Interbracket Distance Research Articles

Assessment of the Force-Deflection Behavior of Aged NiTi Archwires in Various Inter-Bracket Distance Configurations

The aim of the study was to determine the force-deflection behavior of aged nickel-titanium (NiTi) archwires when subjected to bending within a bracket model featuring different inter-bracket distances. The flexural behavior of commercial 0.016 × 0.022-inch NiTi archwires was modified by subjecting them to different ageing temperatures. The archwire with the lowest unloading force during bending in a three-point bending arrangement was chosen for force-deflection evaluation at various inter-bracket distances. The findings indicate that subjecting the commercial as-received NiTi archwires to an ageing treatment at a temperature of 490 °C effectively decreased the magnitude of the unloading force from 2.0 N to 1.3 N. It was also discovered that NiTi archwires displayed unloading force in the form of a slope over the deflection course when narrow inter bracket distances of 7.0 mm and 7.5 mm were used. The force slope exhibited a significant decrease and approached a nearly constant force trend when the inter-bracket distance was increased to 8.5 mm and 9.0 mm. The unloading force of 490 °C aged NiTi archwires exhibited a progressive increase from 1.7 N to 3.4 N as the spacing between the brackets was altered from 7.0 mm to 9.0 mm. The ageing treatment approach might be useful for reducing the bending force released by commercial rectangular NiTi archwires at different inter-bracket distance settings.

SPACE CLOSURE EFFECT ON FORCE SYSTEM IN THE SEGMENTED ARCH: AN EXPERIMENTAL-NUMERICAL STUDY

Objective: To perform an experimental-numerical analysis to study the influence of the interbracket distance (IBD) on the spring’s mechanical behavior and on the resulting force system during space closure in the segmented arch technique (SAT). Material and Methods: Twenty delta springs (DSs) made of beta-titanium alloy, [Formula: see text] inch, were tested on a platform transducer. A Young’s modulus ([Formula: see text] of 69 GPa ([Formula: see text] psi) and Yield’s strength ([Formula: see text] of 1240 MPa ([Formula: see text] psi) were used. The springs were activated considering different IBDs. The spring was modeled in autodesk Inventor software and its behavior was simulated using the finite element (FE) code Ansys Workbench. Results: The ANOVA showed a significant difference in the studied variables with a reliability of over 95% (only for the activation variable there was an effect upon the horizontal forces (Fx). The Tukey HSD and the Games–Howell post hoc multiple comparisons tests were applied to identify differences between the treatments for heterogeneous variances. Conclusions: The IBDs do not significantly affect the force system during space closure, even though there was an increase in the Mz/Fx ratio as spring deactivates. Activation can cause a statistically significant effect on the force system even though the force showed safe levels. At 4[Formula: see text]mm activation (19[Formula: see text]mm IBD), the spring wire starts yielding, i.e. plastic deformation occurs near the anterior attachment due to the shorter IBD.

Deflection of tandem archwire in a specific self-ligating metal bracket system: an in vitro study.

The aim of this study was to quantify the force exerted by tandem archwires in a specific system of passive self-ligating bracket. Forty-eight thermo-activated nickel-titanium orthodontic archwires were separated into four groups (n = 12): G1 - two .014" + .014" round archwires; G2 - two .014" + .016" round archwires; G3 - .014" x .025" rectangular archwire; and. G4 - .016" x .022" rectangular archwire. Brackets were fixed onto teeth 1.5 to 2.5 using a device that represented the upper teeth, maintaining an interbracket distance of 6.0 mm. The deflection tests were performed using the structure representative of tooth 1.1 as support on the Instron testing machine at a speed of 2.0 mm/min. The archwires were evaluated at deflections of 0.5 mm, 1.0 mm, and 1.5 mm. The data were analyzed by a generalized linear model, considering values at different deflections as repeated measurements in the same experimental unit (α = 0.5%). At 0.5 mm, higher forces were observed in G2 and G3, which did not differ significantly (p > 0.05). The lowest force was observed in G4 (p < 0.05). At 1.0 mm and 1.5 mm, the highest force was observed in G3, followed by G4 and G2 (p < 0.05). The lowest force was observed in G1 (p < 0.05). In general, tandem archwires (same or different calibers) in a specific passive self-ligating bracket exerted lower force when compared with rectangular archwires.

