Friction between archwires and labial brackets has received considerable attention; however, information on the frictional behaviour of commercially available lingual brackets is limited. The aim of this study was to investigate the frictional resistance resulting from a combination of lingual orthodontic brackets (7th Generation, STb, Magic, and In-Ovation L) and stainless steel archwires at 0, 5, and 10 degrees of second-order angulation. Each bracket type (n = 30) was tested with three different sizes of archwires. Static and kinetic frictional forces were evaluated with a universal testing machine. Statistical analysis of the data was performed with non-parametric Kruskal-Wallis and Dunn's multiple comparison tests. All tested brackets showed higher frictional forces as the wire size and second-order angulation increased. The lowest friction was found with In-Ovation L brackets and 0.016 inch archwires at 0 degrees angulation, and the greatest friction with a combination of STb brackets and 0.017 × 0.025 inch archwires at 10 degrees angulation. For all combinations, Magic and In-Ovation L brackets showed lower frictional resistance when compared with 7th Generation and STb brackets. The slot width (occluso-gingival dimension) of the brackets, measured using the optics of a microhardness machine, showed that all brackets were oversized and that Magic brackets had the largest slot width. Surface roughness of the brackets investigated using atomic force microscopy and scanning electron microscopy, demonstrated that the 7th Generation brackets had the greatest surface roughness.
This article describes a series of experiments conducted to determine the effects of loading history and manufacturing techniques on mechanical behavior of high- density polyethylene (HDPE). The main reason for undertaking the research was to investigate multiple creep, multiple relaxation, and cyclic loading on uniaxial tension. The samples used for tensile tests were obtained from extruded pipe and compression-molded sheets. The stress—strain responses of both samples under uniaxial tensile were found to be independent of the loading history. It was observed that the compression-molded specimens exhibit greater deformation ratio than the extruded specimen. Understanding the deformation behavior under different loading can offer the designer of high-density polyethylene products reliable data relevant to practical applications.
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