Bending superelastic archwires — the missing constituent of orthodontic therapy

Dr. Suhail Khouri talks about wire bends and how Bendistal pliers can help put V-bends in previously unbendable wires.

Dr. Suhail A. Khouri discusses the clinical benefits of wire bending

Introduction

When superelastic archwires entered orthodontic practice, their 100% spring-back elastic property created the lightest and most consistent force delivery range, which exceeds by far the elasticity increase obtainable by wire bending. They revolutionized teeth alignment without loop bending. But the impossibility of bending those brittle wires posed the challenge of finding a special tool to activate them.1,2 This triggered the development of Bendistal pliers in 1995.3 These special pliers can insert permanent V-bends that activate those unbendable wires in all directions, leading to evolution of the new V-bend technique, which opened new potential in orthodontic therapies.4-11

How elasticity of wires creates and delivers orthodontic forces

Orthodontic force is created from the energy stored by deflecting an elastic wire to a position just before its deformation point. This force will be delivered to teeth when the deflected wire returns to its original position. Bending archwires into loops, helices, and springs aims primarily at extending the elasticity range of the distant part of the bent wire that will be engaged in the bracket’s slots. The position of this distant part of already bent wire, before being engaged in brackets, becomes the targeted final position of the teeth. So, the distance from the target position and the bracket, the bent part of the wire to be tied to, is called “activation range.” It is the same range of extended spring-back range after appliance bending. The “deactivation range” is the same spring-back range. The pushing or pulling force starts acting on tooth/teeth, consistently moving the teeth all the way until the elastic range expires, and the teeth reach the target position.

Mechanical and clinical benefits of wire bending

The following factors determine levels of archwire elasticity, magnitudes, and continuity of force-delivery:

  1. Metallurgic alloy structure of archwire exhibits its own specific level of elasticity.
  2. Cross-sectional thickness. Wire that has a thinner cross section has a longer elasticity level and range than thicker wire, and vice versa.
  3. Length of a wire. Longer wire has a higher level of elasticity and longer spring-back range than short ones, and vice versa.
  4. Bending a wire extends its elasticity, creating lighter, more consistent force that moves teeth faster with less root
  5. Bendability of a wire. Wire bending into appliances allows applying those forces in all directions.9,10

The structural elasticity properties of superelastic archwires negates the need for the four benefits of wire bending; however, their bending remains urgently needed to apply their lightest and most consistent forces in all directions on teeth. Bendistal and Omni pliers were specifically designed just to satisfy the fifth objective and resolve this mostly important requisite.11

Measuring archwire’s elasticity

The force magnitude required to deflect a wire a certain distance before it deforms is called “Load.” This maximum distance a wire can be deflected while maintaining full spring-back to its predefection position, is called “Deflection.” This is the distance along which orthodontic force is generated, delivered, and moves teeth with one adjustment. Relating the force magnitude over that distance makes the Load/Deflection ratio (L/D) ratio — the mathematical parameter that describes and measures the wire’s level of elasticity9 in gm, cm, or oz/inch. The lower value of this ratio indicates the wire’s higher elasticity that delivers lighter and more consistent force and moves teeth a longer distance with a single activation. A higher value of that ratio indicates that such wire has a lower level of elasticity, delivers stronger force magnitude, moves teeth a shorter distance, and requires frequent tying adjustments. Each wire’s metallurgic structure possesses its own level of elasticity (L/D rate) that distinguishes it from other kinds of wires.

Properties of superelastic wires

  • Are brittle and unbendable (break upon acute sharp bend angle) and lose activation when bent in an obtuse angle.
  • Have a 100% spring-back elasticity range that can move teeth the longest distance with just one tying adjustment.
  • Have the lowest L/D rate value ever produced (delivers the lightest and most consistent force delivery).
  • Maintain full activation range upon full wire-to-brackets engagement.7,10
  • Move teeth the longest distance with least number of adjustments in fastest treatment time.12,13
Figure 1: Each of the two-paired Bendistal pliers set (left) have opposite jaw configurations that determine the V-bend direction it places on an archwire. The engraved letters on each pair identifies the two mouth quadrants each pair of Bendistal pliers serves. The one-paired Omni pliers (right) has two occlusal V-shaped trenches and one double-sided rhomboidal-shaped gingival wedged jaw, which produce opposite directional bends replacing the two pairs of Bendistal pliers

Description of the Bendistal and Omni pliers (Figure 1)

