Bulent Aydemir

Light Curing the Primer—Beneficial When Working in Problem Areas?

The purpose of this study was to investigate whether Transbond XT with MIP and Assure were affected by light curing the primers before contamination with blood or saliva. The study material consisted of 180 human premolars. The teeth were assigned into 12 groups of 15 specimens each. Metal brackets were bonded to each tooth under five different enamel surface conditions: dry, contaminated with blood or contaminated with saliva after primer application without light curing the primer, and contaminated with blood or contaminated with saliva after primer application with light curing the primer. The shear bond strengths of the two adhesive groups were not significantly different from each other within the same surface condition. There was no statistically significant difference between the groups bonded under dry conditions. On the other hand, curing the primer before adhesive application enhanced the bond strength in the contamination groups. Saliva and blood behaved similarly, showing higher bond strength values when the primer was light cured before contamination. However, they revealed bond strengths of different magnitudes because of the differences in the type and amount of inorganic and organic substances they contained. Under ideal conditions, light curing the primer did not introduce any advantages. However, curing the primer before contamination revealed higher bond strengths. To minimize the negative effect of contamination on bond strength, it would be appropriate for clinicians to light cure immediately after the application of the primer.

A comparative in vitro study of frictional resistance between lingual brackets and stainless steel archwires

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 Dunns 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.

The Effects of Loading History and Manufacturing Methods on the Mechanical Behavior of High-Density Polyethylene

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.

New Protective Polish Effects on Shear Bond Strength of Brackets

One of the solutions for the problem of white spot lesions has been the application of a polymer coating to the labial enamel surface. The aim of this study is to find out whether the liquid polish BisCover affects the bond strength of brackets bonded with a light-cured system (Transbond XT) and a no-mix system (Unite). Standard stainless steel premolar brackets were bonded to 100 permanent human premolars randomly divided into five equal groups. Two different enamel surface conditions were studied: dry and varnished with BisCover. For each enamel surface condition, two orthodontic adhesive systems were used: a light-cured system (Transbond XT) and a no-mix system (Unite). All teeth were conditioned with 37% phosphoric acid for 30 seconds, followed by thorough washing and drying. The teeth in groups 1 and 2 were bonded with Transbond XT and Unite, respectively. For groups 3, 4, and 5, a thin layer of BisCover was applied to the etched enamel with a brush and light cured for 15 seconds. In group 3, a thin layer of Transbond XT primer was applied, whereas in group 5, no additional primer was used on BisCover. In groups 3 and 5, the brackets were bonded with Transbond XT adhesive resin. Group 4 was bonded with no-mix Unite. Shear forces were applied to the samples by a Zwick Universal test machine, and bond strengths measured in megapascals. The results revealed that shear bond strengths of the groups did not differ significantly from each other.

Ni-625 Superalloy Foam Processed by Powder Space-Holder Technique

In this work, porous Ni-625 superalloys were produced by use of a water soluble pore forming agent prior to sintering. Carbamide particles were used as the space-holder materials. After mixing and compaction, the space-holder particles were extracted using warm water leaching over a range of temperatures. The porous green parts were subsequently thermally debinding to remove the paraffin wax under a pure Argon atmosphere, and subsequently sintered at high vacuum. The effects of volume fraction of space-holder particles on density, porosity, and elastic modulus were investigated. Microstructures were captured using optical and scanning electron microscopy. Pore size was quantified using image analysis software integral to the scanning electron microscopy. In addition, compression tests were conducted on the sintered samples.

Cyclic Behavior of High Density Polyethylene (HDPE)

This article presents the mechanical behavior of high density polyethylene (HDPE). Samples were prepared by extracting extruded HDPE pipe. Cyclic and strain rate jump behavior of HDPE were studied under uniaxial tensile loading conditions. The strain jump tests indicated that mechanical behavior of HDPE has deformation memory. Further, it was found that increasing cycle number on cyclic loading test increased strain accumulation amount and HDPE exhibited ratcheting behavior at on loading‐unloading‐reloading at constant stress level.