Multistranded Wires Research Articles

Heat transport with a twist.

Despite the desirability of polymers for use in many products due to their flexibility, light weight, and durability, their status as thermal insulators has precluded their use in applications where thermal conductors are required. However, recent results suggest that the thermal conductance of polymers can be enhanced and that their heat transport behaviors may be highly sensitive to nanoscale control. Here we use non-equilibrium molecular dynamics simulations to study the effect of mechanical twist on the steady-state thermal conductance across multi-stranded polyethylene wires. We find that a highly twisted double-helical polyethylene wire can display a thermal conductance up to three times that of its untwisted form, an effect which can be attributed to a structural transition in the strands of the double helix. We also find that in thicker wires composed of many parallel strands, adding just one twist can increase its thermal conductance by over 30%. However, we find that unlike stretching a polymer wire, which causes a monotonic increase in thermal conductance, the effect of twist is highly non-monotonic, and certain amounts of twist can actually decrease the thermal conductance. Finally, we apply the Continuous Chirality Measure (CCM) in an attempt to explore the correlation between heat conductance and chirality. The CCM is found to correlate with twist as expected, but we attribute the observed heat transport behaviors to structural factors other than chirality.

Vibration-based tension estimation of short helically multi-stranded wires under low axial tension

When cables are used to support systems, accurate tension monitoring is critical. However, almost all existing tension estimation models are inaccurate for short cable under low tension. Short helically stranded wire cables under low axial tension are widely used especially in cable-driven robots (CDRs). A vibration-based equation accurately to evaluate applied tensions for short helically stranded wires under low axial tension was developed. We employed two kinds of short cables with diameters of 2.4 and 3.2 mm under tensions of approximately 20 to 110 N. There were no known tension estimates for these conditions up to now. We used a best-fit numerical approach (employing the measured first frequencies and C/f1 values) to derive an accurate equation. The helically stranded wire theory was also used to validate the feature. Finally, we verified experimentally the derived equation using different material and different diameters and the estimates agreed with the experimental data well.

Efficacy of CAD/CAM Technology in Interventions Implemented in Orthodontics: A Scoping Review of Clinical Trials.

Objectives To evaluate the efficacy of computer-aided design/computer-aided manufacturing (CAD/CAM) technology in interventions implemented in orthodontics. Methods A scoping review of scientific evidence was accomplished, involving different databases. MesH terms and keywords were provided to examine clinical trials (CTs) in all languages. Exclusively CTs that fulfilled the eligibility criteria were admitted. Results Eight CTs were chosen. These experiments evaluated 542 patients. Four CTs compared the computer-aided indirect bonding method versus the traditional direct bonding of orthodontic brackets. Three CTs compared CAD/CAM retainers with other types of retainers, and one CT compared the CAD/CAM group with multistranded stainless steel wires versus stainless steel wires. Regarding the efficacy of the interventions with CAD/CAM technology used in orthodontics, variable results were found. The indirect bonded customized CAD/CAM brackets presented just a slight effect on the treatment efficacy and therapy results. Two CTs showed that an indirect bonding self-ligating standard system had a similar quality of therapy in comparison with the CAD/CAM customized bracket system. Concerning the clinical failure rate, no differences were presented between the CAD/CAM retainer and other retainers. A CAD/CAM system had more loose brackets than a noncustomized system and was observed also a greater amount of immediate debonding with CAD/CAM indirect bonding than with direct bonding. CAD/CAM fixed retainers revealed inferior relapse and fewer failures than lab-based and conventional chairside retainers. No changes between treatment groups were observed regarding the total therapy time, amount of appointments, and quantity of archwire bends. Conclusions In general terms, no greater efficacy of CAD/CAM technology was observed over traditional therapies used in orthodontics. However, it was found that gingival inflammation and the accumulation of bacterial plaque and dental calculus were lower when CAD/CAM retainers were used. When comparing interventions that include CAD/CAM systems with conventional therapies, no significant reduction in care times was found.

Comparative assessment of relapse and failure between CAD/CAM stainless steel and standard stainless steel fixed retainers in orthodontic retention patients.

