Torque Expression Research Articles

Torque expression in self-ligating orthodontic brackets and conventionally ligated brackets: A systematic review.

BackgroundTo evaluate the torque expression of self ligating (SL) orthodontic brackets and conventionally ligated brackets and the torque expression in active and passive SL brackets.Material and MethodsOur systematic search included MEDLINE, EMBASE, CINAHL, PsychINFO, Scopus, and key journals and review articles; the date of the last search was April 4th 2016. We graded the methodological quality of the studies by means of the Quality Assessment Tool for Quantitative Studies, developed for the Effective Public Health Practice Project (EPHPP).ResultsIn total, 87 studies were identified for screening, and 9 studies were eligible. The quality assessment rated one of the study as being of strong quality, 7 (77.78%) of these studies as being of moderate quality. Three out of 7 studies which compared SL and conventionally ligated brackets showed, conventionally ligated brackets with highest torque expression compared to SL brackets. Badawi showed active SL brackets with highest torque expression compared to passive SL brackets. Major and Brauchli showed no significant differences in torque expression of active and passive SL brackets.ConclusionsConventionally ligated brackets presented with highest torque expression compared to SL brackets. Minor difference was recorded in a torque expression of active and passive SL brackets. Key words:Systematic review, self ligation, torque expression, conventional ligation.

Torque differences according to tooth morphology and bracket placement: a finite element study.

Torque of the maxillary incisors is essential in esthetics and proper occlusion, while torque expression is influenced by many factors. The aim of this finite element study was to assess the relative effect of tooth morphology, bracket prescription, and bracket positioning on tooth displacement and developed stresses/strains after torque application. A three-dimensional upper right central incisor with its periodontal ligament (PDL) and alveolus was modelled. The tooth varied in the crown-root angle (CRA) between 156°, 170°, and 184°. An 0.018-inch slot discovery® (Dentaurum, Ispringen, Germany) bracket with a rectangular 0.018 × 0.025-inch β-titanium wire was modelled. Bracket torque prescription varied between 0°, 12°, and 22°, with bracket placement at the centre of the middle, gingival or incisal third of the crown. A total of 27 models were generated and a buccal root torque of 30° was applied. Afterwards, crown and apex displacement, strains in the PDL, and stresses in the bracket were calculated and analysed statistically. The palatal crown displacement was significantly affected by bracket positioning (up to 94 per cent), while the buccal apex displacement was significantly affected by bracket prescription (up to 42 per cent) and bracket positioning (up to 23 per cent). Strains in the PDL were affected mainly by CRA (up to 54 per cent), followed by bracket positioning (up to 45 per cent). Finally, bracket prescription considerably affected the stresses in the bracket (up to 144 per cent). These in silico results need to be validated in vivo before they can be clinically extrapolated. Tooth anatomy and the characteristics of the orthodontic appliance should be considered during torque application.

Applications of cone-beam computed tomography to assess the effects of labial crownmorphologies and collum angles ontorquefor maxillary anterior teeth.

Currently, cone-beam computed tomography (CBCT) has been widely used because of its capacity to evaluate the anatomic structures of the maxilla, mandible, and teeth in 3 dimensions. However, articles about the use of CBCT to evaluate the relationships between the morphology of individual teeth and torque expression remain rare. In this study, we aimed to determine the influence of labial crown morphologies and collum angles on torque for maxillary anterior teeth using CBCT. A total of 206 extracted maxillary anterior teeth were selected to establish scanning models using dental wax, and they were scanned by CBCT. Three-dimensionally reconstructed images and median sagittal sections of the teeth were digitized and analyzed with AutoCAD software (Autodesk, San Rafael, Calif). The angle α, formed by the intersection of the tangent at a certain vertical height on the labial surface from the incisal edge with the crown long axis, and the collum angle, were measured. The variations in angle α at different heights from the incisal edge for the same type of tooth were statistically significantly different (P<0.001). Moreover, the variations betweencollum angles and 0° for any type of maxillary anterior tooth were statistically significant (P<0.01). This study suggested that there are great differences in labial crown morphologies and collum angles for maxillary anterior teeth between persons, indicating that the morphologies of these teeth do play important roles in torque variations.

