comparison of mechanical properties between three different types of t-loop

statement of problem: t-loop is one of the most popular closing loops in orthodontic profession. however its activation is in the contrary to bouschinger effect theory, since the formed bends would be opened during activation. the purpose of this study was to add a helix in a way to be more respondent to the bouschinger effect theory. objectives: to compare the load deflection, maximal elastic load and range between three different types of t-loop. materials and methods: 5 sample of each 3 different designs of t-loop (group 1: original t-loop, group 2: t-loop with the two inner helices, group 3: t-loop with the two helices constructed outside the horizontal part) had been tested with universal testing machine (instron). the load –deflection curves was plotted and the mechanical properties (load deflection, maximal elastic load and range) were measured. one way anova was used to identify statistical differences between designs. results: the mean value of maximal elastic load in group 1 (6.02±0.27) was significantly higher than group 2 (5.16±0.46) and in group 2 were significantly higher than group3 (4.35±0.25) ( p <0.001). a significantly higher load deflection was reported in group 1 (0.73±0.36) in comparison to group2 (0.56±0.74) and group 3(0.56±0.69) ( p =0.002), with no significant difference between two latest groups ( p =0.999). the mean range in group 3 (4.15±0.10) was significantly lower than group 1(5.43±0.13) and group 2 (5.59±0.15) ( p =<0.001) with no significant difference between group 1 and 2 ( p =0.149). conclusions: the results revealed that increasing length of t-loop with helices will decrease load deflection rate the place and design of helices might not be a crucial factor. the new design of t-loop with helices relevant to bouschinger effect theory needs a further survey regarding their position.