Metal Content in Textile and (Nano)Textile Products

Metals, metallic compounds, and, recently, metallic nanoparticles appear in textiles due to impurities from raw materials, contamination during the manufacturing process, and/or their deliberate addition. However, the presence of lead, cadmium, chromium (VI), arsenic, mercury, and dioctyltin in textile products is regulated in Europe (Regulation 1907/2006). Metal determination in fabrics was performed by inductively coupled plasma-mass spectrometry (ICP-MS) after microwave-assisted acid digestion. The ICP-MS procedure has been successfully validated; relative standard deviations were up to 3% and analytical recoveries were within the 90-107% range. The developed method was applied to several commercial textiles, and special attention has been focused on textiles with nanofinishing (fabrics prepared with metallic nanoparticles for providing certain functionalities). Arsenic content (in textile T4) and lead content (in subsamples T1-1, T1-2, and T3-3) were found to exceed the maximum limits established by the European Regulation 1907/2006. Although impregnation of yarns with mercury compounds is not allowed, mercury was quantified in fabrics T1-2, T5, and T6. Further speciation studies for determining hexavalent chromium species in sample T9 are necessary (hexavalent chromium is the only species of chromium regulated). Some textile products commercialised in Europe included in this study do not comply with European regulation 1907/2006.

The micro-shear bond strength of resin cements to aged laser bleached enamel after using different desensitizing agents

Objectives

To evaluate the micro‐shear bond strength of two resin cements to aged laser bleached enamel after the application of three different desensitizing agents.

Materials and methods

Forty extracted human central and lateral incisors were prepared and bleached using laser activation bleaching protocol. The teeth were assigned randomly into four groups for desensitization; G1: No post‐bleaching treatment, G2: GC MI Paste Plus, G3: Hydroxyapatite nanoparticles (n‐HAP) and G4: Flor‐Opal. Specimens were subjected to aging for 6 months. All groups were subdivided into two subgroups according to the resin cements used (dual‐curing resin cement and light‐curing resin cement).

Results

Flor‐Opal groups showed the highest statistically significant micro‐shear bond strength (MSBS), followed by GC MI Paste Plus and n‐HAP groups with no statistically significant difference between them. The light‐curing resin cement had statistically higher MSBS than dual‐curing resin cement in case of no‐post bleaching treatment and n‐HAP groups, and no statistical difference in case of GC MI Paste Plus and Flor‐Opal groups.

Conclusion

Usage of desensitizing agents containing, CPP‐ACP, n‐HAP or fluoride after laser bleaching can enhance the bond strength of the resin cements to enamel.

Clinical significance

The composition of the desensitizing agents applied after laser bleaching could interfere in bond strength values.

Scalable Preparation of Cellulose Nanofibers from Office Waste Paper by an Environment-Friendly Method

Waste paper is often underutilized as a low-value recyclable resource and can be a potential source of cellulose nanofibers (CNFs) due to its rich cellulose content. Three different processes, low acid treatment, alkali treatment and bleaching treatment, were used to pretreat the waste paper in order to investigate the effect of different pretreatments on the prepared CNFs, and CNFs obtained from bleached pulp boards were used as control. All sample fibers were successfully prepared into CNFs by 2,2,6,6-tetramethyl-piperidine-1-oxyl (TEMPO) oxidation. It was quite obvious that the bleached CNFs samples showed dense fibrous structures on a scanning electron microscopy (SEM), while needle-like fibers with width less than 20 nm were observed on a transmission electron microscopy (TEM). Meanwhile, the bleaching treatment resulted in a 13.5% increase in crystallinity and a higher TEMPO yield (e.g., BCNF, 60.88%), but a decrease in thermal stability. All pretreated CNFs samples showed narrow particle size distribution, good dispersion stability (zeta potential less than −29.58 mV), good light transmission (higher than 86.5%) and low haze parameters (lower than 3.92%). This provides a good process option and pathway for scalable production of CNFs from waste papers.

Effects of tooth bleaching protocols assisted by Er,Cr:YSGG and diode (980 nm) lasers on color change of resin-based restoratives

OBJECTIVE

To evaluate color change of three resin-based restorative materials after two laser-assisted in-office tooth bleaching protocols using Er,Cr:YSGG and diode (980 nm) lasers.

MATERIALS AND METHODS

A nanohybrid composite resin (EP), a Bis-GMA free composite resin (EPBio) and a resin-matrix CAD-CAM ceramic (HC) were tested. Ninety specimens were prepared and stored in artificial saliva. Group 1 received an in-office bleaching treatment using 40% H₂ O_2. The same bleaching procedure was assisted by Er,Cr:YSGG laser in Group 2 and by a diode laser (980 nm) in Group 3. Color measurements were performed using a double-beam UV-Vis spectrophotometer at four time intervals (before, 24 h, 15 and 30 days), converted to L*, a*, and b* units of the CIELAB color space and assessed on the basis of 50:50% acceptability (ΔΕ_ab * = 2.7 and ΔΕ₀₀  = 1.77) and 50:50% perceptibility (ΔΕ_ab * = 1.2 and ΔΕ₀₀  = 0.81) thresholds. Three-way ANOVA with repeated measurements was used for statistical analysis of the data.