Comparison of Torquing Ability of 0.019” × 0.025” Nickel Titanium and Fiber Composite Archwires -A Cone Beam Computed Tomography Study

Background Increase in the number of adult patients seeking orthodontic treatment for aesthetics, demand for a more aesthetic orthodontic appliance has become inevitable. Objectives This prospective study was undertaken to evaluate torque expression of 0.019” × 0.025” fiber composite wire and 0.019” × 0.025” NiTi wire in a similar prescription bracket systems (MBT, 0.022” slot) using CBCT. Methods Twenty arches each (ten maxillary and ten mandibular), of 15 - 25 year old patients, were bonded with metal brackets and ceramic brackets having MBT prescription and 0.022”slot. Two CBCT images were recorded at T0 and Tx. T0 point represented the stage of transition from a 0.017” × 0.025” NiTi wire to a 0.019” × 0.025” fiber composite or NiTi archwire. The Tx time point represented the end of treatment phase using 0.019” × 0.025” dimension wire, i.e. after 3 months of T0 scan. Results The mean angulation change from T0 to Tx in fiber composite wire group and NiTi wire group was tested using Wilcoxon signed rank test and showed that the difference was statistically non-significant (P > 0.05). Conclusions It was concluded that fiber reinforced composite wires were comparable to NiTi wires in their ability to deliver consistent forces and bring about comparable torque in individual teeth.

Friction between Archwire of Different Sizes, Cross Section, Alloy and Brackets Ligated with Different Brands of Low Friction Elastic Ligatures- An Invitro Study.

Friction in orthodontic treatment does exist and is thought to reduce the efficiency of orthodontic appliances during sliding mechanics. During sliding mechanics, a friction force is produced at the bracket archwire-ligature unit which tends to counteract the applied force and in turn resists the desired movement. The aim of this invitro study was to determine the friction between archwire of different sizes, cross section, alloy and brackets ligated with different brands of low friction elastic ligatures. An 0.022-in slot, 10 stainless steel brackets and various orthodontic archwires which were ligated with low-friction ligatures and subjected to evaluate frictional resistance i.e. static friction and dynamic friction. The archwires of 0.014″ and 0.016″ nickel titanium (NiTi), 0.016 × 0.022″ stainless steel (SS), 0.017 × 0.025″ NiTi, 0.017 × 0.025″ SS, 0.017 × 0.025″ titanium molybdenum alloy (TMA), 0.019 × 0.025″ SS were used. Each bracket/archwire combination was evaluated 10 times at room temperature of 27 ± 2°C. The study groups included Group I of conventional round shape module with reduced friction coating i.e. super slick and synergy and Group II contained figure of "8" shape module i.e. Octavia ties and Slide ligature. The mean static friction force and dynamic friction force for all 7 types of wires was lower in Group II (C, D) combined compared to Group I (A, B) and the difference was statistically very highly significant (p<0.001). Super slick and synergy can be used in the initial and final phase of treatment when full engagement of archwire in the bracket slot is necessary for proper tip and torque expression. Slide and Octavia ties modules can be used in the premolar brackets during en mass retraction when using friction mechanics.

A New Analytical Torque Formula for Axial Field Permanent Magnets Coupling

In this paper, we present a simple and accurate analytical expression to compute the torque of axial-field magnetic couplings. The torque expression is obtained by solving the three-dimensional (3-D) Maxwell equations by the method of separation of variables. Here, we adopt the assumption of linearization at the mean radius, the problem is then solved in 3-D Cartesian coordinate (we neglect the curvature effects). To show the accuracy of the torque formula, the results are compared with those obtained from 3-D finite-element simulations and from experimental tests. As the proposed formula needs very low computational time and depends directly on the geometrical parameters, it is used for a design optimization using multiobjective genetic algorithms.