To compare relapse and failure rates of computer-aided design/computer-aided manufacturing (CAD/CAM) and standard fixed retainers. This single-center, single-blinded, prospective randomized clinical trial included 46 patients who completed active orthodontic treatment and complied with retention visits. The patients were randomly assigned to three groups: CAD/CAM group with multistranded stainless steel wires (CAD/CAM, n = 16), Lab group with the same multistranded wires (lab, n = 16), and control group with stainless steel Ortho-FlexTech wires (traditional, n = 14). Intraoral scans were obtained at placement of fixed retainers (T1), 3-month visit (T2), and 6-month visit (T3) and measured for intercanine width and Little's Irregularity Index. Failures were recorded. The CAD/CAM group experienced less intercanine width decrease than the traditional group at 3 months (mean difference, 0.83 ± 0.16 mm; 95% confidence interval [CI], 0.44-1.22; P < .001) and 6 months (mean difference, 1.23 ± 0.40 mm; 95% CI, 0.19-2.27; P < .05). The CAD/CAM group experienced less increase in Little's Irregularity Index compared with the lab group within 3 months (mean difference, 0.81 ± 0.27 mm; 95% CI, 0.12-1.49; P < .05). Failures from greatest to least were experienced by the lab group (43.8%), the CAD/CAM group (25%), and the traditional group (14.3%). Within 6 months of bonding fixed retainers, CAD/CAM fixed retainers showed less relapse than lab-based and traditional chairside retainers and less failures than lab-based retainers.

Advances in orthodontic archwires

Recent advances in orthodontic wire alloys have resulted in a varied array of wires that exhibit a wide spectrum of properties. Up until the 1930s, the only orthodontic wires available were made of gold. Subsequently, stainless steel was introduced and due to its superior properties gained popularity over gold. The introduction of nickel-titanium archwires revolutionized the orthodontic field with their shape memory &amp; superelasticity. Several other alloys with desirable properties have been adopted in orthodontics. These include cobalt-chromium, beta titanium and multi-stranded stainless steel wires. The availability of archwires with widely diverging properties has profound implications on appliance mechanics and can be used to advantage at different stages of orthodontic treatment. The newer archwires score over conventional wires in terms of efficiency, total treatment time, and finishing. Also, the current emphasis on esthetic treatment options in orthodontics has led to the development of esthetic archwires. Presently the orthodontist may select, from all the available wire types, one that best meets the demands of a particular clinical situation. The selection of an appropriate wire size and alloy type in turn would provide the benefit of optimum and predictable treatment results.

In vitro comparison of the torsional load transfer of various commercially available stainless-steel wires used for fixed retainers in orthodontics.

To assess the torsional load transfer of various commercially available stainless-steel wires used for fixed retainers. An in vitro study using a robotic device. Department of Pediatric Oral Health and Orthodontics, University of Basel. A 10° proclination of a maxillary lateral incisor of a 2-2 retainer was simulated with a robotic device. Eight stainless-steel wires with different shapes (round or rectangular), types (plain, braided, coaxial or chain) and dimensions were selected to measure the torsional load transfer at the adjacent central incisor. The influence of annealing was also tested. The 0.016 × 0.016 and Bond-A-Braid™ wires (0.02645 × 0.01055-inch, 8-stranded, braided) showed the largest relative torsional load transfer (3.7% and 3.3%, respectively). The two multistranded wires - Triple Flex™ and Respond® - showed the smallest values of 1.0% and 0.7%, respectively. The spiral direction of these two multistranded wires affected the load transfer, the twisting showing larger torsional load transfer than the untwisting one. The effective torsional load transfer depends on the dimension, shape and type of a wire. Plain and braided retainers were more predictable in torsional load transfer than multistranded retainers, which may have stored more energy in the area between the composite bonding sites. This may explain the unexpected complications reported in multistranded retainers.

