Effect of activation and preactivation on the mechanical behavior and neutral position of stainless steel and beta-titanium T-loops

Comparison of stainless steel and titanium-molybdenum alloy closing loop archwires using numeric simulation model based on finite element method

INTRODUCTION

The objective of this study was to determine and compare the moment-to-force (Mc/F) ratio and the type of tooth movement generated in the anterior and posterior segments in orthodontic space closure with stainless steel and titanium-molybdenum alloy loop archwires.

METHODS

Three-dimensional model of the maxilla from which the first premolar was extracted, 18 × 25-mil slot stainless steel brackets, and 16 × 22-mil stainless steel and β titanium-molybdenum alloy (TMA) closing loop archwires with anterior gable bend of 15° and posterior gable bend of 25° were constructed. The archwires were engaged in the brackets, and 1-mm activations were carried out, which were repeated 5 times. The anterior and posterior segment Mc/F ratio and the type of tooth movement generated by the 2 wires were compared.

RESULTS

It was found that the Mc/F ratio for the anterior segment was approximately 5 mm, and for posterior teeth was approximately 10 mm for both stainless steel and TMA closing loop archwire. The anterior teeth exhibited controlled tipping, whereas the posterior teeth showed bodily tooth movement, which was in accordance with the Mc/F ratio that was obtained.

CONCLUSIONS

The Mc/F ratio and the type of tooth movement exhibited by stainless steel and TMA closing loop archwires were similar in both anterior and posterior segments.

Comparative evaluation of T-Loop with different amount of pre-activation curvatures in lingual orthodontics- A finite element study

Introduction

Three-dimensional analysis of the moment, force and M/F ratio generated at the anterior and posterior region of the T-loop in five different groups of pre-activation curvatures using the finite element method.

Materials and method

In this study, the geometric model of maxilla was constructed using a CBCT scan. The bracket system simulated was of the STb lingual bracket system from Ormco (0.18slot) with specified tip and torque values of all maxillary teeth and the arch wire used was 0.016″x 0.016″ TMA (Ormco) for fabrication of T-loop with dimensions of 6 ​× ​2 ​× ​7 ​mm. There were five different models generated with pre-activation of: 20°,30°,40°,50° and 60° in T-loop. The software used for the post-processing of the model was ANSYS Workbench 19.2.

Result

When the amount of pre-activation of T-loop increased there was an increase in the moment, force and M/F ratio in all the five groups in lingual biomechanics.

Conclusion

Although, the M/F ratio depicts the type of movement that will take place is uncontrolled tipping in all the five pre-activation groups, clinically we should give pre-activation ranging from 30° to 60° in T-loop in lingual orthodontics.