Torque Estimation in High-Efficency IPM Synchronous Motor Drives

In modern electrical drives, the energy saving starts with the careful generation of the electromagnetic torque, which involves the electrical motor and its current control. A modern choice is represented by an anisotropic synchronous interior permanent magnet (IPM) motor combined with the maximum torque per ampere (MTPA) control technique. The MTPA locus brings along additional information that is worth deepening. In particular, this paper shows that a proper rearrangement of the torque expression in MTPA condition, merged with a simple least-square algorithm, returns an accurate online estimation of the electromagnetic torque. The effectiveness of the proposed method is proved by a worked out example, based on an IPM drive model fitted with finite-element analysis and experimental measurements, including motor saturation effects. The torque estimator extends its usability in the whole working region of the drive, even during transients outside the MTPA curve, and it comes almost for free. In this, the proposed method should be technically sound in many industrial applications.

Bone response to a novel Ti–Ta–Nb–Zr alloy

Commercially pure titanium (cp-Ti) is regarded as the state-of-the-art material for bone-anchored dental devices, whereas the mechanically stronger alloy (Ti–6Al–4V), made of titanium, aluminum (Al) and vanadium (V), is regarded as the material of choice for high-load applications. There is a call for the development of new alloys, not only to eliminate the potential toxic effect of Al and V but also to meet the challenges imposed on dental and maxillofacial reconstructive devices, for example. The present work evaluates a novel, dual-stage, acid-etched, Ti–Ta–Nb–Zr alloy implant, consisting of elements that create low toxicity, with the potential to promote osseointegration in vivo. The alloy implants (denoted Ti–Ta–Nb–Zr) were evaluated after 7days and 28days in a rat tibia model, with reference to commercially pure titanium grade 4 (denoted Ti). Analyses were performed with respect to removal torque, histomorphometry and gene expression. The Ti–Ta–Nb–Zr showed a significant increase in implant stability over time in contrast to the Ti. Further, the histological and gene expression analyses suggested faster healing around the Ti–Ta–Nb–Zr, as judged by the enhanced remodeling, and mineralization, of the early-formed woven bone and the multiple positive correlations between genes denoting inflammation, bone formation and remodeling. Based on the present experiments, it is concluded that the Ti–Ta–Nb–Zr alloy becomes osseointegrated to at least a similar degree to that of pure titanium implants. This alloy is therefore emerging as a novel implant material for clinical evaluation.

Radiation torque, streaming, and viscous absorption due to orthogonal waves in slightly viscous fluids

Torque generated by orthogonal waves in slightly viscous fluids is analyzed to explore its connection with the near-boundary viscous absorption and streaming [Zhang and Marston, J. Acoust. Soc. Am. 131, 2917–2921 (2014)]. The analysis is based on a viscous correction and beam superposition of vortex fields. The analysis reports an approximation for the torque on a compressible small solid sphere and the viscous power absorption [Eqs. (15) and (21) in Zhang and Marston]. The torque expression in the dense sphere limit recovers prior expressions using near-boundary flow and streaming analyses: [Busse and Wang, J. Acoust. Soc. Am. 69, 1634–1638 (1981)] and [Lee and Wang, J. Acoust. Soc. Am. 85, 1081–1088 (1989)]. Our analysis extends prior results to give the torque on small compressible solid spheres of finite mass. The torque does not depend explicitly on the compressibility of the sphere, but does depend on the density of the sphere. Our analysis also gives the proportional relationship between the torque and the near-boundary viscous absorption. The results are generalized to cases of standing orthogonal waves and acoustic vortex fields, and other small axisymmetric obstacles such as circular cylinders and disks. [Work supported by the 2013-14 F. V. Hunt Postdoctoral Fellowship (Zhang) and by ONR (Marston).]

Myths and realities in orthodontics.

Comprehensive orthodontic treatment typically comprises an initial phase of alignment over a period of four to six months, followed by vertical, transverse and antero-posterior corrections, space closure, finishing and detailing to enhance dental and facial aesthetics and function. Each course of treatment involves a series of decisions and alternatives relating to objectives, appliance design and treatment mechanics. In recent years there has been increasing interest in short-term approaches to treatment with more limited objectives and the avoidance of phases traditionally considered integral to successful treatment. In this review the veracity of accepted truths in orthodontics are discussed; specifically, the importance of initial molar relationship, final incisor relationship, the merits of orthodontic extractions, anticipated treatment times, the value of modern fixed appliance systems, the importance of torque expression and the relative merits of bonded retainers and inter-proximal reduction are considered.