RESULTS

Color and whiteness changes did not exceed the established 50:50% acceptability thresholds. EP presented the highest color change after the bleaching followed by EPBio and HC (p ≤ 0.05). Three-way ANOVA revealed that type of material and time interval significantly affected color change (p ≤ 0.001).

CONCLUSIONS

The tested bleaching treatments assisted by Er,Cr:YSGG and diode (980 nm) lasers did not induce unacceptable color and whiteness changes in the resin-based restorative materials.

CLINICAL SIGNIFICANCE

The tested Er,Cr:YSGG and diode (980 nm) laser-assisted tooth bleaching protocols which may be recommended to accelerate the clinical procedures cannot affect the color of the existing resin-based restorations in case they are accidentally exposed on the bleaching gel and laser irradiation.

A portfolio of climate-tailored approaches to advance the design of marine protected areas in the Red Sea

Intensified coastal development is compromising the health and functioning of marine ecosystems. A key example of this is the Red Sea, a biodiversity hotspot subjected to increasing local human pressures. While some marine-protected areas (MPAs) were placed to alleviate these stressors, it is unclear whether these MPAs are managed or enforced, thus providing limited protection. Yet, most importantly, MPAs in the Red Sea were not designed using climate considerations, likely diminishing their effectiveness against global stressors. Here, we propose to tailor the design of MPAs in the Red Sea by integrating approaches to enhance climate change mitigation and adaptation. First, including coral bleaching susceptibility could produce a more resilient network of MPAs by safeguarding reefs from different thermal regions that vary in spatiotemporal bleaching responses, reducing the risk that all protected reefs will bleach simultaneously. Second, preserving the basin-wide genetic connectivity patterns that are assisted by mesoscale eddies could further ensure recovery of sensitive populations and maintain species potential to adapt to environmental changes. Finally, protecting mangrove forests in the northern and southern Red Sea that act as major carbon sinks could help offset greenhouse gas emissions. If implemented with multinational cooperation and concerted effort among stakeholders, our portfolio of climate-tailored approaches may help build a network of MPAs in the Red Sea that protects more effectively its coastal resources against escalating coastal development and climate instability. Beyond the Red Sea, we anticipate this study to serve as an example of how to improve the utility of tropical MPAs as climate-informed conservation tools.

Color Stability and Staining Susceptibility of Direct Resin-Based Composites after Light-Activated In-Office Bleaching

This study evaluated color stability and staining susceptibility of five direct resin-based composites (RBCs) subjected to light-activated in-office bleaching with 40% hydrogen peroxide (HP). The test materials included 5 RBCs, which consisted of one nano-filled, one sub-micron, one bulk-filled, and two nano-hybrid RBC types. Ten disc-shaped specimens of each RBC were fabricated and divided into bleaching (BLE) and non-bleaching (CON) groups (n = 5 for each group). Specimens were then immersed in red wine solution over 4 h. A spectrophotometer was used to obtain Commission Internationale de l'Eclairage (CIE) L*a*b* parameters for each of the following periods tested: before bleaching (T_BA), after bleaching (T_BL), and after staining (T_ST). Color stability and staining susceptibility were evaluated using two metrics, CIEDE2000 color differences (ΔE₀₀) and whiteness variations using the whiteness index (ΔWI_D). Data were analyzed using repeated measures two-way analysis of variance (ANOVA) (α = 0.05). Statistically significant and clinically unaccepted ΔE₀₀ and ΔWI_D were observed for all tested specimens between T_BA and T_BL. The nano-hybrid type RBCs showed the highest discoloration among materials after bleaching treatment. The BLE group exhibited significantly higher ΔE₀₀ and ΔWI_D than the CON group for all the tested RBCs between T_BA and T_ST. The sub-micron type RBC showed the highest discoloration among materials after immersion in the red wine. Conclusion. The light-activated in-office bleaching with 40% HP's influences on color and whiteness index were material-dependent. The use of bleaching treatment also increased the susceptibility to red wine for all RBCs.

Knowledge, Practices, and Perceptions about Tooth Whitening among Female Population in Saudi Arabia - A Cross-Sectional Study

Background:

Tooth-whitening procedures have gained wide popularity among the Saudi population. The present study aimed to assess the knowledge, attitude, and perception about tooth-whitening procedures among Jeddah's general population.

Materials and Methods:

A face-to-face interview was conducted on randomly selected female patients attending dental clinics. A pretested and structured questionnaire was used to record the response by calibrated interviewers. The responses regarding knowledge, attitude, and perceptions were recorded and subjected to statistical analysis.

