Relation of forces and deflections during loading and unloading orthodontic nickel-titanium wires / "Relação entre força e deflexão na ativação e desativação de fios ortodônticos de níquel-titânio"

AUTOR(ES)
DATA DE PUBLICAÇÃO

2005

RESUMO

The purpose of this study was to evaluate the behaviour of force as function of loading and unloading orthodontic nickel-titanium wires. Three defferent brands (Forestadent, GAC and Morelli) were tested. Testing temperature were 32, 37 and 42 o C. Loading were up to 1, 2, 3 and 4mm deflection. Specimens consisted of a acrylic base where were fixed metallic cylinders simulating teeth. Over the teeth were fixed brackets to maintain arch wire in position. Tooth corresponding to central incisor was loosened and at the correspondig bráquete was applied the force in an Instron equipment, with temperature control. Head speed was 0.5mm/min. During loading and unloading forces were read every 0.10mm deflection and registered. The pair values of forces and deflections were also plotted as graphs. With 4mm maximum loading, 3 brands and 3 temperatures were obtained 36 experimental conditions and with 5 repetitions (n=5) were performed 180 tests. Graphs showed that there is no linearity between forces and deflection and with loading up to 1 and 2mm was not obtained the formation of superelasticity plateaus. But they were observed with 3 and 4mm deflections. From the graphs and registered numerical values for each specimen were selected special values to be analysed: 1) maximum loading force; 2/3) force decrease during unloading 0.20 and 0.70mm (the last only at 3 and 4mm activation); 4/5) exte nsions and forces at plateaus (only for 3 and 4mm activations); 6/7/8) extension until 50g force, since 0.80 and 1.80mm (respectively activation up to 1 and 2mm), or ends of plateau (3 and 4mm activation). In these conditions, the force at beginning unloading. Distance of origin at register 50g force; 9) permanent deformation at zero force. The main conclusions were: maximum loading forces increase with deflection and temperature increases, and brand Morelli presented the smallest force and GAC the greatest; the decrease of forces with unloading was as larger as activation force; only the activation until 3 and 4mm presented superelasticity plateaus, and was longer with 4mm activation, but it presented lower force at plateaus; in all tests was noted permanent deformation

ASSUNTO(S)

orthodontic wires superelasticidade nickel-titanium wires superelasticity fios de níquel-titânio fios ortodônticos

ACESSO AO ARTIGO

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