Investigation into the effects of stainless steel ligature ties on the mechanical characteristics of conventional and self-ligated brackets subjected to torque

Torque is applied to orthodontic brackets in order to alter the buccal-lingual angulation of a tooth. One factor that can affect torque is the ligation mode used to retain the archwire in the bracket slot. The objective of this study was to investigate the effects of stainless steel ligation on torque expression and bracket deformation. This study utilized 60 upper right central incisor Damon Q brackets and 60 Ormco Orthos Twin brackets. The brackets used in this study were subdivided into four groups: (1) Damon Q ligated with SS ligature; (2) Damon Q with the sliding bracket door; (3) Orthos Twin bracket ligated with SS wire; and (4) Orthos Twin ligated with elastic ties. All brackets were tested using an orthodontic torque simulating device that applied archwire rotation from 0° to 45°. All brackets ligated with stainless steel ties exhibited greater torque expression and less deformation than brackets without stainless steel ties. As well, Damon Q brackets exhibit less bracket deformation than Orthos Twin brackets. Stainless steel ties can reduce the amount of plastic deformation for both types of brackets used in this study.

Studies on Inertial Effect of Transmission Device Components

The inertial effects of the components in the transmission device have both advantages and disadvantages and can not be unavoidable, it has direct influences on starting, braking, energy consumption and the equipment service life, it is one of the important problems need to be discussed carefully. Using the mechanics principle, this paper analyzed the calculation method of inertial effect in gear, and obtained the torque expression of the different sections in the transmission chain and the power factor of inertia effect, the results of the given numerical example show the correctness of the conclusions/

A normative study to evaluate inclination and angulation of teeth in North Indian population and comparision of expression of torque in preadjusted appliances.

Aim:The aim of this study was to evaluate angulation and inclination of teeth from the study models of individuals with normal occlusion and evaluation of actual expression of torque expressed by three different bracket systems.Materials and Methods:In this study, the inclination and angulation were measured on 30 study models of North Indian individuals. A self-developed instrument (torque angle gauge) was used for the measurement. Fifteen study models were duplicated for the evaluation of torque expression in the bracket of three different manufacturers with different shape and size of bases.Results:The results give the mean, minimum and maximum, standard deviation of the normative data individually for each tooth. A significant correlation was noted in the angulation of maxillary canine and first premolar, and between premolars; and between mandibular central incisor with lateral incisor and canine, and between premolars.Conclusions:There was a highly significant correlation of teeth angulation and inclination in the maxillary and mandibular arch. Though the error in expression of torque was not significant, but it showed a large range, indicating the need to vary the position of brackets in different bracket systems for achieving optimum torque.

Residents' journal review

Residents' journal review

Mechanical properties of nickel-titanium archwire used in the final treatment phase of Tip-Edge Plus technique: an in vitro study

Background As the only active component in final treatment phase of Tip-Edge Plus technique, the activation of nickel-titanium orthodontic archwires is one of the factors that affect the torque expression. It is necessary to evaluate the mechanical properties of the nickel-titanium wire used in the final treatment phase in simulated oral environments to forecast the treatment outcomes. Methods The mechanical properties of 171 thermal nickel-titanium wires of 0.35 mm (0.014-in) in diameters with different deflection of 40 mm in length were investigated with three-point bending test. The samples were divided into 2 groups: as-received and bended groups. In the bended group, samples were divided into 7 subgroups according to the amounts of deflection and named by the canine angulations (−25°, −19°, −13°, −7°, −1°, +5°, +11°). The deflection of wires was made by inserting the wires into the deep tunnel of Tip-Edge Plus brackets positioned in plaster casts with different canine angulations to mimic the use of nickel-titanium wires in the final treatment phase. Immersed the bended group in artificial saliva (pH 6.8) and preserved at 37.0°C. Eight durations of incubation were tested: 1 to 8 weeks. Three analogous samples of each group and subgroups were tested per week. Stiffness (YS:E) and the load-deflection characteristics of unloading plateau section were obtained. Results Significant changes in specific mechanical properties were observed in long-term immersed and large deflected wires compared with as-received groups. Both immersion time and deflection affected the mechanical properties of wires in the simulated oral environment, and the two factors had synergistic effect. In groups −25°, −19° and −13°, stiffness (YS:E) increased then decreased and average plateau force and ratio of variance decreased then increased correspondingly at specific time. Conclusions In the final treatment phase of Tip-Edge Plus technique, the mechanical properties of nickel-titanium wire are associated with the using time and amounts of deflection and it may affect treatment outcomes. As the main reason for wire deflection, canine crown angulation plays an important role in the wire performance. It may be wise to focus on the canine crown angulations and using time in clinic with Tip-Edge Plus technique and make proper adjustment to help to make sure the treatment outcomes.

