The purpose of this study was to determine the efficacy of fluoride varnish (5% sodium fluoride, Duraphat®, Colgate) in reverting white spot lesions (WSLs) after fixed orthodontic treatment. This study was a randomized, parallel group, controlled clinical trial. Using saline solution as control, 110 participants (mean age ± standard deviation: 16.6±3.2 years) ranging from 12 to 22 years old were randomly assigned to either the test group (group 1) or the control group (group 2). Application of fluoride varnish or saline was applied onto tooth surfaces with WSLs every month during the first 6 months after debonding. The labial (buccal) surfaces of the teeth were assessed by the use of a DIAGNOdent pen (DD) at the baseline, 3- and 6-month follow-up visits. After 6 months, 96 subjects with a total of 209 study teeth (47 subjects, 104 teeth in group 1; 49 subjects, 105 teeth in group 2) remained. The WSLs had a mean DD reading at baseline of 17.66±5.36 in group 1 and 16.19±5.70 in group 2, which decreased by 5.78 and 2.44, respectively, at the 3-month follow-up visit and decreased by 7.56 and 3.09, respectively, at the 6-month follow-up visit. The mean baseline DD readings in the two groups were similar (t test, P>0.05). There was statistically significant differences between the mean DD readings of the two groups at the 3-month (P<0.05) and at the 6-month follow-up visits (P<0.01). Topical fluoride varnish application is effective in reversing WSLs after debonding and should be advocated as a routine caries prevention measure after orthodontic treatment.

concentration has increased from ≈277 ppm in 1750, prior to Industrial Revolution, to ≈410 ppm in 2019 and the average annual growth of carbon emission in 2018 and 2019 is greater than its 10-year average. [1] Thus, it is urgent to search for renewable and zero-carbon energy sources as alternatives to replace fossil fuels. [2] Although solar, wind and tidal energy are abundant and sustainable, their intermittent and weather-dependent limitations require development and deployment of highly efficient energy conversion and storage systems at large scale to bridge the time gap between supply and demand. [3] An attractive solution is to convert the electrical energy derived from the aforementioned renewable energy sources into chemical energy in the form of hydrogen. [4,5] Pure or mixed hydrogen is playing important roles in transportation, industrial sectors, and chemical transformation processes. [6] However, at present, 95% of hydrogen is still produced by reforming of fossil fuels that emits significant amount of CO 2 and only 4% is through water electrolysis, mainly owing to the much higher production cost of the latter. [7] Therefore, crucial to enable this sustainable vision is to improve the efficiency and scalability of water electrolysis technology.

Wide-band gap (WBG) mixed-halide perovskites have drawn much attention because of their excellent optoelectronic properties and the potential to be deployed in tandem solar cells. Nevertheless, the bromine incorporation inevitably leads to photoinduced phase segregation in WBG mixed-halide perovskites. Herein, potassium is used to effectively suppress photoinduced phase segregation, which is visualized with confocal photoluminescence microscopy imaging. Strikingly, the potassium passivation not only inhibits the formation of the narrow-band gap subphase but also enhances the crystallinity of the WBG mixed-halide perovskite. In addition, the potassium-passivated WBG perovskite exhibits lower defect density, longer charge carrier lifetime, and better photostability. As a result, the optimized KI (2 mol %)-passivated WBG perovskite solar cells (PSCs) deliver a champion power conversion efficiency of 18.3% with negligible hysteresis. They maintain 98% of their initial efficiency after 400 h under 100 mW•cm −2 white light illumination in nitrogen.

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A headspace single-drop microextraction (SDME) based on ionic liquid (IL) has been developed for the gas chromatographic determination of phenols. The volume of IL microdrop used was 1 microL. After extraction, the analytes were desorbed from the drop in the injection port and the involatile IL was withdrawn into the microsyringe. To facilitate the withdrawal of IL the upper diameter of the split inlet liner was enlarged to some extent. Some parameters were optimized for the determination of phenols. Under the selected conditions, i.e., desorption for 100 s at 210 degrees C after extraction for 25 min at 50 degrees C in solutions (pH 3) containing 0.36 g/mL sodium chloride, the LODs, RSDs, and the average enrichment factors of phenols were 0.1-0.4 ng/mL, 3.6-9.5% (n=5), and 35-794, respectively. The proposed procedure was applied to the determination of phenols in lake water and wastewater samples, and the spiked recoveries were in the range of 81-111% at a spiked level of 0.4 microg/mL. This method is a promising alternative for the sensitive determination of phenolic compounds.