Development of Regression Models for the Prediction of NiTi Archwire Forces in an Orthodontic Bracket System Using Response Surface Methodology

Superelastic NiTi archwire is extensively employed in the early stage of orthodontic therapy due to its capacity to transmit constant and light force to the tooth. The archwire force prediction for orthodontic treatment planning becomes a challenging process as the generated friction at the wire-bracket interface modifies the force exerted by the NiTi archwire. If plotted, the typical force plateau behavior of the superelastic NiTi archwire now gives way to a slope. This study established regression models for estimating the magnitude of forces released by NiTi archwire when bent at various settings in an orthodontic bracket system. Four bending settings parameters were considered: archwire geometry, inter bracket distance, the magnitude of archwire deflection, and testing temperature. The relationships between the settings and the wire forces were investigated using a response surface methodology approach based on data obtained from bending simulation. The magnitude and slope of the unloading force of superelastic NiTi archwire decrease gradually as the amount of wire deflection and inter-bracket distance increase, respectively. NiTi archwires with a diameter of 0.016 inches are best used in the early stages of orthodontic therapy because of their lower unloading forces of 0.57 N to 1.71 N and lower force slope values of 0.13 N/mm to 0.72 N/mm. The developed regression models have strong R-squared values for the loading force, unloading force, and force slope of 0.996, 0.9830, and 0.9748, respectively, and may thus be used to aid the orthodontist in forecasting the amount of force being exerted on a tooth in various malocclusion conditions.

Comparative investigation of fully customized lingual bracket systems and conventional labial appliances: Analysis of forces/moments and final tooth positions

The assessment of forces and moments generated by fully customized lingual appliances and their effectiveness in tooth movement were compared with conventional labial bracket systems, applied to a specific malocclusion model. Two fully customized lingual appliances (Incognito [3M Unitek, Monrovia, Calif] and WiN [DW Lingual Systems, Bad Essen, Germany]) and 2 labial bracket systems (Discovery classic and Discovery smart [Dentaurum, Ispringen, Germany]) were examined with nickel-titanium wires of different cross-sections (0.012, 0.014, 0.016, and 0.016 × 0.022-in) and 3 tooth types (canine, lateral incisor, and second premolar). Simulated movement was performed with a wire replacement as soon as forces or moments were no longer effective. Lingual and labial appliances showed statistically significant differences in initial forces and moments when tested with the same cross-section wires. Statistically significant differences between the 2 lingual bracket systems were also registered. Both lingual appliances rotated the premolar less than the conventional labial appliances. In areas of smaller lingual interbracket distance and higher lingual slot misalignment, the tested lingual multibracket appliances showed higher forces than the labial appliances. The force difference was particularly prominent with vertically oriented lingual slots and rectangular wires. The tested lingual appliances presented difficulties in rotating the premolar.

Influence of inter-bracket distance on load deflection characteristics of nickel-titanium wires

Aim: Aim of this study was to compare and evaluate load deflection characteristic of NiTi wires of different cross-section between labial and lingual straight wire system in aligned and crowded condition. Materials &amp; Methods: The study was divided into two parts one with the aligned teeth and in other part typodont set was manipulated to simulate the crowded arch. Crowding was created in the anterior region by displacing one central incisor and one lateral incisor 2 mm palataly and canine were rotated in mesio-buccal direction. Typodont was sent to laboratory for lingual setup and CAD-CAM based Avant grade laser sintered 3D lingual brackets were and bonded using Cyanoacrylate by the laboratory. A modified three point bending test simulating the clinical conditions was carried out to investigate load deflection characteristics of Cu-NiTi arch-wires using Instron Universal Testing Machine. Results: Shapiro-wilk test and Kolmogorov-Smirnov test were used to check the normality of the sample and values. Intergroup comparison of LDR of wires between labial and lingual group in aligned and crowded condition showed that LDR of wires in the lingual bracket system was significantly higher as compared to labial bracket system.

