Arch wire sequencing in Orthdontics

 

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Arch sequencing depends on :

1-  Archwire Types

2-  Archwire Functions

3-  Archwire Sequencing according to cases (where different situations requires sequences )

4-  Pain associated with Archwire placement and activation 

INTRODUCTION

       A successful orthodontic therapy depends not only on manual skills and knowledge of treatment steps but also on knowledge and choice of materials used. One of the major components of fixed orthodontic therapy is the choice of wires. Orthodontic wires are defined as devices comprising a wire conforming to the alveolar or dental arch, which is used as an anchorage for correcting irregularities in the position of teeth . Therefore, the aim of the this assignment  was to focus on the differences in the features of wires as well as their working sequence according to the treatment plan.

 

1-  Archwire Types:

 

1-   ARCHWIRE MATERIALS

 

a-    Precious Metal Alloy  :  Used in the first half of twentieth centuary

·         Gold alloy with platinum, palladium, copper were used.

 Advantages :

·         High ductility 

• Inert nature and corrosion resistance - so did not form toxic products with saliva

 • Variable stiffness- by heat treatment 

• High resilience and 

• Ease of soldering

Disadvantages :

·         Elastic force delivery much less 

• Greater cost compared to other base metal wires 

• Have minimal use currently

 b-    Stainless Steel

·         Used for most orthodontic wires 

• Low cost • Excellent formability 

• Good mechanical properties 

• Can be soldered and welded for the fabrication of complex appliances Orthodontic wires are of the “18-8” austenitic type, containing approximately 18% chromium and 8% nickel 36

·         Resistance to corrosion The chromium gets oxidized È Impermeable, corrosion resistant layer. (passivation)

·         Heated to 400-900 °C Chromium combines with carbon Chromium carbide. Corrosion resistance of steel is reduced. (Sensitization)

 c-    Cobalt- Chromium Alloy Originally used for watch springs

·         Composition: – Cobalt – 40-45% – Chromium – 15-22% – Nickel – for strength and ductility – Iron, molybdenum, tungsten and titanium to form stable carbides and enhance hardenability.

·         Supplied in a softer form Shaping of wire done in softer form Heat treatment (500 0C) Wires get hardened (equivalent to SS)

·         Disappeared by the end of 20th centuary • Additional cost • Extra set up for the heat treatment to obtain optimal properties

 

 

a-    Nickel Titanium Alloy  Useful during the initial orthodontic alignment.

·         Can apply a light force over a large range of activations. • Nitinol (Ni, nickel; Ti, titanium; NOL, Naval Ordnance Laboratory) – first Nickel Titanium alloy developed for space program 

·         Shape memory • Ability of material to remember its original shape after being plastically deformed. Certain shape is set at an elevated temperature When the alloy is cooled it can be transitionally deformed Heated enough to regain the austenitic structure Origional shape is restored 

·         Reversible strain wire can withstand due to martensite- austenitic phase transition • Transition to martensitic in response to stress

 

b-     B- Titanium Alloy In orthodontic use about two decades ago by Burstone and Goldberg

 The commercial name for this wire is TMA, which represents “titanium-molybdenum alloy

  Offers a highly desirable combination of strength, springiness and formability.

·         Excellent choice for auxiliary springs and for intermediate and finishing archwires

·          Especially rectangular wires for the late stages of edgewise treatment 

 

c-    Gold wires 

d-    Australian heat treated wires

e-    Alpha Titanium wires

f-     Copper Niti wires

g-    Ceramic wires

1-   Size and Shape :

 

Based on cross section

 

1. Round

2. Square

3. Rectangular

4. Multistranded 

Shapes of arch wires

 

Round wires

·         Initial and intermediate stages of treatment to correct crowding, level the arch, open a bite, and close spaces.

 

 Square or rectangular wires

·       Final stages of treatment to position the crown and root in the correct maxillary and mandibular relationship

   Wire Size • Specified in thousands of an inch Eg, .016 inch =16 mil 16 mil → 16/4 = 04 → 0.4 mm 40 mil → 40/4 = 10 → 1.0 mm 

2-Archwire Functions

The functions of the archwires, in sequential order, include:

 

1. Elimination of rotations

 

2. Development of arch form ( where patient’s original arch form should be preserved following the

anatomy of the basal bone in order to avoid relapse )

 

3. Leveling of the arches

 

4. Control of torque

 

Archwires take time to fully express their potential. The orthodontist must allow the archwires the time necessary to express their full potential before moving on to the next archwire. This is especially true during elimination of rotations with the initial archwire. the importance of allowing the wires to complete their objectives,. However, for the arch wires to fully express their desired effects, the orthodontist must always ensure that the archwire is fully engaged in the bracket slot.