Torque expression of 0.018 and 0.022 inch conventional brackets

The aim of this study was to assess the effect of the moments generated with low- and high-torque brackets. Four different bracket prescription-slot combinations of the same bracket type (Mini Diamond® Twin) were evaluated: high-torque 0.018 and 0.022 inch and low-torque 0.018 and 0.022 inch. These brackets were bonded on identical maxillary acrylic resin models with levelled and aligned teeth and each model was mounted on the orthodontic measurement and simulation system (OMSS). Ten specimens of 0.017 × 0.025 inch and ten 0.019 × 0.025 inch stainless steel archwires (ORMCO) were evaluated in the low- and high-torque 0.018 inch and 0.022 inch brackets, respectively. The wires were ligated with elastomerics into the brackets and each measurement was repeated once after religation. Two-way analysis of variance and t-test were conducted to compare the generated moments between wires at low- and high-torque brackets separately. The maximum moment generated by the 0.017 × 0.025 inch stainless steel archwire in the 0.018 inch brackets at +15 degrees ranged from 14.33 and 12.95 Nmm for the high- and low-torque brackets, respectively. The measured torque in the 0.022 inch brackets with the 0.019 × 0.025 inch stainless steel archwire was 9.32 and 6.48 Nmm, respectively. The recorded differences of maximum moments between the high- and low-torque series were statistically significant. High-torque brackets produced higher moments compared with low-torque brackets. Additionally, in both high- and low-torque configurations, the thicker 0.019 × 0.025 inch steel archwire in the 0.022 inch slot system generated lower moments in comparison with the 0.017 × 0.025 inch steel archwire in the 0.018 inch slot system.

A comparative assessment of torque generated by lingual and conventional brackets

The aim of this study was to assess the effect of bracket type on the labiopalatal moments generated by lingual and conventional brackets. Incognito™ lingual brackets (3M Unitek), STb™ lingual brackets (Light Lingual System; ORMCO), In-Ovation L lingual brackets (DENTSPLY GAC), and conventional 0.018 inch slot brackets (Gemini; 3M Unitek) were bonded on identical maxillary acrylic resin models with levelled and aligned teeth. Each model was mounted on the orthodontic measurement and simulation system and 10 0.0175 × 0.0175 TMA wires were used for each bracket type. The wire was ligated with elastomerics into the Incognito, STb, and conventional brackets and each measurement was repeated once after religation. A 15 degrees buccal root torque (+15 degrees) and then a 15 degrees palatal root torque (-15 degrees) were gradually applied to the right central incisor bracket. After each activation, the bracket returned to its initial position and the moments in the sagittal plane were recorded during these rotations of the bracket. One-way analysis of variance with post hoc multiple comparisons (Tukey test at 0.05 error rate) was conducted to assess the effect on bracket type on the generated moments. The magnitude of maximum moment at +15 degrees ranged 8.8, 8.2, 7.1, and 5.8 Nmm for the Incognito, STb, conventional Gemini, and the In-Ovation L brackets, respectively; similar values were recorded at -15 degrees: 8.6, 8.1, 7.0, and 5.7 Nmm, respectively. The recorded differences of maximum moments were statistically significant, except between the Incognito and STb brackets. Additionally, the torque angles were evaluated at which the crown torque fell well below the minimum levels of 5.0 Nmm, as well as the moment/torque ratio at the last part of the activation/deactivation curve, between 10 and 15 degrees. The lowest torque expression was observed at the self-ligating lingual brackets, followed by the conventional brackets. The Incognito and STb lingual brackets generated the highest moments.