Results:

The findings showed that the prevalence of tooth whitening among the participants was 43.7%, and about 8.7% reported that they did it once every year. In-office bleaching was the most preferred method (31.4%), followed by whitening toothpaste (8.7%). An increased frequency of bleaching was reported by participants belonging to younger age group (P < 0.001).

Conclusion:

The knowledge related to the mechanism of action and adverse effects was average among the participants. Younger age groups were more concerned about tooth-whitening procedures compared to the older ones.

Effect of staining and bleaching on the microhardness, surface roughness and color of different composite resins

BACKGROUND

There are studies that examined the effect of staining on the surface properties of composite resins, using different solutions and bleaching applications. However, the effect of both staining and bleaching on the same composite specimens is an issue that needs to be investigated.

OBJECTIVES

The aim of this study was to investigate the surface microhardness, roughness and color changes (ΔE) of 2 different composite resins after staining and bleaching.

MATERIAL AND METHODS

A microhybrid and a nanohybrid composite were used in the study. One hundred and fifty specimens were prepared from each composite. The specimens were divided into 5 groups and stained for 30 days with tea, coffee, cola, red wine, or distilled water (control). Subsequently, each group was divided into 3 subgroups. Each subgroup received a 14-day application of Opalescence™ Boost, Opalescence PF or VivaStyle® Paint On Plus bleaching materials. The color as well as surface microhardness and roughness of all specimens were determined at baseline, after staining and after bleaching. Data was analyzed using the repeated-measures analysis of variance (ANOVA) and the Bonferroni method.

RESULTS

A statistically significant decrease was observed in the surface microhardness of the microhybrid composite specimens after bleaching (p < 0.05).The highest ΔE values were observed in the red wine groups for both composite resins.

CONCLUSIONS

Staining and bleaching may affect surface properties and color, depending on the type, filler and matrix content of the composite resin.

Prevalence and Photobiology of Photosynthetic Dinoflagellate Endosymbionts in the Nudibranch Berghia stephanieae

Simple Summary

Some sea slugs have evolved highly specialized feeding habits and solely prey upon a reduced number of species. This is the case of Berghia stephanieae, a sea slug that feeds exclusively on glass anemones, such as Exaiptasia diaphana. Glass anemones host photosynthetic microalgae that B. stephanieae ingest when preying upon E. diaphana. The association between these photosynthetic microalgae and sea slugs appears to be limited in time, particularly if B. stephanieae is deprived of prey hosting these microalgae. In the present study, we validate the use of a non-invasive and non-destructive approach that allows monitoring the persistence of this association in live sea slugs by measuring chlorophyll fluorescence. A complete loss of photosynthetic microalgae was observed within 8 days when animals were deprived of food or fed glass anemones with no microalgae (bleached anemones). As such, the association between B. stephanieae and photosynthetic microalgae acquired when preying glass anemones is not a true symbiosis. Future studies may use the technique here described to monitor the prevalence of the association between sea slugs and photosynthetic microalgae, particularly under bleaching events that will impair sea slugs to acquire microalgae by preying upon their invertebrate hosts.

Abstract

Berghia stephanieae is a stenophagous sea slug that preys upon glass anemones, such as Exaiptasia diaphana. Glass anemones host photosynthetic dinoflagellate endosymbionts that sea slugs ingest when consuming E. diaphana. However, the prevalence of these photosynthetic dinoflagellate endosymbionts in sea slugs appears to be short-lived, particularly if B.stephanieae is deprived of prey that host these microalgae (e.g., during bleaching events impacting glass anemones). In the present study, we investigated this scenario, along with food deprivation, and validated the use of a non-invasive and non-destructive approach employing chlorophyll fluorescence as a proxy to monitor the persistence of the association between sea slugs and endosymbiotic photosynthetic dinoflagellates acquired through the consumption of glass anemones. Berghia stephanieae deprived of a trophic source hosting photosynthetic dinoflagellate endosymbionts (e.g., through food deprivation or by feeding on bleached E. diaphana) showed a rapid decrease in minimum fluorescence (F_o) and photosynthetic efficiency (F_v/F_m) when compared to sea slugs fed with symbiotic anemones. A complete loss of endosymbionts was observed within 8 days, confirming that no true symbiotic association was established. The present work opens a new window of opportunity to rapidly monitor in vivo and over time the prevalence of associations between sea slugs and photosynthetic dinoflagellate endosymbionts, particularly during bleaching events that prevent sea slugs from incorporating new microalgae through trophic interactions.

