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.

Smart Spaces Spring

An innovative auxiliary spring design is presented to provide space creation in various clinical situations. Accompanied with a further innovative method of activation, it shall also limit the reciprocal movements of adjacent mesial teeth.

Stability of beta-titanium T-loop springs preactivated by gradual curvature

OBJECTIVE

Evaluate changes in the force system of T-Loop Springs (TLS) preactivated by curvature, due to stress relaxation.

METHODS

Ninety TLSs measuring 6 x 10 mm, produced out with 0.017 x 0.025-in TMA® wire and preactived by gradual curvature, were randomly distributed into nine groups according to time point of evaluation. Group 1 was tested immediately after spring preactivation and stress relief, by trial activation. The other eight groups were tested after 24, 48 and 72 hours, 1, 2, 4, 8 and 12 weeks, respectively. Using a moment transducer coupled to a digital extensometer indicator adapted to a universal testing machine, the amount of horizontal force, moment and moment-to-force ratios were recorded at every 0.5 mm of deactivation from 5 mm of the initial activation, in an interbracket distance of 23 mm.

RESULTS

The horizontal forces decreased gradually among the groups (p< 0.001) and the moments showed a significant and slow decrease over time among the groups (p< 0.001). All groups produced similar M/F ratios (p= 0.532), with no influence of time.

CONCLUSIONS

The TLSs preactivated by curvature suffered a gradual deformation over time, which affected the force system, specifically the moments, which affected the horizontal forces produced.

The T-loop in details

INTRODUCTION

The T-loop as designed by Burstone is a space closure spring used in the rational application of orthodontic biomechanics. Despite the diversity of studies, there is still no consensus on the optimal parametric characteristics for its conformation.

OBJECTIVE

This study aimed at reviewing the literature on the force systems released by different conformations of the T-loop, according to the type of anchorage and the main characteristics and factors that influence them.

RESULTS

Comparing the studies, the need for standardization was perceived in the methodology to shape the loops, regarding the variables that influence the force system. Most of the experimental studies with this loop do not report the vertical movement, nor the steps and angles that occur in the brackets. Clinical studies have obtained more variable results in relation to vertical acting forces, considering the influence of chewing.

CONCLUSION

There is great potential for future studies with this type of loop, especially using nickel-titanium alloys, in order to achieve a pure translational movement without friction, with optimal and constant levels of force.

Differences in the force system delivered by different beta-titanium wires in elaborate designs

Objective:

Evaluation of the force system produced by four brands of b-Ti wires bent into an elaborate design.

Methods:

A total of 40 T-loop springs (TLS) hand-bent from 0.017 x 0.025-in b-Ti were randomly divided into four groups according to wire brand: TMA^TM(G1), BETA FLEXY^TM (G2), BETA III WIRE^TM (G3) and BETA CNA^TM (G4). Forces and moments were recorded by a moment transducer, coupled to a digital extensometer indicator adapted to a testing machine, every 0.5 mm of deactivation from 5 mm of the initial activation. The moment-to-force (MF) ratio, the overlapping of the vertical extensions of the TLSs and the load-deflection (LD) ratio were also calculated. To complement the results, the Young's module (YM) of each wire was determined by the slope of the load-deflection graph of a tensile test. The surface chemical composition was also evaluated by an energy dispersive X-ray fluorescence spectrometer.

Results:

All groups, except for G2, produced similar force levels initially. G3 produced the highest LD rates and G1 and G4 had similar amounts of overlap of the vertical extensions of the TLSs in "neutral position". G1 and G3 delivered the highest levels of moments, and G2 and G3 produced the highest MF ratios. b-Ti wires from G3 produced the highest YM and all groups showed similar composition, except for G2.

Conclusion:

The four beta-titanium wires analyzed produced different force systems when used in a more elaborate design due to the fact that each wire responds differently to bends.

Segmented arch or continuous arch technique? A rational approach

This study aims at revising the biomechanical principles of the segmented archwire technique as well as describing the clinical conditions in which the rational use of scientific biomechanics is essential to optimize orthodontic treatment and reduce the side effects produced by the straight wire technique.

Determination of the force systems produced by different configurations of tear drop orthodontic loops

OBJECTIVE

To determine the mechanical characteristics of teardrop loop with and without helix fabricated using different metal alloy compositions (stainless steel and beta-titanium), submitted to different intensities of bends preactivation (0° and 40°), and with different cross-sectional dimension of the wire used to build these loops (0.017 x 0.025-in and 0.019 x 0.025-in).