In vitro comparison of the mechanical behaviour of archwires after computer-assisted and conventional bracket positioning protocols

The mechanical properties of orthodontic archwires can be defined using experimental setups incorporating brackets that provide conditions closer to those encountered in vivo. We aimed to compare a methodology based on computer-aided design with the gold standard protocol, performed when brackets are engaged to a full-size archwire to test the behaviour of wires in this condition. Three models simulating a dental arch with an orthodontic fixed appliance (0.018-inch aesthetic conventional brackets) were designed. The brackets were positioned with a stainless-steel full-size wire on the first two models, with different interbracket distances. The setup 3, based on a computer-assisted design, allowed individualized placement of each bracket. Mean forces recorded and standard deviation were compared for a 0.016×0.022-inch copper-nickel-titanium wire deflected until 2mm. The inter-bracelet distances do not cause a statistical difference in the average maximum force recorded (12.6N and 11.4N; P=0.081) whereas the behaviour of the wires is affected. With setup 3, the recorded efforts (mean value: 8N) are statistically lower than with setup 1 and 2 respectively (P=0.018; P=0.012). An individualization of the housings by CAD-CAM dedicated to each bracket optimizes their placement. In our test conditions, the mechanical behaviour of the wires is more influenced by the positioning methods of the brackets than by the value of the interbracket distance. In perspective, our innovative methodology can be extended to other types of brackets.

Torque Comparison Between Two Passive Self-Ligating Brackets with Respect to Interbracket Wire Dimensions and Types: A Finite Element Analysis

Objective: This study aimed to analyze the expression of torque between 2 passive self-ligating brackets by simulating different clinical situations using finite element analysis. Material and Methods: Two passive self-ligating brackets, that is, Damon Q (Ormco, Glendora, California) and Smart Clip (3M Unitek, Monrovia, California), were 3D modeled using micro-computed tomography. ANSYS V14.5 software was used for analysis. Archwire and bracket interactions were simulated to measure torque expression by changing wire alloys (stainless steel [SS] and titanium molybdenum [TMA]) and interbracket dimensions. Results: Damon Q brackets generated higher torque values compared to Smart Clip brackets with both SS and TMA wires. Damon Q brackets generated the highest torquing moment of 25.72 Nmm and 7.45 Nmm, while Smart Clip brackets generated 22.25 Nmm and 7.31 Nmm with 0.019 × 0.025″ SS and TMA wires, respectively, at an interbracket distance of 12 mm. Torquing moments decreased for Damon Q and Smart Clip brackets when wire length increased from 12 mm to 16 mm. Conclusion: Damon Q with 0.019 × 0.025″wires exhibited superior torquing characteristics as compared to Smart Clip brackets with similar archwires.

Comparison of multiforce nickel-titanium wires to multistrand wires without force zones in bending and torque measurements.

The aim was to compare rectangular multiforce nickel-titanium (NiTi) wires to rectangular wires with only one force zone. Both types of wires are primarily intended for use during the levelling phase of orthodontic treatment. Thus, basic mechanical properties were examined by means of athree-point bending test. Torque expression, which is dependent on both wire parameters and interslot distances, was analyzed using the Orthodontic Measurement and Simulation System (OMSS). Four multizone products were tested: DuoForce™ (Forestadent, Pforzheim, Germany), TriTanium™ (American Orthodontics, Sheboygan, WI, USA), Triple Force™ (ODS, Kisdorf, Germany), Bio-Active™ (GC, Breckerfeld, Germany), and two multistrand products without force zones: anine-strand NiTi, TurboWire™ (Ormco, Orange, CA, USA) and an eight-strand stainless steel (SS) wire, Multibraid™ (GAC, Dentsply Sirona, York, PA, USA). All the wires had the dimension 0.40 mm × 0.56 mm (0.016 inch × 0.022 inch) except the nine-strand NiTi wire TurboWire™, which had a dimension of 0.43 mm × 0.65 mm (0.017 inch × 0.025 inch). Six different bracket systems in the 0.018 inch slot system were chosen: the conventional brackets discovery® and discovery® smart (Dentaurum, Ispringen, Germany), the active self-ligating brackets InOvation™ and InOvation™ mini (GAC, Dentsply Sirona, York, PA, USA) and the passive self-ligating brackets Carrière™ (ODS, Kisdorf, Germany) and BioPassive® (Forestadent, Pforzheim, Germany). The first set-up was athree-point bending test according to DIN EN ISO 15841. For the second experiment, the bracket products glued on amaxilla model were combined with the wire products. The torque moments arising during torqueing of the wires between +20° and -20° were measured in three positions: first incisor, canine and second bicuspid. Bending tests confirmed variation of the force corresponding to the force zones. The nine-strand NiTi wire TurboWireTM and the eight-strand SS wire Multibraid™ did not show any variation dependent on the tested area. Torque-moments generated by the multizone wires were higher compared to the braided wires. The nine-strand NiTi wire showed the lowest moments in spite of the higher dimension. As expected, increasing the interbracket distance reduced the torque moments. The tests verified the existence of multiple force zones in the NiTi wires for forces and moments, respectively. As the torque-moments arising from the multizone wires were rather high, it is not recommended to use these wires as afirst "leveling wire" in orthodontic treatment, especially in extremely crowded cases.