Polymeric biomaterials maintained the esthetic efficacy and reduced the cytotoxicity of in-office dental bleaching

Evaluate the kinetics of hydrogen peroxide (H₂ O₂ ) degradation, esthetic efficacy and cytotoxicity of a bleaching gel with 35%H₂ O₂ applied on enamel previously covered or not with polymeric nanofibrillar scaffold (SNan), polymeric primer catalyst (PPol), and both. Standardized enamel/dentin discs (n = 128) obtained from bovine teeth were adapted to pulp chambers. After covering enamel with the polymeric products, the bleaching gel was applied for 45 min, establishing the following groups: G1: no treatment (negative control); G2: 35%H₂ O₂ (positive control); G3: SNan; G4: PPol; G5: SNan + PPol; G6: SNan + 35%H₂ O₂ ; G7: PPol + 35%H₂ O₂ ; G8: SNan + PPol + 35%H₂ O₂ . The kinetics of H₂ O₂ degradation (n = 8), bleaching efficacy (ΔE/ΔWI; n = 8), trans-amelodentinal cytotoxicity (n = 8), and cell morphology (n = 4) were assessed (ANOVA/Tukey test; p < 0.05). Greater H₂ O₂ degradation occurred in G7 and G8. Bleaching efficacy (ΔE) was higher in G6, G7, and G8 in comparison with G2 (p < 0.05). However, no difference was observed for ΔWI (p > 0.05). G8 presented the lower level of trans-amelodentinal diffusion of H₂ O₂ , oxidative stress, and toxicity to the MDPC-23 cells (p < 0.05). Polymeric biomaterials increased the kinetics of H₂ O₂ decomposition, as well as maintained the esthetic efficacy and minimized the cytotoxicity caused by a bleaching gel with 35%H₂ O₂ . CLINICAL SIGNIFICANCE: Application of a bleaching gel with 35%H₂ O₂ on enamel previously covered by polymeric biomaterials maintains the esthetic efficacy and reduces the cytotoxicity caused by a single session of in-office dental bleaching.

Brooded coral offspring physiology depends on the combined effects of parental press and pulse thermal history

Reef-building corals respond to the temporal integration of both pulse events (i.e., heat waves) and press thermal history (i.e., local environment) via physiological changes, with ecological consequences. We used a "press-pulse-press" experimental framework to expose the brooding coral Porites astreoides to various thermal histories to understand the physiological response of temporal dynamics within and across generations. We collected adult colonies from two reefs (outer Rim reef and inner Patch reef) in Bermuda with naturally contrasting thermal regimes as our initial "press" scenario, followed by a 21-day ex situ "pulse" thermal stress of 30.4°C during larval brooding, and a "press" year-long adult reciprocal transplant between the original sites. Higher endosymbiont density and holobiont protein was found in corals originating from the lower thermal variability site (Rim) compared to the higher thermal variability site (Patch). The thermal pulse event drove significant declines in photosynthesis, endosymbiont density, and chlorophyll a, with bleaching phenotype convergence for adults from both histories. Following the reciprocal transplant, photosynthesis was higher in previously heated corals, indicating recovery from the thermal pulse. The effect of origin (initial press) modulated the response to transplant site for endosymbiont density and chlorophyll a, suggesting contrasting acclimation strategies. Higher respiration and photosynthetic rates were found in corals originating from the Rim site, indicating greater energy available for reproduction, supported by larger larvae released from Rim corals post-transplantation. Notably, parental exposure to the pulse thermal event resulted in increased offspring plasticity when parents were transplanted to foreign sites, highlighting the legacy of the pulse event and the importance of the environment during recovery in contributing to cross-generational or developmental plasticity. Together, these findings provide novel insight into the role of historical disturbance events in driving differential outcomes within and across generations, which is of critical importance in forecasting reef futures.

Global tropical reef fish richness could decline by around half if corals are lost

Reef fishes are a treasured part of marine biodiversity, and also provide needed protein for many millions of people. Although most reef fishes might survive projected increases in ocean temperatures, corals are less tolerant. A few fish species strictly depend on corals for food and shelter, suggesting that coral extinctions could lead to some secondary fish extinctions. However, secondary extinctions could extend far beyond those few coral-dependent species. Furthermore, it is yet unknown how such fish declines might vary around the world. Current coral mass mortalities led us to ask how fish communities would respond to coral loss within and across oceans. We mapped 6964 coral-reef-fish species and 119 coral genera, and then regressed reef-fish species richness against coral generic richness at the 1° scale (after controlling for biogeographic factors that drive species diversification). Consistent with small-scale studies, statistical extrapolations suggested that local fish richness across the globe would be around half its current value in a hypothetical world without coral, leading to more areas with low or intermediate fish species richness and fewer fish diversity hotspots.

Masking ability of bleach-shade resin composites using the multilayering technique

OBJECTIVE

Evaluate the masking ability of bleach-shade resin composites applied by multilayering techniques over colored substrates.

MATERIALS AND METHODS

Disc-shaped specimens were fabricated from bleach-shade resin composites using different multilayering techniques. Substrates were produced in opaque ceramic discs simulating colored substrates (A2, A3, A3.5, C2, C3, C4) and a bleached tooth (0M1). Color coordinates were obtained using a reflectance spectrophotometer. Color difference was calculated by CIEDE2000 using coordinates of 0 M1 ceramic as standard reference. Data were analyzed by one-way ANOVA and Tukey's post-hoc test (p ≤ 0.05). Masking ability interpretation was based on perceptibility and acceptability thresholds.