METHODS

Eighty loops used to close spaces were submitted to mechanical tests. The magnitudes of horizontal force, the moment/force ratio, and the load/deflection ratio produced by the specimens were quantified. Loops were submitted to a total activation of 5.0 mm and the values were registered for each 1.0 mm of activation. For statistic data analysis, a analysis of variance was performed and a Tukey's Multiple Comparison test was used as supplement, considering a 5% level of significance.

RESULTS

In general, teardrop loops with helix produced lower magnitudes of horizontal force and load/deflection ratio, and higher moment/force ratio than teardrop loops without helix. Among all analyzed variables, metal alloy composition presented greater influence in the horizontal force and in the load/deflection ratio. The moment/force ratio showed to be more influenced by the preactivation of loops for space closure.

Force system evaluation of symmetrical beta-titanium T-loop springs preactivated by curvature and concentrated bends

INTRODUCTION

The objective of this research was to compare the effect of preactivation on the force system of beta-titanium T-loop springs (TLSs).

METHODS

Twenty TLSs with dimensions of 6 × 10 mm, of 0.017 × 0.025-in beta-titanium alloy, were randomly divided into 2 groups according to their preactivation. By using a moment transducer coupled to a digital extensometer indicator adapted to a testing machine, the amounts of horizontal force and moment produced were recorded at every 0.5 mm of deactivation from 5 mm of the initial activation in an interbracket distance of 23 mm. The moment-to-force ratio, the "neutral position" and the load-deflection ratio were also calculated.

RESULTS

TLSs preactivated by curvature delivered horizontal forces significantly lower than those preactivated by concentrated bends. No differences were found in relation to the moments produced throughout the deactivation of both groups. The moment-to-force ratios were systematically higher on the TLSs preactivated by curvature than those preactivated by concentrated bends, except on 5 mm of activation. Significant differences were found in the load-deflection rates and "neutral position."

CONCLUSIONS

The TLSs preactivated by curvature delivered lower horizontal forces and higher moment-to-force and load-deflection ratios than did those preactivated by concentrated bends.

Effects of stress relaxation in beta-titanium orthodontic loops

INTRODUCTION

This study evaluates the changes in the force system of the beta-titanium T-loop spring (TLS) caused by stress relaxation.

METHODS

Ninety TLSs with dimensions of 6 × 10 mm, made of 0.017 × 0.025-in beta-titanium alloy and preactivated by concentrated bends, were randomly distributed into 9 groups according to the time point of evaluation. Group 1 was tested immediately after spring preactivation and stress relief by trial activation. The other 8 groups were tested after 24, 48, and 72 hours, and 1, 2, 4, 8, and 12 weeks. By using a moment transducer coupled to a digital extensometer indicator adapted to a universal testing machine, the amounts of horizontal forces and moments and the moment-to-force ratios were recorded at every 0.5 mm of deactivation from 5 mm of the initial activation in an interbracket distance of 23 mm.

RESULTS

The horizontal forces and moments were higher (P <0.001) for group 1 compared with the other 8 groups, which were not different among themselves. All groups produced similar moment-to-force ratios (P = 0.600), with no influence of time.

CONCLUSIONS

The TLSs preactivated by concentrated bends had progressive load decreases over time, and this effect is critical in the first 24 hours.

A comparison of space closure rates between preactivated nickel-titanium and titanium-molybdenum alloy T-loops: a randomized controlled clinical trial

The purpose of this study was to conduct a prospective randomized controlled clinical trial to evaluate the rate of space closure and tooth angulation during maxillary canine retraction using preactivated T-loops made from titanium-molybdenum alloy (TMA) and nickel-titanium (NiTi). Twelve patients (six males and six females) aged between 13 and 20 years who had upper premolar extractions were included, and each acted as their own control, with a NiTi T-loop allocated to one quadrant and TMA to the other using a split mouth block randomization design. The loops were activated 3 mm at each visit to deliver a load of approximately 150 g to the upper canine teeth. Maxillary dental casts, taken at the first and each subsequent monthly visit, were used to evaluate changes in extraction space and canine angulation. All used T-loops were compared with unused loops in order to assess distortion. Mixed model statistical analysis was used to adjust for confounding variables. The mean rate of canine retraction using preactivated NiTi and TMA T-loops was 0.91 mm/month (±0.46) and 0.87 mm/month (±0.34), respectively. The canine tipping rates were 0.71 degrees/month (±2.34) for NiTi and 1.15 degrees/month (±2.86) for TMA. Both the rate of space closure and the tipping were not significantly different between the two wire types. The average percentage distortion of the TMA T-loop was 10 times greater than that of the NiTi loops when all other variables were matched. There was no difference in the rate of space closure or tooth angulation between preactivated TMA or NiTi T-loops when used to retract upper canines. The NiTi loops possessed a greater ability to retain and return to their original shapes following cyclical activation.