocol (n=5/group): (CO) control – maintained in artificial saliva solution (AS); (BT4) immersed in black tea solution for 4 h; (BT24) immersed in black tea solution for 24 h. After the staining protocols, all specimens were kept in AS for one week, followed by bleaching (three sessions of HP application for 40 min). Knoop surface microhardness (kgF/mm2) was determined at baseline (T0), after staining (T1), after 7 days of storage in AS (T2), and after bleaching (T3). The color (ΔE00) and coordinate changes (ΔL, Δa, Δb) were measured using a digital spectrophotometer at T0 and T3. Data were submitted to one-way (ΔE00, ΔL, Δa, Δb) or two-way ANOVA repeated measures (kgF/mm2) and Tukey’s test (a=5%). Results: The staining protocols (BT4 and BT24) promoted significantly lower microhardness (T1 and T2, p&lt;0.05) than CO, whereas CO was the only group to maintain microhardness values over time. Bleaching promoted perceptible ΔE00 without a significant difference among the groups regardless of the staining protocol (p=0.122). CO and BT4 showed no differences in terms of ΔL and Δa (p&gt;0.05), but BT4 displayed a higher Δb than CO. Conclusion: The artificial staining with BT negatively affected the enamel surface microhardness and was not essential to evaluate the efficacy of 35% hydrogen peroxide bleaching.