Unlocking ectopically erupting permanent first molars using light wires

Background and OverviewEctopic eruption of permanent molars is one of the challenges that arise in the early mixed dentition period, particularly when the root of the primary second molar is resorbed due to mesial angulation of the impacted first molar. The authors introduce a simple and efficient method to unlock ectopically erupting first molars using a light wire. Case DescriptionThe authors describe the cases of 2 girls (8 and 7 years old) who sought treatment for locking of their maxillary and mandibular first molars, respectively. A 0.012-inch nickel titanium wire was compressed and bonded to the first molars and primary second molars to unlock the first molars. The primary second molars were splinted to the adjacent primary first molars and canines using bonded multistranded wires. As the compressed wires straightened over time, the locked first molars were tipped back without any substantial mesial movement of the primary teeth. After unlocking the molars, the nickel titanium wires were removed to allow spontaneous eruption of the first molars. Conclusions and Practical ImplicationsAlthough the primary molar roots were considerably resorbed, the ectopically erupting first molars were unlocked successfully without any substantial movement of the primary teeth. The clinical procedure was simple, and no laboratory procedures were needed. In addition, the anchorage burden was reduced with the use of light forces. The authors suggest that primary second molars with substantial root resorption due to ectopic eruption of permanent first molars can be saved simply and efficiently.

Clinical comparison between Multi-Stranded Wires and Single strand Ribbon wires used for lingual fixed retainers

BackgroundLong-term retention with fixed retainers with a high success rate seems to be a reasonable solution to minimize or prohibit relapse of orthodontic treatment.MethodsTwo hundred sixty patients between 13 and 30 years old were recruited for this study. The 0.0175 stainless steel twisted wire (G&H Orthodontics, USA) was compared with a single-strand ribbon titanium lingual retainer wire (Retainium, Reliance orthodontics, USA) was used. When treatment was completed, the retainers were bonded from canine to canine in the mandibular arch of the participants. In the follow-up visits, the patients were recalled every 3 months during the 24 months. Detachments, the time of debonding, and side effects were recorded. Statistical analysis was performed by a blinded statistician using a statistical package for Social Science (SPSS, Version20). After descriptive statistics, Kaplan-Meier analysis was performed to measure the survival rates of each retainer. P value < 0.05 was considered as significant.ResultsFinally, 138 patients who received twisted wire splint and 112 patients who received ribbon wire were included in the analysis. The average duration of success was about 23 months for twisted wire and ribbon wire, according to the Kaplan-Meier estimates. The analysis showed no significant overall difference between the treatments (p = 0.13). Failure rates in terms of detachments in all groups occurred at the enamel junction, and it was 25 in twisted retainer group (18.1%) and was 10 in ribbon retainer group (8.9%); the Kaplan-Meier analysis test detected a significant difference in the failure rates between the groups (p = 0/006).ConclusionsAlthough the conventional twisted stainless steel wire and single-strand titanium flat metal ribbon wire as fixed orthodontic retainers have the same clinical effects, it was shown that the ribbon wire has less failure in terms of detachments.

A recursive methodology for modelling multi-stranded wires with multilevel helix structure

Multi-stranded litz wires are commonly used in magnetic devices for power electronics applications at medium-high frequency range, from several kHz up to hundreds of kHz. For these applications, litz-wire structure favours the uniformity of driven current in the cross-sectional area of conductors, alleviating ac losses (skin and proximity effects) and improving the global efficiency of the application. These features are achieved by means of a special cable arrangement consisting of many isolated fine copper strands twisted together according to the manufacturing process. Often, the manufacturing process involves several twisting steps where bundles of moderate number of strands are successively twisted resulting in intricate cable structures. We present a mathematical description of the trajectories of copper strands with the purpose of obtaining the cable losses by means of Finite Element Analysis (FEA) simulation tools. Moreover, a nomenclature for this multilevel structures is also proposed. Parameters as the number of twisting steps, number of strands, strand diameter or pitch length, are included in this representation, allowing to compare the performance of different manufacturing solutions.