RESULTS

All combinations presented ΔE₀₀ above the acceptable threshold (ΔE₀₀ >1.8), ranging from 2.49 to 7.42, regardless of the restorative system, multilayering strategy or substrate color. Multilayering combinations placed over A2, A3 and A3.5 were moderately (1.8<ΔE₀₀ ≤3.6) and clearly unacceptable (3.6<ΔE₀₀ ≤5.4), combinations associated with C2, C3 and C4 were clearly unacceptable and, extremely unacceptable (ΔE₀₀ >5.4). Lower ΔE₀₀ was observed for combinations with 0.5 mm extra white enamel layer (2.49), or 1.0 mm white dentin layer (2.69), over A2 and A3.5 substrates. Lightness difference showed the greatest contribution to ΔE₀₀ .

CONCLUSIONS

Bleach-shade resin composite systems applied by the multilayering technique were not able to ensure effective masking ability.

CLINICAL SIGNIFICANCE

Bleach-shade resin composites applied with different combinations of the multilayering technique were not effective in masking colored substrates. Alternative strategies, techniques and dental materials should be explored to obtain acceptable masking.

Feeding and thermal conditioning enhance coral temperature tolerance in juvenile Pocillopora acuta

Scleractinian corals form the foundation of coral reefs by acquiring autotrophic nutrition from photosynthetic endosymbionts (Symbiodiniaceae) and use feeding to obtain additional nutrition, especially when the symbiosis is compromised (i.e. bleaching). Juvenile corals are vulnerable to stress due to low energetic reserves and high demand for growth, which is compounded when additional stressors occur. Therefore, conditions that favour energy acquisition and storage may enhance survival under stressful conditions. To investigate the influence of feeding on thermal tolerance, we exposed Pocillopora acuta juveniles to temperature (ambient, 27.4°C versus cool, 25.9°C) and feeding treatments (fed versus unfed) for 30 days post-settlement and monitored growth and physiology, followed by tracking survival under thermal stress. Feeding increased growth and resulted in thicker tissues and elevated symbiont fluorescence. Under high-temperature stress (31-60 days post-settlement; ca 30.1°C), corals that were fed and previously exposed to cool temperature had 33% higher survival than other treatment groups. These corals demonstrated reduced symbiont fluorescence, which may have provided protective effects under thermal stress. These results highlight that the impacts of feeding on coral physiology and stress tolerance are dependent on temperature and as oceans continue to warm, early life stages may experience shifts in feeding strategies to survive.

Natural antioxidants to restore immediate bond strength to bleached enamel: Systematic review and meta-analysis of in vitro studies

OBJECTIVE

To evaluate whether natural antioxidant treatment would enhance the immediate bond strength of dental adhesives to bleached enamel through a systematic review and meta-analysis.

MATERIALS AND METHODS

Two reviewers performed a literature search up to November 2019 in seven databases. Only in vitro studies that evaluated the effect of the application of natural antioxidants in the bond strength of dental adhesives to bleached enamel were included. Analyses were carried out using RevMan 5.3.5 (The Nordic Cochrane Centre, The Cochrane Collaboration, Copenhagen, Denmark). A global analysis was performed with random-effects models at a significance level of p < 0.05.

RESULTS

Twenty-four studies were included in the meta-analysis. Both in-office (p ˂ 0.001) and at-home (p ˂ 0.001) bleaching reduced the immediate bond strength. When compared to bleached enamel, all antioxidants improved the bond strength, but only grape seed extract/proanthocyanidin and lycopene restored it to the control values (p ˃ 0.05).

CONCLUSION

In vitro available evidence suggests that the use of natural antioxidants can be beneficial when performing immediate resin-based restorations after bleaching, however, these results should be taken with caution since they are based on medium and high risk of bias studies; low bias studies are needed to draw relevant conclusions.

CLINICAL SIGNIFICANCE

Despite the lack of clinical evidence, the present study confirms the benefits of applying natural antioxidant agents to enhance the in vitro bond strength when performing immediate esthetic restorations after bleaching. Since certain antioxidant agents proved more effective than others, clinical investigations may be focused on the ones that withhold the most promising results. The application of natural antioxidants after bleaching may enable immediate esthetic restorations to be performed.

Whitening effect of 35% hydrogen peroxide in simulation of tooth with orthodontic bracket

OBJECTIVE

To evaluate the color change and tooth whitening perception in 2 and 3 mm dental specimens simulating the orthodontic bracket for a 14-day period.

MATERIALS AND METHODS

Forty bovine tooth fragments (8 × 7 mm) of 2 mm (G2, n = 20) and 3 mm (G3, n = 20) were divided into Control (C: without bracket simulation and whitening) and Experimental (E: with composite resin simulating orthodontic bracket cementation area). Analyses of color change (ΔE₀₀ ) and perception of tooth whitening (WI_D ) were performed before (T₀ ) and after (T₁ ) the first bleaching session; before (T₂ ) and after (T₃ ) the second bleaching session; and after 7 days of the second bleaching session (T₄ ).