Comparison of deformation and torque expression of the orthos and orthos Ti bracket systems

Orthodontic torque expression is the result of axial rotation of rectangular archwires within a rectangular bracket slot. This study investigates the effect of bracket material on torque expression. Torque exerted by a rotating archwire on each bracket will be measured as well as the relative deformation of each bracket slot. A total of 60 tests were performed where archwires were rotated within a bracket slot to produce torque within a bracket. Thirty Ormco Orthos Ti and 30 Orthos SS were compared to investigate the effect of torque on bracket material. Each bracket was mounted on a six-axis load cell that measured forces and moments in all directions. The archwire was rotated from an initial angle of 0 degree in 3 degrees increments to maximum angle of 51 degrees and then returned to the initial position. An overhead camera took images at each 3 degrees increment. The bracket images were post-processed using a digital image correlation technique to measure the relative deformation of each bracket slot. The maximum torque expressed at 51 degrees was 99.8 Nmm and 93.0 Nmm for Orthos Ti and Orthos SS, respectively. Total plastic deformation measured at 0 degrees post-torquing of the Orthos SS was 0.038 mm compared to 0.013 mm for Orthos Ti. The Orthos Ti brackets plastically deformed less than the Orthos SS brackets after torquing. The Orthos SS bracket plastic deformation was 2.8 times greater than that of Orthos Ti brackets. The Orthos Ti brackets expressed more torque than the stainless steel brackets but exhibited substantial variation.

On type-I migration near opacity transitions. A generalized Lindblad torque formula for planetary population synthesis

We give an expression for the Lindblad torque acting on a low-mass planet embedded in a protoplanetary disk that is valid even at locations where the surface density or temperature profile cannot be approximated by a power law, such as an opacity transition. At such locations, the Lindblad torque is known to suffer strong deviation from its standard value, with potentially important implications for type I migration, but the full treatment of the tidal interaction is cumbersome and not well suited to models of planetary population synthesis. The expression that we propose retains the simplicity of the standard Lindblad torque formula and gives results that accurately reproduce those of numerical simulations, even at locations where the disk temperature undergoes abrupt changes. Our study is conducted by means of customized numerical simulations in the low-mass regime, in locally isothermal disks, and compared to linear torque estimates obtained by summing fully analytic torque estimates at each Lindblad resonance. The functional dependence of our modified Lindblad torque expression is suggested by an estimate of the shift of the Lindblad resonances that mostly contribute to the torque, in a disk with sharp gradients of temperature or surface density, while the numerical coefficients of the new terms are adjusted to seek agreement with numerics. As side results, we find that the vortensity related corotation torque undergoes a boost at an opacity transition that can counteract migration, and we find evidence from numerical simulations that the linear corotation torque has a non-negligible dependency upon the temperature gradient, in a locally isothermal disk.

Mechanical effects of third-order movement in self-ligated brackets by the measurement of torque expression

Axial rotation of orthodontic wire produces buccal or lingual root movement and is often referred to as third-order movement or "torque expression." The objective of this study was to quantify torque expression in 3 self-ligation bracket systems (Damon Q, Ormco, Orange, Calif; In-Ovation R, GAC, Bohemia, NY; and Speed, Strite Industries, Cambridge, Ontario, Canada) during loading and unloading. A stepper motor was used to rotate a wire in a fixed bracket slot from -15° to 63° in 3° increments, and then back to -15°. The bracket was mounted on top of a load cell that measured forces and moments in all directions. Damon's and In-Ovation's maximum average torque values at 63° were 105 and 113 Nmm, respectively. Many Speed brackets experienced premature loss of torque between 48° and 63°, and the average maximum was 82 Nmm at 54°. The torque plays for Damon, In-Ovation, and Speed were 11.3°, 11.9°, and 10.8°, respectively. Generally, In-Ovation expressed the most torque at a given angle of twist, followed by Damon and then Speed. However, there was no significant difference between brackets below 34 Nmm of torque. From a clinical perspective, the torque plays between brackets were virtually indistinguishable.