Dental Asia May/June 2020

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Clinical Feature Rationale of the new technique This technique was actually inspired by the ability of Bendistal Pliers to place lasting bends and activate tied super elastic archwires intraorally. Resiliency of super elastic wires provided light force delivery and allowed bending tied archwires without breaking adjacent brackets. Also the stability of bends ensures consistency of force delivery over the long range of activation those wires are famous for. The key to the success of this technique is its simple clinical applicability, its convenience and time savings, besides enabling orthodontists to customise the number and locations of the intrusive V-bends on tied archwires. Mechanical considerations of the V-bends 1. It is well known that a V-bend on any orthodontic wire creates two moments equal in magnitude and opposite in directions acting on teeth in both sides of that bend (Fig. 4a). The labially directed moment acting on teeth segment anterior to the V-bend is counteracted by an equal and posteriorly directed moment (side effect) on teeth segment posterior to that bend. Analysing those moments to the couple of forces causing them, we see intrusion of the furthest teeth on both sides of the V-bend, and extrusion of teeth closest to that bend (Fig. 4b). The intrusion effect and the extrusion side effect resulting from this V-bend technique work favourably to open the deep overbite. Fig. 4a: Diagram showing analysis of the force system created by V-bends located between canine and first premolar. To bring the system into equilibrium, anterior moment M1 must be equal to posterior moment M2 Fig. 4b: Shows the intrusion and extrusion effects of both moments acting on tooth segments located on both sides of the bend 2. The apically directed forces applied through facial brackets of anterior teeth intrude them and cause them to flare because the force line passes facial to their centre of resistance creating a labially directed moment. Such flaring can be controlled with elastomeric power chain extending from one upper molar to the other. 3. In maxillary first premolar extraction patients, posterior segment consisting of first molars and second premolars provides an anchorage of eight roots, to intrude the six roots of the anterior teeth segment. Posterior teeth anchorage can be further strengthened by adding both maxillary second molars that increase number of anchor roots to 14, if minimal side effect is indicated. The anterior teeth intrusion is elicited by the vertical component of force of the anterior clockwise moment causing the bite to open. Clinician can decide whether to prevent or take advantage of the extrusive side effect on teeth close to both sides of the V-bend that help opening the deep overbite as well in Fig. 4. 4. Although intrusion of the furthest molars of posterior segments may be an unwelcome side effect 23 , it is advantageous since the apically-directed force acting buccally to molar’s centre of resistance intrudes their buccal cusps and extrudes their lingual cusps. This very side effect becomes a favourable and indispensable step to disengage upper and lower molar cusps that simplifies cross-bite correction by routine bend adjustments. It actually constitutes the core of the rationale for another technique to correct cross bites. Clinical technique and wire sequence Traditional intrusive appliance designs and springs made of stainless-steel wires required long prefabrication time, frequent adjustments, and high patient cooperation over long treatment times. Although V-bends on stainless steel wires were already known to intrude teeth, their relative stiffness and short range of activation limited their efficiency and clinical application. Bendistal Pliers provides a clinically simple way of placing V-bends on titanium archwires to ensure light and consistent intrusive force delivery. To master this technique, orthodontists must have a good background in creating the bite opening force system through placing V-bends that incidentally conform to segmental formats. This technique can be started as early as when the initial small-sized 0.016” NiTi wire finishes its sole role in preliminary teeth alignment. Instead of discarding this wire, placing V-bends on it distal to both canines will rejuvenate this wire, Fig. 5a: Right intraoral view of 100% severe overbite before treatment Fig. 5b: During treatment with the intrusive V-Bends in both dental arches 34 DENTAL ASIA MAY / JUNE <strong>2020</strong>
Clinical Feature Fig. 5c: Post-treatment result and take its performance to a much higher level as shown in Fig. 4. Once the bite opens enough to allow mandibular incisor bonding, a similar small-sized NiTi wire is tied in to align mandibular teeth and possibly start early intrusive bends on mandibular archwire. Then the light magnitude of the intrusive force on anterior teeth can be increased according to case severity, by upgrading the wire size to a thicker, rectangular one (Fig. 5). If overbites extend more that 100%, greater force is required to intrude anterior teeth. V-bends on larger-sized rectangular NiTi wires (0.016”X0.022”) deliver a relatively greater consistent force that is still tolerable by patients, yet not so stiff as to break the neighbouring tooth brackets As the mandibular teeth align and the mandibular curve of Spee starts to flatten, replace the initial wire with a 0.016”X0.022” NiTi archwire to get a greater force magnitude by placing similar V-bends in the same locations on it. Monitor the case for few months until the overbite opens. In cooperative patients, overbite is corrected in about six months. In later stages of treatment, if greater force is required, stainless steel rectangular wire may be used with similar V bends to maintain results. A very gentle or incomplete squeeze of the plier jaws is adequate to activate stainless steel wires to deliver a greater intrusive force without breaking adjacent brackets. Patients who display severe skeletal overbites (150% or more) will benefit from acrylic bite plates that will allow early and simultaneous mandibular incisor bonding and commencement of intrusion mechanics on both dental arches (Fig. 6). Simultaneous bonding both arches shortens bite opening time. The same wire sequence and activation is followed in mandibular arch as that in the maxillary. Fig. 6a: Intraoral right views before treatment showing severe overbite of Class II Division 2 Fig. 6b: During treatment with the arrows pointing at locations of the intrusive disengaging V-bends Fig. 6c: Post-treatment after four-bicuspid extraction Once overbite opens enough to allow mandibular incisors bonding, remove the bite plate and leave the active wires for few more months until the normal 1-2mm overbite relation is restored. Intrusive wires should not be left in mouth unsupervised for long durations to avoid unnecessary over treatment. At this stage clinician can reposition mandibular incisor brackets more incisally where needed, especially in cases where the brackets were placed gingivally to avoid occlusal interference. This step flattens mandibular curve of Spee and facilitates restoring and maintaining the normal overbite relation with just tying a straight wire. Rectangular finishing NiTi or stainless steel archwires without bends are recommended for this purpose. Should the need for additional bite opening develop during the finishing stage, half-squeeze bends on stainless steel wires or full squeezes on finishing NiTi wires will allow additional correction. Fig. 7a: Before treatment of a complicated case and two upper unerupted canines, with initial 016” round NiTi archwires with multiple V-bends to disengage the interlocking incisors. Notice brackets were placed in any available areas to speed up the disengagement of incisors Fig. 7b: During treatment before erupting the canines Fig. 7c: Post-treatment front intraoral view Dealing with severe skeletal overbite that is complicated by excessive skeletal overjet in Class II Division 1 patients, there is usually an adequate space allowing mandibular incisors bonding with or sometimes, without bite plate. Despite the severity of such cases, simultaneous commencement of bite-opening mechanics on maxillary and mandibular arches along with maxillary anterior teeth retraction that should have MAY / JUNE <strong>2020</strong> DENTAL ASIA 35
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Dental Asia May/June 2020

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