RESULTS

After 14 days (T4), ΔE₀₀ and WI_D showed similarity results, except for G2C and G3E_. The thickness did not influence the ΔE₀₀ and WI_D (G2C = G3C and G2E = G3E). The presence of orthodontic bracket did not interfere in the color change or tooth whitening perception after 14 days, except for comparison of G2C and G3E. Additionally, dentin thickness did not influence the color change.

CLINICAL SIGNIFICANCE

Teeth with orthodontic brackets showed similar color change and whitening perception to teeth without orthodontic bracket, but it is not influenced by dentin thickness.

Nitrogen-Doped Titanium Dioxide Mixed with Calcium Peroxide and Methylcellulose for Dental Bleaching under Visible Light Activation

The available tooth whitening products in the market contain high concentrations of hydrogen peroxide (H₂O₂) as an active ingredient. Therefore, in order to curb the high H₂O₂ concentration and instability of liquid H₂O₂, this study evaluated the efficacy and cytotoxicity of the bleaching gel composed of 10% calcium peroxide (CaO₂) and visible-light-activating nitrogen-doped titanium dioxide (N-TiO₂) with methyl cellulose as a thickener. Extracted bovine teeth were discolored using coffee and black tea stain solution and were divided into two groups (n = 6). Bleaching was performed thrice on each tooth specimen in both the groups, with one minute of visible light irradiation during each bleaching time. The CIELAB L*a*b* values were measured pre- and post-bleaching. The N-TiO₂ calcinated at 350 °C demonstrated a shift towards the visible light region by narrowing the band gap energy from 3.23 eV to 2.85 eV. The brightness (ΔL) and color difference (ΔE) increased as bleaching progressed each time in both the groups. ANOVA results showed that the number of bleaching significantly affected ΔE (p < 0.05). The formulated bleaching gel exhibits good biocompatibility and non-toxicity upon exposure to 3T3 cells. Our findings showed that CaO₂-based bleaching gel at neutral pH could be a stable, safe, and effective substitute for tooth whitening products currently available in the market.

Bleaching and skin-lightening practice among female students in South India: A cross-sectional survey

BACKGROUND

Bleaching with skin-lightening preparations is a common practice in our society. Particularly, a practice simply known as "bleaching"-referring to application of skin-lightening chemicals including ammonia, hydrogen peroxide, and hypochlorite, repeated at intervals, as a salon-based or home-based procedure appears wide-spread among young females in India. However, there is limited medical literature on "bleaching."

AIMS

We aimed to estimate the prevalence of "bleaching" among female students of our campus and to assess the knowledge, attitude, and practices regarding "bleaching" in the same population.

METHODS

A cross-sectional, questionnaire-based survey was conducted among the female students of the campus following a presurvey focus group discussion with a representative group. A pilot survey conducted to standardize the survey questionnaire showed a high reliability (Cronbach's alpha > 0.7). Descriptive statistical methods were used to assess survey results, and frequencies were presented as percentages.

RESULTS

A total of 880 valid responses were analyzed (age group 17-30 years, mean age-20.24 years). 34.77% had done "bleaching" at least once. 63.8% of respondents did not know the ingredients, and 40.5% did not know about the side effects of "bleaching." 60.06% of those who bleached had experienced an adverse effect. 58.18% respondents knew about "bleaching" from friends/relatives and 17% from parlors. Only 2.3% respondents had consulted a dermatologist, and only 22.8% had used sunscreens. Top motivation to bleach was to lighten facial hairs (19.5%), for a "lighter" complexion (15.1%) and achieve "glow" before a function (15.2%).

CONCLUSION

Facial skin and hair "bleaching" is common in our society, and awareness regarding "bleaching" is low even among educated youth.

In vitro efficacy of commercial and experimental proteolytic enzyme-based whitening dentifrices on enamel whitening and superficial roughness

OBJECTIVE

To evaluate the whiteness index (W_ID ) and surface roughness (Ra) of bovine enamel after simulated tooth brushing with different commercial and experimental whitening dentifrices.

MATERIALS AND METHODS

Cylindrical enamel bovine specimens were acid etched, stained, and divided in nine groups (n = 8): Colgate® Optic White®, Crest® Baking Soda and Peroxide, Arm and Hammer® Advanced White™ Extreme Whitening, Rembrandt® Deeply White® + Peroxide, Close up® White Attraction Natural Glow, Hinode Prowhite, and experimental dentifrice containing papain (PP), bromelain (PB), or papain and bromelain (PPB). Ra and W_ID were obtained initially and after 600, 1200, and 3,600 cycles of simulated tooth brushing. Data were analyzed using two-way analysis of variance test (α = 0.05).

