Significance
Rock varnish is a prominent feature of desert landscapes and the canvas for many prehistoric petroglyphs. How it forms—and, in particular, the basis for its extremely high manganese ...content—has been an enduring mystery. The work presented here establishes a biological mechanism for this manganese enrichment, underpinned by an apparent antioxidant strategy that enables microbes to survive in the harsh environments where varnish forms. The understanding that varnish is the residue of life using manganese to thrive in the desert illustrates that, even in extremely stark environments, the imprint of life is omnipresent on the landscape.
Desert varnish is a dark rock coating that forms in arid environments worldwide. It is highly and selectively enriched in manganese, the mechanism for which has been a long-standing geological mystery. We collected varnish samples from diverse sites across the western United States, examined them in petrographic thin section using microscale chemical imaging techniques, and investigated the associated microbial communities using 16S amplicon and shotgun metagenomic DNA sequencing. Our analyses described a material governed by sunlight, water, and manganese redox cycling that hosts an unusually aerobic microbial ecosystem characterized by a remarkable abundance of photosynthetic Cyanobacteria in the genus
Chroococcidiopsis
as the major autotrophic constituent. We then showed that diverse Cyanobacteria, including the relevant
Chroococcidiopsis
taxon, accumulate extraordinary amounts of intracellular manganese—over two orders of magnitude higher manganese content than other cells. The speciation of this manganese determined by advanced paramagnetic resonance techniques suggested that the Cyanobacteria use it as a catalytic antioxidant—a valuable adaptation for coping with the substantial oxidative stress present in this environment. Taken together, these results indicated that the manganese enrichment in varnish is related to its specific uptake and use by likely founding members of varnish microbial communities.
ABSTRACT The purpose of this study is to determine the varnish layer hardness and varnish adhesion strength of the varnished Crimean juniper (Juniperus excelsa M. Bieb.) wood growing naturally in the ...Kastamonu region of Turkey. Test samples were varnished with UV-resistant polyurethane alkyd resin high gloss varnish (PAV) and water-based acrylic resin gloss varnish (WBAV). The varnish adhesion strength test was carried out by using universal testing machine. The varnish layer hardness was measured by using König pendulum hardness tester. Additionally, the colour properties were measured by spectrophotometer equipment that used the L*a*b* colour space. The adhesion strength of the polyurethane varnish and the water-based varnish were determined 2.81 MPa and 2.25 MPa respectively. Surface hardness value for water-based varnish and polyurethane varnish were determined 71 and 25 oscillation respectively. Detecting the performance of polyurethane and water-based varnish applications for the Crimean juniper wood will provide guidance in which type of varnish will be better for finishing. As a result, in varnish applications of the wood, it is recommended that water-based acrylic varnish should be applied when surface hardness is required. In addition, polyurethane alkyd varnish should be applied when better surface adhesion strength is desired.
•Zinc-oxide nanoparticles (ZnO-NP) effectively inhibits S. mutans growth at 0.53 μg/mL.•ZnO-NP showed anti-biofilm, acid-inhibiting and anti-oxidant properties.•ZnO-NP varnish has anti-caries ...potential for being antimicrobial against S. mutans.
Zinc is a potent antimicrobial against cariogenic bacteria and effective anti-plaque agent. The present study investigated the efficacy of zinc oxide nanoparticles (ZnO-NP) varnish to inhibit S. mutans growth, biofilm, acid production, and its antioxidant potential and cytotoxicity.
Green synthesized ZnO-NP were characterized using ultraviolet–visible spectroscopy, x-ray diffraction spectroscopy, and transmission electron microscopy. Secondary metabolites were assessed using fourier transform infrared spectroscopy. Anti-oxidant potential was ascertained using 2,2-diphenyl-2-picrylhydrazyl hydrate (DDPH) assay and cytotoxicity of synthesized nanoparticles was evaluated on human liver cancer (Hep G2) and human embryonic kidney 293 (HEK-293T) cell lines.
