The Effect of Residence Time on the Tensile Properties of Superelastic and Thermal Activated Ni-Ti Orthodontic Wires

Since the 1980s, different devices based on superelastic alloys have been developed to fulfill orthodontic applications. Particularly in the last decades several researches have been carried out to evaluate the mechanical behavior of Ni-Ti alloys, including their tensile, torsion and fatigue properties. However, studies regarding the dependence of elastic properties on residence time of Ni-Ti wires in the oral cavity are scarce. Such approach is essential since metallic alloys are submitted to mechanical stresses during orthodontic treatment as well as pH and temperature fluctuations. The goal of the present contribution is to provide elastic stress-strain results to guide the orthodontic choice between martensitic thermal activated and austenitic superelastic Ni-Ti alloys. From the point of view of an orthodontist, the selection of appropriate materials and the correct maintenance of the orthodontic apparatus are essential needs during clinical treatment. The present work evaluated the elastic behavior of Ni-Ti alloy wires with diameters varying from 0.014 to 0.020 inches, submitted to hysteresis tensile tests with 8% strain. Tensile tests were performed after periods of use of 1, 2 and 3 months in the oral cavity of patients submitted to orthodontic treatment. The results from the hysteresis tests allowed to exam the strain range covered by isostress lines upon loading and unloading, as well as the residual strain after unloading for both superelastic and thermal activated Ni-Ti wires. Superelastic Ni-Ti wires exhibited higher load isostress values compared to thermal activated wires. It was found that such differences in the load isostress values can increase with increasing residence time.

Dimensão educativa do trabalho: estudo de caso da associação de bordadeiras do Seridó ABS- Caicó/ Rio Grande do Norte

This current work s contains issues about the educative dimension of work and its organization s process and managing for it own professionals. It aims to understand how the skills and pedagogic process, in a educative praxis perspective. Are based in a new culture of work of education process an work managing by workers in Handcraft Association of Serido/ Caicó/ RN. It uses as a methodologic-theoric reference cases s study approach, selecting the procedures of part extructure interview. It was done with six embroidereses from the Handcraft Association. The research shows that the educative process of learning and knowledges construction, in the work and by the work. Those processes develop in exchange experiences net in a friendly economic environment and raise elements of a work culture personal that work there. The embroidereses learn how to embroid doing the job and this learning, a lot of times, is influenced by the life conditions, residence local and infantile work in the country area and the living to the urban area, particularly to Caicó. The knowledge relation between them is the matter fact in the embroider learning process that means a social relation based on the knowledge differences between their position in its structure involving the work division, that each handcraft maker knows every part of the embroider, type of work or machine type, step by step until the work is done. It involves decision, execution and machine movements repetition, the focus are the categories that fit in current flexible financial issue. They schedule the work at home so they have time to do other stuff. Most part of the production currently is done to obey de a certain request that aims as production target, being a homework. Another important issue is the embroider work time: time and experience that is within in the professional life and its knowledge representation of job/profession. This time is got as a acquisition process of certain a work dominion and self knowing; time added to changes that were being there practicing from the new characteristics in the furniture, clothes and towels that are in the introduction communicative and its effect. In this way this work include articulations process among skills, educative process and handcraft work organization that allowed the interpretation and finish, that are related to the case study and its developments: handcraft embroidered considered as a profession, money source not conventional where is not work available and a temporary activity while studyng, homework and flexible work

The Effect of Residence Time on the Tensile Properties of Superelastic and Thermal Activated Ni-Ti Orthodontic Wires

Since the 1980s, different devices based on superelastic alloys have been developed to fulfill orthodontic applications. Particularly in the last decades several researches have been carried out to evaluate the mechanical behavior of Ni-Ti alloys, including their tensile, torsion and fatigue properties. However, studies regarding the dependence of elastic properties on residence time of Ni-Ti wires in the oral cavity are scarce. Such approach is essential since metallic alloys are submitted to mechanical stresses during orthodontic treatment as well as pH and temperature fluctuations. The goal of the present contribution is to provide elastic stress-strain results to guide the orthodontic choice between martensitic thermal activated and austenitic superelastic Ni-Ti alloys. From the point of view of an orthodontist, the selection of appropriate materials and the correct maintenance of the orthodontic apparatus are essential needs during clinical treatment. The present work evaluated the elastic behavior of Ni-Ti alloy wires with diameters varying from 0.014 to 0.020 inches, submitted to hysteresis tensile tests with 8% strain. Tensile tests were performed after periods of use of 1, 2 and 3 months in the oral cavity of patients submitted to orthodontic treatment. The results from the hysteresis tests allowed to exam the strain range covered by isostress lines upon loading and unloading, as well as the residual strain after unloading for both superelastic and thermal activated Ni-Ti wires. Superelastic Ni-Ti wires exhibited higher load isostress values compared to thermal activated wires. It was found that such differences in the load isostress values can increase with increasing residence time.