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Background. Any decrease in friction between orthodontic wire and bracket can accelerate tooth movement in the sliding technique and result in better control of anchorage. This study was carried out to evaluate frictional forces by coating orthodontic wires and porcelain brackets with zinc oxide nanoparticles (ZnO).Methods. In this in vitro study, we evaluated a combination of 120 samples of 0.019×0.025 stainless steel (SS) orthodonticwires and 22 mil system edgewise porcelain brackets with and without spherical zinc oxide nanoparticles. Spherical ZnOnanoparticles were deposited on wires and brackets by immersing them in ethanol solution and SEM (scanning electronmicroscope) evaluation confirmed the presence of the ZnO coating. The frictional forces were calculated between the wiresand brackets in four groups: group ZZ (coated wire and bracket), group OO (uncoated wire and bracket), group ZO (coatedwire and uncoated bracket) and group OZ (uncoated wire and coated bracket). Kolmogorov-Smirnov, Mann-Whitney andKruskal-Wallis tests were used for data analysis.Results. The frictional force in ZZ (3.07±0.4 N) was the highest (P <0.05), and OZ (2.18±0.5 N) had the lowest amount of friction (P <0.05) among the groups. There was no significant difference in frictional forces between the ZO and OO groups (2.65±0.2 and 2.70±0.2 N, respectively).Conclusion. Coating of porcelain bracket surfaces with ZnO nanoparticles can decrease friction in the sliding technique,and wire coating combined with bracket coating is not recommended due to its effect on friction.

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Nano sized ZSM-5 zeolite samples were synthesized successively from kaolin clay as alumina source having a large amount of quartz (39%) and silicic acid as silica source by hydrothermal treatment with NaOH in the presence of tetrapropylammonium hydroxide as a template. Then the effect of kaolin content, crystallization temperature and time on the size and crystallinity of the products were investigated. The prepared samples were characterized using XRD, SEM, EDS and FT-IR techniques. The results showed that the synthesized ZSM-5 zeolite samples were almost pure and their crystallization was almost complete. The average particle size, as determined by Debye-Scherrer equation, was in the range of 20-42 nm. Increasing kaolin content on crystal size was more effective than increase in crystallization temperature and time. Additional evidences for the nano sized ZSM-5 zeolite were the asymmetric stretch vibration band at 1225 cm -1 in the FT-IR spectra and TEM images. The scanning electron micrographs of the synthesized zeolites showed that they are spherical shape crystals.