RESULTS

Ra was significantly influenced by both dentifrice (p = 0.043) and period of tooth-brushing simulation (p < 0.001). Except for PP and PPB, all groups showed a statistically significant increase in Ra after simulated tooth brushing. After staining and brushing, none of the materials tested increased the initial W_ID .

CONCLUSIONS

The effect of commercial whitening dentifrices may be related to their high abrasiveness. Experimental formulations tested provided a similar effect without undesired wear of enamel. Whitening dentifrices only act through an abrasive effect rather than bleaching the tooth structures. When used, special care must be taken for avoid undesired wear of enamel. Experimental dentifrices provided similar removal of extrinsic stains without undesired abrasiveness; however, this effect may be due to the use of less aggressive abrasives in their formulations.

Impact of Menthol on Growth and Photosynthetic Function of Breviolum Minutum (Dinoflagellata, Dinophyceae, Symbiodiniaceae) and Interactions with its Aiptasia Host

Environmental change, including global warming and chemical pollution, can compromise cnidarian-(e.g., coral-) dinoflagellate symbioses and cause coral bleaching. Understanding the mechanisms that regulate these symbioses will inform strategies for sustaining healthy coral-reef communities. A model system for corals is the symbiosis between the sea anemone Exaiptasia pallida (common name Aiptasia) and its dinoflagellate partners (family Symbiodiniaceae). To complement existing studies of the interactions between these organisms, we examined the impact of menthol, a reagent often used to render cnidarians aposymbiotic, on the dinoflagellate Breviolum minutum, both in culture and in hospite. In both environments, the growth and photosynthesis of this alga were compromised at either 100 or 300 µM menthol. We observed reduction in PSII and PSI functions, the abundances of reaction-center proteins, and, at 300 µM menthol, of total cellular proteins. Interestingly, for free-living algae exposed to 100 µM menthol, an initial decline in growth, photosynthetic activities, pigmentation, and protein abundances reversed after 5-15 d, eventually approaching control levels. This behavior was observed in cells maintained in continuous light, but not in cells experiencing a light-dark regimen, suggesting that B. minutum can detoxify menthol or acclimate and repair damaged photosynthetic complexes in a light- and/or energy-dependent manner. Extended exposures of cultured algae to 300 µM menthol ultimately resulted in algal death. Most symbiotic anemones were also unable to survive this menthol concentration for 30 d. Additionally, cells impaired for photosynthesis by pre-treatment with 300 µM menthol exhibited reduced efficiency in re-populating the anemone host.

Efficiency of Teeth Bleaching after Regenerative Endodontic Treatment: A Systematic Review

The aim of this review is to evaluate of effectiveness of bleaching procedures used to treat discolored teeth subsequent to regenerative endodontic procedures (REPs) based on the review of in vitro and in vivo studies. This literature review was carried out according to the PRISMA guidelines. Four databases (PubMed, Scopus, the Cochrane Library, and Web of Science databases) were searched electronically, until 30 January 2020 without a year limit. The quality of studies was assessed using a modified methodological index for non-randomized studies. After analyzing 1405 studies, 6 in vitro and 9 in vivo studies were eligible for this review. In in vitro studies, effectiveness of bleaching was assessed in teeth discolored by antibiotic pastes, blood, and barrier materials in various combinations. In all analyzed studies, bleaching was effective in teeth discolored by antibiotic pastes as well as by blood and barrier materials. Of 26 treated teeth in the in vivo studies, 17 teeth were bleached successfully. In six cases, there was improvement of the shade. In three cases, bleaching was not sufficient. Bleaching material, techniques, and times differed between studies. Whitening of discolored teeth after REPs is achievable. However, to establish precise guidelines, further long-term clinical studies should be performed.

Divergent expression of hypoxia response systems under deoxygenation in reef-forming corals aligns with bleaching susceptibility

Exposure of marine life to low oxygen is accelerating worldwide via climate change and localized pollution. Mass coral bleaching and mortality have recently occurred where reefs have experienced chronic low oxygen events. However, the mechanistic basis of tolerance to oxygen levels inadequate to sustain normal functioning (i.e. hypoxia) and whether it contributes to bleaching susceptibility, remain unknown. We therefore experimentally exposed colonies of the environmentally resilient Acropora tenuis, a common reef-building coral from the Great Barrier Reef, to deoxygenation-reoxygenation stress that was aligned to their natural night-day light cycle. Specifically, the treatment involved removing the 'night-time O₂ buffer' to challenge the inherent hypoxia thresholds. RNA-Seq analysis revealed that coral possess a complete and active hypoxia-inducible factor (HIF)-mediated hypoxia response system (HRS) homologous to other metazoans. As expected, A. tenuis exhibited bleaching resistance and showed a strong inducibility of HIF target genes in response to deoxygenation stress. We applied this same approach in parallel to a colony of Acropora selago, known to be environmnetally susceptible, which conversely exhibited a bleaching phenotype response. This phenotypic divergence of A. selago was accompanied by contrasting gene expression profiles indicative of varied effectiveness of their HIF-HRS. Based on our RNA-Seq analysis, we propose (a) that the HIF-HRS is central for corals to manage deoxygenation stress and (b) that key genes of this system (and the wider gene network) may contribute to variation in coral bleaching susceptibility. Our analysis suggests that heat shock protein (hsp) 70 and 90 are important for low oxygen stress tolerance and further highlights how hsp90 expression might also affect the inducibility of coral HIF-HRS in overcoming a metabolic crisis under deoxygenation stress. We propose that differences in coral HIF-HRS could be central in regulating sensitivity to other climate change stressors-notably thermal stress-that commonly drive bleaching.