Synthesized ZnO-NP showed excellent antimicrobial properties against S. mutans, as the minimum inhibitory and bactericidal concentrations were 0.53 μg/mL, and 1.3 μg/mL respectively. ZnO-NP at 0.1 mg/μl concentration had the greatest zone of inhibition (24 mm), followed by 0.05 mg/μl ZnO-NP (23 mm) and 0.05 mg/μl ampicillin (21 mm). Further, 0.1 mg/μl ZnO-NP varnish inhibited 90 % of S. mutans biofilms and reduced 24 h acid production closest to that of baseline and it also exhibited antioxidant capacity in a dose dependent manner (94 % inhibition-100 μg/mL). Biocompatibility of ZnO-NP varnish was evaluated on Hep G2 and HEK-293T cell lines; and the highest concentration of 0.1 mg/μl ZnO-NP used caused very low cytotoxicity to Hep G2 cells and was non-cytotoxic to HEK-293T cells.
Within the limits of this study, ZnO-NP varnish was effective in inhibiting S. mutans and holds great potential as an effective anticaries agent.
The important factors contributing to the effectiveness of fluoride varnish are the amount of fluoride ion release and the retention time of the varnish on the tooth surface. Commercial fluoride ...varnishes are susceptible to mechanical removal; therefore, patients are informed to avoid eating or performing oral hygiene for at least 12–24 h, which results in patient inconvenience. However, cyanoacrylate-based fluoride varnish would not have these disadvantages. This study compared the daily fluoride ion release, abrasion resistance to brushing, and toxicity to human gingival fibroblasts (hGFs) between a newly-developed cyanoacrylate-based fluoride varnish and conventional fluoride varnish (Duraphat varnish). The results demonstrated that the cyanoacrylate varnish had a significantly higher fluoride release for 9 days after application, higher abrasion resistance to brushing, and slightly less toxicity to hGFs compared with Duraphat varnish. This novel cyanoacrylate varnish could be an alternative fluoride varnish for preventing dental caries.
We investigated rock varnishes collected from several locations and environments worldwide by a broad range of microanalytical techniques. These techniques were selected to address the challenges ...posed by the chemical and structural complexity within the micrometer- to nanometer-sized structures in these geological materials. Femtosecond laser ablation-inductively coupled plasma-mass spectrometry (fs LA-ICP-MS), scanning transmission X-ray microscopy-near edge X-ray adsorption fine structure spectroscopy (STXM-NEXAFS) in combination with scanning electron microscopy (SEM) of focused ion beam (FIB) ultra-thin (100–200nm) sections, conventional and polarization microscopy, as well as electron paramagnetic resonance (EPR) measurements were used to obtain information about these rock varnishes.
Rock varnishes from different environments, which cannot readily be distinguished based on their macroscopic appearance, differ significantly in their constituent elemental mass fractions, e.g., of Mn, Fe, Ni, Co, Ba, and Pb, and their rare earth element (REE) patterns. Structural characteristics such as the particle sizes of embedded dust grains, internal structures such as layers of Mn-, Fe-, and Ca -rich material, and structures such as cavities varied between varnishes from different environments and regions in the world. The EPR spectra were consistent with aged biogenic Mn oxides in all samples, but showed subtle differences between samples of different origin.
Our observations allow us to separate rock varnishes into different types, with differences that might be indicators of distinct geneses. Five different types of rock varnish could be distinguished, Type I–V, of which only Type I might be used as potential paleoclimate archive. Each varnish type has specific characteristics in terms of their elemental composition, element distribution, and structures. The combination of element ratios (Mn/Ba, Al/Ni, Mn/REY, Mn/Ce, Mn/Pb, LaN/YbN, and Ce/Ce*), total REE contents, and structures can be used to separate the different types of rock varnish from each other.