Experimental friction and deflection forces of orthodontic leveling archwires in three-bracket model experiments.

In vitro testing of archwires in amultibracket model may provide estimates of force-moment (F/M) systems applied to individual teeth in arealistic geometry. Such investigations have mostly been performed by continuous wire deflection, leading to frictional forces biasing the pure deflection forces. Aim of this study was to quantify this bias and the pure deflection forces for leveling archwires. Three nickel-titanium (NiTi) and two multistranded wires were tested in athree-bracket model simulating vertical movement of an upper incisor with atypical interbracket distance of 8 mm (intercenter). To determine pure deflection forces, the middle bracket was first leveled incrementally from its vertical malposition to neutral position with repeated wire insertion at each step (so-called "static leveling mode"). For comparison, forces at the middle bracket were also determined during dynamic leveling with or without ligation of the wire at the lateral brackets by either elastic, tight or loose steel ligatures. The dynamic mode resulted in significantly lower mean leveling forces for all the tested wires (ANOVA [analysis of variance], p < 0.01) compared to the static mode. Expressed in numbers, dynamic wire unloading resulted in mean force underestimation of 53 ± 9% (loose steel ligatures), 56 ± 11% (elastic ligatures) or 91 ± 29% (tight steel ligatures). Orthodontic tooth movement is quasi-static. This concerns the initial hyalinization phase in particular. Thus, especially static testing of archwires provides valid reference data for the peak forces exerted directly after clinical insertion of aleveling wire. In dynamic wire testing, significant underestimation of actual forces exerted on individual teeth may occur due to experimental friction, which might considerably differ from that occurring during clinical therapy. This aspect has to be taken into account in the interpretation of published stiffness values for orthodontic wires, and in the selection of the appropriate archwire for leveling of the present tooth malposition, respectively.

Effect of Interbracket Distance on Load-Deflection Property and Resistance to Sliding in Orthodontic Appliances

Introduction: Interbracket distance (IBD) plays a key role in load deflection and frictional resistance in the biomechanics of tooth movement. Aim: The aim of this study was to assess the influence of load deflection and friction between the bracket and archwire for a specific load on different bracket designs. Materials and Methods: IBD brackets ( n = 60), Sondhi Mini Uni-Twin brackets ( n = 60), low profile brackets ( n = 60), and Victory conventional brackets ( n = 60) were selected for the study. Load deflection was measured using a universal testing machine on 0.016″ nickel-titanium (NiTi) wire. A universal testing machine was used to measure the frictional resistance on 0.019″ × 0.025″ stainless steel wire. Results: The load deflection of 0.016″ NiTi wire was the highest in IBD followed by Sondhi Mini Uni-Twin, Sondhi conventional, and Victory conventional. Static friction and kinetic friction were the highest in Victory conventional brackets followed by low profile brackets, Sondhi Mini Uni-Twin, and IBD brackets. Conclusions: Load-deflection property will increase with increase in IBD, and frictional resistance will decrease with increase in IBD.

THE EFFECTS OF INTERBRACKET DISTANCE AND GABLE BENDS ON THE FORCE AND MOMENTS IN A SEGMENTED ARCH APPROACH: A NUMERICAL-EXPERIMENTAL STUDY

The present paper verified the effect of the interbracket distance on the force system developed by orthodontic retraction springs with two delta geometries measured during space closure when spaces between teeth are present. By using a platform transducer, five different interbracket distances were tested. Also the finite element method was applied to know the von Mises stress during spring activation/deactivation process. It was concluded that the interbracket distance and spring geometry variables have not caused significant influence on the force system resulting from activations, but activation has produced a statistical difference.

Effect of the vertical position of the canine on the frictional/orthodontic force ratio of Ni-Ti archwires during the levelling phase of orthodontic treatment.

