Evaluation of the Mechanical Performance of Modified Bull Retraction Loops

Objectives: This study aimed at evaluating the force systems generated by closed and open Bull loops when activated at 0 to 2.0mm and pre-activated at 20º, 30º and 40º, and investigate whether there were differences between the force systems generated by both loops at the same intensities of activation and pre-activation. Methods: Testing was performed of seventy two loops measuring 7.0mm in height and 3.5mm in external diameter, fabricated with.019” x .025” stainless steel (GAC). These loops were divided into two groups: group 1 comprised 36 closed loops and group 2 included 36 open loops. Both groups received pre-activations of 20º, 30º and 40º. An INSTRON universal testing machine was used, connected to a moment transducer and a digital for extensometer. Results: The results were analyzed by the three-way ANOVA, a complete factorial model, which revealed differences in the mean values of variables F, M, M/F and C/D in relation to the loop, pre-activation and activation; interactions between the three factors were also statistically significant (p<0.05). After observation of difference by the ANOVA test, the Tukey test was employed to identify which treatments were different from each other. Conclusions: Thus, it could be concluded that different pre-activations and activations yield statistically significant difference in the force and moment magnitudes, as well as different M/F and C/D ratios for loops in both groups 1 and 2; the force systems generated by the loops in group 1 presented higher means than those in group 2.