Enhancing of Operational Reliability of Catenary and Electric Rolling Stock Wire Connections

The article deals with technological possibilities of operation reliability enhancement of high-current electrical connections while assembling unattended assembly joints under the pressure of pulsed magnetic field. The results of numerical modeling and experimental research of the catenary assembly process for the monometallic, bimetallic and composite multistranded wires between themselves and between them and terminals including those resulting vias made of aluminum and copper. The results of heat and electric tests of resulted connections are presented. It is ascertained that mechanical breaking strength of connections obtained under the pressure of pulsed magnetic field reaches 98…100% of intact wire strength. The factors of electrical contact defectiveness per resistance and per overtemp with rated current while making magnetic-impulse assembly of a wire and a coupling are lower than limit values, which are established for connections of feed wires, connectors and connecting clamps, which are obtained by pressing.

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.

Periodontal effects and survival rates of different mandibular retainers: comparison of bonding technique and wire thickness.

This non-randomized prospective cohort study aimed to compare the periodontal effects and success rates of mandibular canine-to-canine fixed retainers having different bonding techniques and wire thicknesses. Hundred patients requiring retention after orthodontic treatment were assigned to five study groups (n = 20 in each group, 61 females/39 males, median age range 16.5-18.0 years). Retention was provided by 0.0215"/direct, 0.0215"/indirect, 0.0175"/direct, 0.0175"/indirect bonded multistranded wires and removable Essix appliances. The primary and secondary outcomes were periodontal effects and success rates. The patients were examined in 1 week, 1 month, 3 months and 6 months follow-up appointments. Plaque index, gingival index, probing depth, marginal recession, bleeding on probing, failure rate per retainer wire and survival of retainer wires were analysed by Kruskal-Wallis H, Mann-Whitney U and chi-square tests. Significant differences were observed between the fixed retainer (FR) and Essix (E) groups in gingival index scores at 1 month [mean FR: 1.13 (95% confidence interval (CI): 0.81-1.44), mean E: 0.40 (95% CI: 0.14-0.69), mean difference: 0.73, P < 0.01], 3 months [mean FR: 0.97/1.01 (95% CI: 0.65-1.30/0.72-1.30), mean E: 0.52 (95% CI: 0.25-0.82), mean differences: 0.45/0.49, P < 0.05], 6 months [mean FR: 0.94 (95% CI: 0.62-1.27), mean E: 0.35 (95% CI: 0.15-0.58), mean difference: 0.59, P < 0.05] and in bleeding on probing scores at 1 month [mean FR: 3.05 (95% CI: 2.12-3.98), mean E: 1.15 (95% CI: 0.42-1.88), mean difference: 1.90, P < 0.01]. The survival rates of retainer wires were 85 per cent for the 0.0215" direct/indirect and 90 per cent for the 0.0175" direct/indirect groups for the 6 months follow-up. Six months follow-up period, which demonstrates only short-term outcomes. The periodontal outcomes or survival rates of mandibular fixed retainers were not affected by bonding technique or wire thickness, whereas gingival health improved with Essix retainers but not with fixed retainers.

Electrochemically Stable and Adherent PEDOT Coatings for High Quality EMG Recording

Conductive polymers coatings on metal electrodes are an efficient solution to improve neural signal recording and stimulation due to their mixed electronic-ionic conduction and biocompatibility [1]. However, only a few studies have been reported on conductive polymers coatings on metallic wire electrodes for muscle signal recording [2,3]. In this work, we developed mechanically and electrochemically stable invasive electrodes for muscle signal recording in small animals based on stainless steel multi-stranded wires coated with the conductive polymer PEDOT. PEDOT doped with LiClO4 was galvanostatically electropolymerized on stainless steel wires using three different solvents: propylene carbonate (organic), acetonitrile (organic) and water (inorganic). The coatings adhesion to the metallic substrate was tested through ultrasonication and the electrochemical stability was evaluated through phosphate buffer solution soaking test and autoclave sterilization. The solvent played a key role on the adhesion of the PEDOT coating, with organic solvents giving the best mechanical stability. Electrodes prepared with these solvents possessed excellent electrochemical stability and survived sterilization and prolonged soaking without major changes in electrochemical properties. A solution for high quality invasive muscle signal recording in small animals based on conductive polymers has been demonstrated.