This study investigated the effect of the vertical position of the canine on changes in the frictional/orthodontic (F/O) force ratio of nickel-titanium (Ni-Ti) archwires during the initial levelling phase of orthodontic treatment. Frictional and orthodontic forces were measured by using low-friction brackets and Ni-Ti archwires with three different cross-sectional sizes and force types. To simulate canine malocclusion (first premolar extraction case), the upper right canine was displaced gingivally by 1 to 3 mm and the inter-bracket distance between the upper right lateral incisor and second premolar was set at 15 mm or 20 mm. A three-point bending test was performed to measure the orthodontic force of each Ni-Ti archwire. Frictional forces were measured with a universal testing machine and dental arch models by pulling parallel to the end of the archwire at a crosshead speed of 0.5 mm/min. F/O force ratio was calculated and analysed statistically. At a displacement of 3 mm, few archwires had F/O force ratios of less than 1.0, at which orthodontic force overcame frictional force, thus ensuring extrusion of the canine. For effective tooth movement, orthodontists should use Ni-Ti archwires with an F/O force ratio of less than 1.0.

Comparison of stress distribution on bone and mini-implants during en-masse retraction of maxillary anterior teeth in labial and lingual orthodontics: A three-dimensional finite element analysis

INTRODUCTION: In fixed orthodontic treatment, space closure is one of the most challenging aspects. The common method of en-masse retraction in sliding mechanics is the use of the elastomeric chain and power arm. Recently, titanium mini-implants are used as absolute sources of orthodontic anchorage. Lingual and labial bracket placement influences the pattern of tooth movement, but the stress that occurs around the teeth, the mini-implants, and the surrounding bone can be accurately mapped using a three-dimensional (3D) finite element method. AIM: The aim of this study was to evaluate the stress distribution on bone and mini-implants during en-masse retraction of maxillary anterior teeth in labial and lingual orthodontics with the help of finite element analysis. MATERIALS AND METHODS: Following the standard protocol for 3D finite element models, two models were created for en-masse retraction of the six anterior teeth: one model using the labial technique with the mini-implant placed at a height of 5 mm from the alveolar crest bucally and the second model using the lingual technique with the mini-implant placed at a height of 5 mm from the gingival margin palatally, and 200 g of retraction forces was given using a elastomeric chain. RESULTS AND CONCLUSIONS: The Von Mises stresses in the bone and mini-implant were significantly higher in the lingual technique as compared to the labial technique. The variations in stress patterns in the bone and the mini-implant in the labial and lingual technique could be the result of difference in the inter-bracket distance, point of force application, and its location to the center of resistance of the dentition.

Effect of stress relaxation in two different preactivation methods of beta-titanium T-loops: bends vs. continuous curvature

ObjectiveAssess the changes in the force system of T-loop springs (TLSs) preactivated by bends and curvature, when secured in place with a constant strain over time. Materials and MethodsA total of 120 TLSs with dimensions 6 x 10 mm, produced out of 0.017 × 0.025-inch TMA, were randomly divided into two groups of 60 TLSs, each according to what preactivation was going to be used, concentrated bends or gradual curvature. Subgroup 1 was tested immediately and the remaining subgroups were tested after they were secured at 5-mm activation for different periods of time in an interbracket distance of 23 mm. Subgroups 2, 3, 4, 5, and 6 were kept activated for 24, 48, and 72 hours, 1 and 2 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 (MF) ratios were recorded. ResultsBoth groups showed a decrease in force levels over time (P < 0.001 and 0.005 for bend and curvature preactivation, respectively), but with different behaviors. The group preactivated by bends showed a reduction in moments over time (P < 0.001), whereas the group preactivated by curvature did not (P = 0.410). The MF ratio has not changed over time in either group. ConclusionsThe stress-relaxation effect is more evident on group preactivated by bends.

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

ABSTRACTObjective: 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.

Comparison of mechanical properties of three orthodontic wires between levelled and unlevelled brackets: An in vitro study