Bendistal pliers’ jaws make a 45° angle to its long axis for easy intraoral manipulation and accessibility behind molar tubes. Each plier has two jaws — the occlusal jaw has a V-shaped trench, and the gingival jaw has a V-shaped gingival wedge that fits snugly in it to insert the lasting bends. A simple squeeze of those jaws will produce an optimal unbreakable activating bend. The two pairs of pliers insert V-bends in superelastic archwires in four quadrants of mouth, without annealing, breakage, or over twisting. One pair of pliers is designated to insert bends in the upper left and lower right mouth quadrants (UL-LR); and the other pair bends NiTi archwires in the upper right and lower left mouth quadrants (UR-LL). Engraved letters on both pairs of pliers help clinicians identify the correct pair that bends the archwire in the intended quadrants. Placing the pliers’ jaws around tied archwires determines the orientation of the inserted V-bend and its mechanical effect on the segments of teeth. Also, the location of the bend on the archwire determines the direction and planes of teeth segment movements as well. Vertically oriented intraoral V-bends can bend distal ends, tip back molars, and step-up/step-down, and intrude/extrude teeth. Transversely oriented V-bends activate archwires extraorally for step out/in, and arch expanding bends. The Omni Pliers is a new generation of Bendistal pliers that combines the exact jaw shapes and versatile functions of both pairs of Bendistal pliers into one pair of pliers.

Which bends can activate NiTi wires?

Because of the brittleness and superelasticity of NiTi wires, traditional pliers make bends that are shallow, quickly spring back, and lose their force-delivering ability. Inserting a permanent bend in those nonmalleable wires requires that the pliers’ bending jaws be V-shaped, not round. Bendistal and Omni pliers’ jaws design makes the bending of NiTi wires possible.

The crucial requirements for inserting the successful bends in superelastic archwires follow:

  1. Inserting a permanent V-bend capable of delivering light and consistent force requires that the tip of the bend must be sharp.
  2. The angle of the V-shaped bend must be not too acute to break the brittle wires or too obtuse to lose its force-delivering activation.
  3. The bend must hold on after forcefully engaging bent wire in bracket slots.
  4. V-bends must be inserted correctly at the first attempt. Attempting to repair a wrong bend will break the archwire, requiring replacement.
Figures 2A-2C: Illustrates UL-LR pliers’ occlusal jaw placed under straight wire during the bending process. 2A and 2B. Wrong wire-to-jaw snout angles resulting in deflecting bent parts of the wires in wrong direction (in red) and planes, away from wire’s straight-line continuity. 2C. Shows the correct 90° angle of wire-to-snout relationship that deflects the bent part of the wire in line and in a plane with the rest of the wire’s line

Inserting correct bends in straight NiTi wires (Figure 2)

Bendistal and Omni pliers’ jaws were optimally designed to insert successful unbreakable lasting V-bends, which do not dissipate upon bracket tying. Orienting these bends in the correct locations — the wire’s line and imaginary plane that moves teeth in the planned path — poses a challenge. This requires observing certain specific rules that instruct the correct orientation of the pliers’ jaw snout to lines and planes of archwires. These rules ensure inserting the correct bends that activate to apply their forces in the prescribed paths of teeth movements (Figure 2). Round and rectangular wires tend to slip during the bending process due to their elasticity and brittleness. This difficulty can be overcome by grabbing the wire in a correct orientation with a firm grip before squeezing plier jaws. If the wire slips after a loose grip, the bend will activate the wire in a wrong path of tooth movement.

Rules that ensure inserting correct V-bends in all planes follow:

  1. The pliers’ jaws must grab the wire with a firm grip at a right angle (Figure 2C)
  2. If the wire slips while bending due to lose grip, the bend will result in an obtuse or acute angle, activating the wires in a wrong direction and moving the teeth in unwanted oblique planes (Figures 2A and 2B).
Figures 3A-3C: Inserting intrusive V-bends on maxillary preformed archwires. 3A. When occlusal jaw of Bendistal or Omni pliers is placed under the archwire plane, making an obtuse anterior angle with the line of the archwire, the resulting V-bend deflects wire up, but out in a wrong plane (in yellow). 3B. When the occlusal jaw snout makes acute angle with wire line, the bent part deflects up but in a wrong inward plane to archwire’s plane and line. 3C. The correct grip right angle between snouts to wire line will deflect the wire correctly and in a vertical plane to the archwire’s plane. For horizontal V-bends, step-in/step-out and crossbite midline bends, the snout of the pliers’ jaws should make a right angle with the imaginary plane of the preformed archwire. Otherwise, the wire deflection will cause extrusion or intrusions of the affected teeth in unwanted oblique directions

Inserting correct vertical intruding bends in preformed NiTi archwires (Figures 3 and 4)

When inserting intrusion vertical bends in maxillary preformed NiTi archwire in the upper left quadrant, follow these rules:

  1. Place the occlusal jaw of UL-LR Bendistal pliers under and in line with the imaginary archwire’s plane.
  2. Pointing the tip of pliers’ jaws down or up to the archwire plane will deflect bent wire in a wrong oblique unwanted plane (Figures 3A and 3B).
  3. Incorrect angle relation of the pliers’ snout to the archwire plane deflects wire in an incorrect intruding V-bend
    (Figures 3A and 3B).
  4. Only observing the 90° angle rule to wire line, with jaws’ snout in line with archwire’s plane, produces correct intruding bend (Figure 4C).
Figures 4A-4C: Samples of types of V-bends possible in superelastic archwires. 4A. Shows crossbite, midline expanding, and constricting bends. 4B. Shows transverse bends: step-out/step-in, and mushroom bends. 4C. Shows vertical bends: cinch-back; step-up/step-down, and intrusion bends

Inserting transverse bends

To insert correct transverse V-bends that activate NiTi wires, the pliers’ snout must make a 90° angle to the archwire’s imaginary plane. At the same time, the snout should make a right angle with the archwire’s line sideways and anterio-posteriorly. Those two requirements ensure inserting bends in line with the archwire’s plane and wire’s line. Any deviation from that rule results in activating the bends in a different plane than the archwire’s. These bends are used to correct crossbites (expanding and constricting dental arches). Such bends include midline bends, canine constrictive or expanding bends, step-out, step-in bends, and mushroom bends (Figure 4A-4C).

Figures 5A-5C: Shows examples of V-bends that turn regular tied NiTi archwires into instant and effective appliances without customizing multilooped-bends necessary in stainless steel archwires. 5A. Shows possibility of placing intraoral bends in distal end behind molar tube and molars tip-back bends in NiTi archwires, which helps erupt second premolars. 5B. Shows the intrusive effect of V-bends inserted intraorally behind canine areas of maxillary and mandibular archwires. In this case, the activated archwires were left in place for an extended period of time, resulting in overtreatment. 5C. Shows insertion of extra V-bends in both maxillary and mandibular archwires to tipback molars and protects their anchorage, and helps erupting blocked second premolars. This force system’s intrusion of incisors and extrusion of canines and premolars enhance teeth disengagement, which allows easy mandibular incisors retraction and Class III treatment without orthognathic surgery

Types of vertical intraoral V-bends

After clinicians master the preceding bending rules, extraorally, they can insert correct V-bends intraorally to activate tied NiTi archwires in the vertical direction. These bends include cinch-back bends without annealing; molar tip-back, anchorage, and space-regaining bends for second premolar eruption; and intrusion bends for anterior and posterior teeth segments (Figures 5A and 5B). When making intraoral V-bends, clinicians must observe all previously mentioned rules for correct lasting bends in a plane perpendicular to the archwire’s plane. Any oblique tilt of the pliers’ jaws before squeezing the pliers’ jaws will result in a wrong wire deflection that moves teeth in an unwanted oblique direction. For both mandibular and maxillary molar’s cinch-back, tip-back, and incisor segments intrusion, place the pliers’ occlusal jaw occlusal to the wires; and gingival jaw gingival to the wire. All intrusive bends produced must always have their sharp tip point occlusally. Reversing jaws, positions will result in forward molars tipping and incisor teeth extrusion, which may be used in closing open bites.

Discussion

This article introduces, for the first time, guidelines and instructions to help clinicians insert correct bends in those known-unbendable wires, and orient them in relation to archwire’s lines and imaginary planes to move teeth in the exact prescribed paths of movements.

Bendistal pliers can facilitate the V-bends that can be used to deliver light and consistent forces. Read more about them in this article, “Using V-bends on NiTi wires for nonsurgical correction of Class III malocclusions” here: https://orthopracticeus.com/ce-articles/using-v-bends-niti-wires-nonsurgical-correction-class-iii-malocclusions/

Suhail A. Khouri, DDS, is a Diplomate of the American Board of Orthodontics (1988). He graduated from the orthodontic program at the University of Connecticut in 1980, taught at the University of Connecticut and King Saud University, and later served as a consultant orthodontist at King Faisal Specialist Hospital, Saudi Arabia (1980-1988). He maintained a private practice in Saint Louis, Missouri, from 1991 until he retired in 2015. Dr. Khouri is the inventor and developer of the new Bendistal pliers, (USA patent number 5, 395,236 March, 7, 1995), the first and only pliers that bend and activate the brittle unbendable superplastic archwires. Its clinical use simplified many old orthodontic treatment techniques with highly efficient new ones. He is also the inventor and developer of the Omni pliers (USA, patented 2015), which replace all shapes and functions of the two-paired Bendistal pliers into one pair of pliers. Dr. Khouri is the developer of the new and advanced V-bend technique that simplified many known challenging orthodontic malocclusions. He has published many articles and lectured about this technique in the United States and overseas.

 

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