ANTIBACTERIAL ACTIVITY OF SILVER NANOPARTICLES ON FIXED RETAINER ADHESIVE TOWARD TREPONEMA DENTICOLA

Objective: The objective of this study was to develop an antibacterial flowable composite containing silver nanoparticle (AgNP) for the prevention ofperiodontal disease in fixed retainers.Methods: About 1% AgNP was incorporated into a commercial composite (tetric flow). The experimental and control products were used to bondfixed retainers to 28 extracted mandibular first premolars. The samples were randomly divided into four groups (n=7): Premolar bonded withfiber-reinforced composites and tetric flow (F1); premolar bonded with fiber-reinforced composites and AgNP-enhanced tetric flow (F2); premolarbonded with multistranded wires (MW) and tetric flow (M1); and premolar bonded with MW and AgNP-enhanced tetric flow (M2). Each sample wassubmerged in a test tube containing bacterial Treponema denticola solution and was incubated for 24 h and 37°temperature. The bacterial colony ineach group was counted and analyzed.Results: This study showed that there was significant difference of T. denticola colony count between groups with and without AgNP-enhancedcomposites in both types of retainers.Conclusion: AgNP-enhanced flowable composites reduce the bacteria T. denticola colony count and possibly inhibit periodontal disease.

SkinWire

Current wearable form factors often house electronics using an enclosure that is attached to the body. This form factor, while wearable, tends to protrude from the body and therefore can limit wearability. While emerging research in on-skin interfaces from the HCI and wearable communities have generated form factors with lower profiles, they often still require support by conventional electronics and associated form factors for the microprocessor, wireless communication, and battery units. In this work, we introduce SkinWire, a fabrication approach that extends the early work in on-skin interfaces to shift wearable devices from their traditional box-like forms to a fully self-contained on-skin form factor. The Skin Wire approach starts with the placement of electronic components into individual PCB islands, which are then distributed over the body surface. The islands are connected through a novel skin-wiring approach that deposits conformal multi-stranded metallic wires on thin silicon substrates through a sewing-based technique. The process affords on-skin interfaces with the needed wiring in limited surface areas. We exemplify the capacity of this approach by shifting an IMU-based hand gesture system - which traditionally come in bulky glove-based form factors - directly onto the skin. Inspired by the emerging body art trend of body wiring, the Skin Wire approach uses readily accessible materials and affords aesthetic customization. We evaluate fabrication parameters, and conduct a user study to uncover wearability concerns.

A Systematic review on aligning efficiency of superelastic NITI: in comparison with conventional NITI and multistranded stainless steel archwires

Background: The initial leveling and aligning phase of orthodontic treatment involve the use of nickel titanium wires. The nickel titanium wires exhibit unique properties like shape memory and superelasticity. In the beginning, conventional nitinol wires were used, which lacked the superelastic property. Nowadays, superelastic nickel titanium wires are being used commonly. This systematic review aims to evaluate the efficiency of Superelastic NITi in the initial alignment of orthodontic treatment in comparison with conventional NiTi and multistranded stainless steel archwires by measuring the amount of decrowding and the time taken for decrowding.Method: A systematic literature search was performed on Pubmed, Cochrane, Google scholar &amp; Lilacs.Result: Thirty four studies were identified by the search and ten studies satisfied the inclusion criteria and one study was excluded after abstract reading. Finally nine articles were included for quality assessment.Conclusion: This systematic review concluded that there was no significant differences in the aligning efficiency of superelastic NiTi in comparison with conventional NiTi and multistranded stainless steel wires.Â

Comparative analysis of the mechanical properties of fiber and stainless steel multistranded wires used for lingual fixed retention