Background: The objective of this study was to compare the mechanical properties of three orthodontic wires between levelled and unlevelled bracket using a three-point bending test. Methods: Three groups of ten Nickel titanium, Betatitanium and CuNiTi wire segments (0.017 × 0.025-in. diameter) were used. Two brackets were bonded to an acrylic jig with a 10-mm interbracket distance. Deflection test was done in two scenarios, one with aligned brackets and other with 2-mm horizontal displacement of the brackets to simulate malaligned teeth. Forces of loading and unloading of the wires during both tests were compared by an analysis of variance (ANOVA) tests. Results: The difference of LDR between levelled and unlevelled brackets during loading in NiTi wire was 0.1 N, Beta-titanium wire 0.2 N and CuNiTi wire was 1.5 N. The difference of LDR between levelled and unlevelled brackets during unloading in NiTi wire was 0.2 N, Betatitanium wire was 0.3 N and CuNiTi wire is 0.5 N. Conclusions: The study showed some significant differences in forces generated during loading and unloading among the three different types of wires tested. During both the scenarios only CuNiTi wire showed significant difference. Betatitanium wire exhibited highest force followed by NiTi and CuNiTi. Keywords: NiTi, Beta-titanium, CuNiTi wires, Three-point bending test, Load deflection rate (LDR), Newtons (N)

Innovative design of closing loops producing an optimal force system applicable in the 0.022-in bracket slot system.

Most closing loops designed for producing higher moment-to-force (M/F) ratios require complex wire bending and are likely to cause hygiene problems and discomfort because of their complicated configurations. We aimed to develop a simple loop design that can produce optimal force and M/F ratio. A loop design that can generate a high M/F ratio and the ideal force level was investigated by varying the portion and length of the cross-sectional reduction of a teardrop loop and the loop position. The forces and moments acting on closing loops were calculated using structural analysis based on the tangent stiffness method. An M/F ratio of 9.3 (high enough to achieve controlled movement of the anterior teeth) and an optimal force level of approximately 250g of force can be generated by activation of a 10-mm-high teardrop loop whose cross-section of 0.019×0.025 or 0.021×0.025 in was reduced in thickness by 50% for a distance of 3mm from the apex, located between a quarter and a third of the interbracket distance from the canine bracket. The simple loop design that we developed delivers an optimal force and an M/F ratio for the retraction of anterior teeth, and is applicable in a 0.022-in slot system.

Effect of apical portion of T-, sloped L-, and reversed L-closing loops on their force systems.

To investigate the effect of the position of the apical portion of closing loops on the force system at both loop ends. T-loops were compared with backward-sloped L-loops (SL) and reversed L-loops (RL). SL-loops were directed toward the anterior side; RL-loops were directed toward the posterior side. Loop response to loop pulling was determined with finite element analysis at six positions of the apical loop portion for 12-mm interbracket distance and 8-mm loop length and height. Three-dimensional models of the closing loops were created using beam elements with the properties of stainless steel. Loop responses (horizontal load/deflection, vertical force, and moment-to-force ratio) at both loop ends were calculated as well as at 100 g and 200 g activation forces. T-, SL-, and RL-loops with the same position of the apical portion showed approximately the same force system at both loop ends. This behavior was found across the investigated range through which the loops were moved (interbracket center to posterior bracket). The center of the apical portion determined the force system of the closing loops regardless of the position of the loop legs. The centers of the apical portion of the T-, SL-, and RL-loops acted like V-bend positions.

Nickel titanium T-loop wire dimensions for en masse retraction.

To compare the force system produced by nickel-titanium T-loop springs made with wires of different dimensions. Thirty compound T-loop springs were divided into three groups according to the dimensions of the nickel-titanium wire used for its design: 0.016" × 0.022", 0.017" × 0.025", and 0.018" × 0.025". The loops were tested on the Orthodontic Force Tester machine at an interbracket distance of 23 mm and activated 9 mm. The force in the y-axis and the moment in the x-axis were registered while the calculated moment to force ratio was recorded at each .5 mm of deactivation. The data were analyzed by three analyses of variance of repeated measures to detect differences and interactions between deactivation and wire size on force, moment, and moment-force ratios (M/F). All groups had significantly different forces (P < .001). The 0.016" × 0.022" wire produced 1.78N of force while the 0.017" × 0.025" and the 0.018" × 0.025" produced 2.81 N and 3.25 N, respectively. The 0.016" × 0.022" wire produced lower moments (11.6 Nmm) than the 0.017" × 0.025" and 0.018" × 0.025" wires, which produced similar moments (13.9 Nmm and 14.4Nmm, respectively). The M/F produced was different for all groups; 0.016" × 0.022" T-loops produced 6.7 mm while the 0.017" × 0.025" and 0.018" × 0.025" T-loops produced 5.0 mm and 4.5 mm, respectively. An interaction was detected for all variables between deactivation and groups. The larger wires tested produced higher forces with slight increase on the moments, but the M/F produced by the 0.016" × 0.022" wire was the highest found.