The Effects of Unbleached and Bleached Nanocellulose on the Thermal and Flammability of Polypropylene-Reinforced Kenaf Core Hybrid Polymer Bionanocomposites

The thermal, thermo-mechanical and flammability properties of kenaf core hybrid polymer nanocomposites reinforced with unbleached and bleached nanocrystalline cellulose (NCC) were studied. The studied chemical composition found that unbleached NCC (NCC-UB) had 90% more lignin content compared to bleached NCC (NCC-B). Nanocelluloses were incorporated within polypropylene (PP) as the matrix, together with kenaf core as a main reinforcement and maleic anhydride grafted polypropylene (MAPP) as a coupling agent via a melt mixing compounding process. The result showed that the thermal stability of the nanocomposites was generally affected by the presence of lignin in NCC-UB and sulfate group on the surface of NCC-B. The residual lignin in NCC-UB appeared to overcome the poor thermal stability of the composites that was caused by sulfation during the hydrolysis process. The lignin helped to promote the late degradation of the nanocomposites, with the melting temperature occurring at a relatively higher temperature of 219.1 °C for PP/NCC-UB, compared to 185.9 °C for PP/NCC-B. Between the two types of nanocomposites, PP/NCC-B had notably lower thermo-mechanical properties, which can be attributed to the poor bonding and dispersion properties of the NCC-B in the nanocomposites blend. The PP/NCC-UB showed better thermal properties due to the effect of residual lignin, which acted as a compatibilizer between NCC-UB and polymer matrix, thus improved the bonding properties. The residual lignin in PP/NCC-UB helped to promote char formation and slowed down the burning process, thus increasing the flame resistance of the nanocomposites. Overall, the residual lignin on the surface of NCC-UB appeared to aid better stability on the thermal and flammability properties of the nanocomposites.

A Spectrophotometric Study on Light Attenuation Properties of Dental Bleaching Gels: Potential Relevance to Irradiation Parameters

Background: During in-office bleaching, appropriate light sources are applied in order to enhance the activity of the bleaching gels applied onto teeth. For this method to be effective, a high absorption of light within the gel is necessary. Variation in the light attenuation capability of the gel, the duration of application and light activation can contribute towards safety hazards associated with this procedure. Methods: In this study, seven different gels and hydrogen peroxide have been evaluated for their optical properties by means of spectrophotometry (440–1000 nm). The transmitted light spectrum was used to estimate the intensity loss for each gel. The mean intensity decreases observed were statistically analysed using an analysis of variance (ANOVA). Results: The five more-pigmented gels tested indicated a very similar intensity loss of around 80%, whereas the remaining two gels showed significantly less attenuation (predominantly, p < 10⁻⁶). Conclusions: Throughout the spectrum of wavelengths examined, and according to the underlying studies evaluated, five of the gels assessed demonstrated an attenuation high enough to possibly avoid overheating of the underlying enamel dentine and pulp. An evaluation of appropriate irradiation parameters is proposed.

Immobilization of peroxidase on textile carrier materials and their application in the bleaching of colored whey

Textiles represent promising support materials for enzymes. The goal of the present work was to investigate the immobilization of commercial peroxidase on a polyester needle felt and the repeated use in the gentle degradation of norbixin in whey from dairy cheese as a practical application. High enzyme loads were obtained by a 2-step immobilization procedure. First, the number of functional groups on the textile surface was increased by a modification with amino-functional polyvinylamine. Second, the enzyme was immobilized by using 2 types of crosslinking agents. Due to the iron content of peroxidase, inductively coupled plasma-optical emission spectrometry was used for the quantitative determination of the enzyme load on the textile. The enzyme activity was evaluated using common 2,2'-azino-di-(3-ethylbenzthiazoline-6-sulfonic acid) assay for peroxidases. By the variation of enzyme input and crosslinker concentration, a maximal enzyme load of 80 mg/g of textile was achieved, and a maximum specific activity of 57 U/g of textile. For the visualization of the enzyme on the fiber surface, fluorescence microscopy as well as scanning probe microscopy were used. The immobilized peroxidase showed significant activity, even after 50 reuse cycles. In addition, the potential of the new support and enzyme combination in commercial whey bleaching was demonstrated successfully on a 10-L scale.