ObjectiveTo evaluate the effect of different resins used for the co-polymerization of EverStick fiber-reinforced fixed orthodontic retainer on its mechanical properties and to compare the mechanical properties of these configurations to commonly used multistrand wires. Materials and methodsTen 0.0175-in. WildCat (WC175), ten 0.0215-in. WildCat (WC215) three-strand twisted wires and thirty EverStick fibers were tested in this study. The EverStcik fibers were equally shared in three groups (n=10). The samples of first group (ESRE) were polymerized employing Stickresin (Light cure enamel adhesives), the second one (ESFT) employing Flow Tain (Light cured composite), whilst the specimens for the third group (ES) were not combined with resin. All samples were loaded in tensile up to fracture in a universal tensile testing machine and the modulus of elasticity, tensile strength and strain after fracture were recorded. The same groups were also tested employing Instrumented Indentation Testing (IIT) and Martens Hardness (HM), Indentation Modulus (EIT) and elastic index (ηIT) were determined. The results of tensile testing and IIT were statistically analyzed employing one way Anova and the Student Newman Keuls test (SNK) at a=0.05 level of significance. ResultsWC175 and WC215 showed higher modulus of elasticity and tensile strength but lower strain after fracture compared to Everstic groups. IIT illustrated significantly higher values for HM, EIT, and ηIT for WC groups compared to ESRE, ESFT and ES. ESFT showed higher HM and elastic index compared to ESRE and ES, a finding which is attributed to the fact the FlowTain is a filler-reinforce composite with higher hardness compared to unfilled resins. SignificanceMultistrand wires demonstrated higher values in mechanical properties compared to EverStick ones. The co-polymerization with difference resins does not affect the tensile properties of Everstic, however the use of a light cured composite has a beneficial effect on hardness.

Forces in initial archwires during leveling and aligning: An in-vitro study.

Aim:This in-vitro study measured the force deflection behavior of selected initial alignment archwires by conducting three-point bending tests under controlled tests. The study tested three wire designs, namely, co-axial multistranded stainless steel wires, nickel–titanium, and copper–nickel–titanium archwires.Materials and Methods:The archwires were ligated to a specially designed metal jig, simulating the arch. A testing machine (Instron) recorded activation and deactivation forces of different deflections at 37°C. Forces on activation and deactivation were compared by one-way analysis of variance (ANOVA).Results:Significant differences (P < 0.05) in activation and deactivation forces were observed among the tested wires. The co-axial multistranded wire had the lowest mean activation and deactivation forces, whereas conventional nickel–titanium wires had more mean activation and deactivation forces at different deflections.Conclusion:The activation and deactivation forces were higher for nickel–titanium followed by copper–nickel titanium and co-axial wires. The amount of percentage force loss was more for co-axial wire, indicating that these wires are not ideal for initial leveling and aligning.

Frequency-Dependent Resistance of Planar Coils in Printed Circuit Board With Litz Structure

Printed circuit board (PCB) windings are convenient for many applications given their ease of manufacture, high repeatability, and low profile. In many cases, the use of multistranded litz wires is appropriate due to the rated power, frequency range, and efficiency constraints. This paper proposes a manufacturing technique and a semianalytical loss model for PCB windings using planar litz structure to obtain a similar ac loss reduction to that of conventional windings of round wires with litz structure. Different coil prototypes have been tested in several configurations to validate the proposal.

In vitro debonding of orthodontic retainers analyzed with finite element analysis.

The aim of this in vitro study was to determine the load and deflection at failure of different lingual retainers bonded with composite to enamel in a standardized three-point bending test. The results were rationalized with finite element analysis (FEA) models. Four types of multistranded wires, Dead Soft Respond, Twisted ligature, Penta-One, Gold-plated Penta-One, and two glass fibre-reinforced composite retainers, Fibre 07 and Fibre 09, were bonded to enamel with composite and submitted to a three-point bending test. The load and deflection at failure and the mode of debonding were recorded. The stiffness of the wires was determined and all experimental data were used in FEA models to rationalize the observed values and mode of debonding. Significant higher load and deflection were found for the most flexible retainers Twisted ligature and Dead Soft Respond. All retainers failed between the wire and composite, which was confirmed by FEA showing the highest stress in the composite around the retainer. The FEA models showed that the amount of composite used for bonding the retainers should be 2-4mm. Based on the in vitro results, optimal bonding of lingual retainers can be achieved by flexible retainers, bonded with intrinsically strong composites. According to the FEA models the retainer should be bonded with 2-4mm composite, leaving the critical 'free-wire' length for the success of the retainer system.