Thermal stability on air of polyurethane varnish coating prepared from diphenylolpropane, polyetherpolyol and polyisocyanate was assessed. The presence of urethane groups, formed by phenolic hydroxyl ...of diphenylolpropane, in the polymer structure was shown to decrease its thermooxidative degradation onset temperature. At the same time, deceleration of thermooxidative processes due to stabilizing effect of diphenylolpropane released at the beginning of thermal decay of polyurethane is observed in the higher temperature region.
AimTo study the effect of combination of chlorhexidine and Fluoride on the growth and colonization of cariogenic bacteria (Streptococcus mutans) in children with mixed dentition. Materials and ...methodsSixty children of age 6-14 years with mixed dentition and S. mutans count > 1 × 105 CFU/mL of saliva were divided: group I-chlorhexidine varnish; group II-Fluoride varnish; group III-Combination of chlorhexidine and Fluoride varnish. chlorhexidine and Fluoride varnishes were applied to teeth once every week for four consecutive weeks in respective groups. Salivary S. mutans count was estimated and evaluated at baseline, 1, 3, and 6 months. ResultsNo significant difference was seen in group I and II at the end of 1, 3, and 6 months (p > 0.001) but the reduction in S. mutans count was statistically more significant in group III after a period of 6 months (p < 0.001). Maximum reduction in count was noted in group III at all intervals of varnish application. ConclusionThe concomitant use of chlorhexidine and fluoride varnish would prove to be more effective than individual components over a longer period of time and especially in high caries risk children. How to cite this articleMore VP, Hugar SM, Sogi S, et al. Comparative Evaluation of the Efficacy of Chlorhexidine, Fluoride and the Combined Use of Chlorhexidine and Fluoride Varnishes on Salivary Streptococcus mutans Count in Children with Mixed Dentition: An In Vivo Study. Int J Clin Pediatr Dent 2022;15(3):267-272.
The objective of this study was to investigate the gloss of different types of commercially manufactured varnish systems, including water-based (WB), polyurethane (PUR) and UV-cured (UV), applied on ...veneered MDF panels with sanded and thermally densified alder and birch wood veneers. The varnishes were applied at various numbers of layers on veneered panels. The gloss was measured at three angles of incident light: 20°, 60° and 85°. Statistical analysis showed that the type of varnish, the number of layers, the pre-treatment process, the wood species and direction of wood fibers significantly affect gloss of the coatings of veneered MDF panels. The type of varnish had a dominant effect on gloss. The highest gloss values were measured for the UV-varnished surface, and the lowest for WB- and PUR-varnished surfaces. Gloss was enhanced with an increase in the number of layers. Birch veneer provided higher gloss values compared to alder veneer. The gloss values measured along the wood fibers were higher than those measured across the fibers. No significant differences were found between the coatings created on sanded and thermally densified veneers for the average gloss values measured along the fibers at angles 60° and 85°. This study could have practical applications for producing value-added furniture elements using low-value wood species pre-treated by thermal compression.
Rocks in arid to semi-arid regions all over the world have a naturally occurring coating called “rock varnish” or “desert varnish” on their surface. These lustrous, black-to-brown mesoscopic coatings ...on rocks have long piqued the interest of scholars from a wide range of disciplines. However, there are gaps in our understanding, particularly in relation to the formation of rock varnish. Rock varnish development is supported by competing evidence from the biotic and abiotic schools of thought. In the current investigation, we advance and support a previous polygenetic model by proposing that biotic and abiotic factors collaborate to form these microscopic coatings on the rock surfaces. Physicochemical evidences in this work points toward a new perspective, citing an initial abiotic triggering event followed by biotic processes.
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•New insight: Ladakh's rock varnish forms through polygenetic genesis—abiotic triggers, followed by biotic collaboration.•Surface wettability shifts to hydrophobic, promoting a microbial favourable environment during varnish formation.•Mn abundance in varnish layer, along with Ba, Cu, Zn, Pb, Y, Th, and U, suggests non-crustal origin and abiotic synthesis.•LREEs (Nd, Sm, Eu) in varnish are 4 to 6 times more abundant than other REEs, implying microbial mediation in their enrichment.
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