  Categories :

The very complex subject of archwires can be understood more easily at a basic, clinical level by learning about the four distinct categories they fall into: 

 

Phase I: Initial Light Round Wires

In the initial Ni-Ti light round wire phase, archwires are carefully selected to minimize binding between the "tube" of the bracket and the archwire. This allows sliding of the teeth and brackets along the wire as they start to level and align.

Binding and friction in a conventional mechanical system comes from the ligature pushing on the wire and the seating of archwire against the base of the slot. There is also the binding created by the deflection of the archwire against the sides of the bracket slots in crowded cases.

In recent years, many clinicians have started cases placing large dimension rectangular Ni-Ti archwires with the intent of controlling torque to minimize the dumping of the incisors as teeth level and align.the intent of the initial light round archwires is to apply just enough force to stimulate cellular activity without crushing the vascular supply in the periodontium. This has been defined as staying in the "optimal force zone" or biozone. If the appropriate force is applied, the muscles of the face and lips give a "lip bumper" effect on the incisors, minimizing anterior tipping.

The intent of the initial archwire is not to remove all of the rotations, but to align teeth and bracket slots just enough to move to the second phase of archwire progression. This is best accomplished by taking advantage of using a small dimension archwire in the large lumen of the bracket. An analogy of this phase of treatment is a car being driven on both sides of a curving highway to straighten out the bends in the road. This same principle of archwire and tube helps minimize the force and binding friction.

To summarize: The initial phase starts tooth movement, rotation control, leveling, aligning, arch form, and prepares for the second phase of archwire sequencing.

 

Phase II: High-Technology Edgewise Wires

The second, or high-tech edgewise phase, This phase starts working on torque, root angulations and levels, completes rotation control, continues arch form development, consolidates space in the anterior segments, and prepares for the third phase of archwire sequencing. It is critically important to take a panorex and evaluate root and bracket position before proceeding to the major mechanics phase of treatment.

Phase III: Major Mechanics

The third, or major mechanics phase of archwire sequencing, is the working phase of treatment. This includes posterior space closure, anteroposterior dental correction and adjusting buccolingual discrepancies. Stainless steel archwires are primarily used to maintain vertical and buccolingual control during this major mechanical phase of treatment.

Phase IV: Finishing

The fourth phase is the finishing and detailing phase of archwire sequencing. If adjustments and torque requirements are minimal, the working archwire can be used to complete treatment. If moderate bends and torque are required, it is strongly recommended to use edgewise TMA. This gentle archwire makes finishing easy for both patient and clinician.

 

CLINICAL IMPLICATION PRINCIPLES IN THE CHOICE OF ARCHWIRES

 

·         Move freely within the brackets.

·         At least 2 mil clearance between the archwire and the bracket is needed

·         4 mil clearance is desirable

·         Tightly fit rectangular, the position of the root apex could be affected, normally should be avoided.

 

ARCHWIRE FABRICATION

•       Dental arch form varies among individuals

•      Basic principle -> the patient's original arch form should be preserved

3-Archwire Sequencing

 

Nonextraction archwire sequence: Maxillary arch (Mild to Moderate crowding )

 

Initial

Flexible round (0.014 or 0.016-inch NiTi). These archwires are bent back distal to the molars (“cinched” back).

Purpose: These archwires are used to correct rotations, initiate leveling, and develop arch form.

Duration:1 to 3 months. The patient is examined at 4- to 6-week intervals to tie any rotations and to ensure that the archwire is fully engaged.

 

Transitional

Intermediate (0.016-inch SS to 0.016 × 0.022-inch SS). Omega loops are placed mesial to the terminal molar band and tied back. Reverse curves are formed in these wires for treatment of deep bite.

Purpose: These archwires are intended to complete any rotation correction, continue leveling, provide torque control, and develop arch form. If any spaces are present, these are closed with 0.016-inch SS archwire and elastomeric chain, from molar to molar. 

Duration:  2 to 4 months at 5- to 6-week intervals.

 

Finishing

Stiff rectangular (0.017 × 0.025-inch SS). This wire is always used with omega loops—tied back.

Purpose. This archwire finalizes leveling, torque, and arch form.

Duration. Through the end of treatment. Appointments are scheduled as needed to correct the final occlusion.

Nonextraction archwire sequence: Mandibular arch (Mild to Moderate crowding )

 

Initial

Flexible rectangular (0.014 or 0.016- inch NiTi,). The archwire does not have to be tied or cinched back.

 

Purpose. The archwire is intended to correct rotations, initiate leveling.

 

Duration. 1 to 3 months.  The first goal is to achieve good archwire engagement in the brackets. When this is difficult to accomplish, interproximal enamel reduction with a 0.016-inch NiTi may be necessary. Bend back (cinch back ) may be needed to control the faring of the lower anterior teeth .

 

Transitional

Intermediate (0.016 × 0.022-inch SS or 0.017 × 0.025-inch SS). More than one archwire may be required. Omega loops are placed in these archwires and tied back. Reverse curves are formed in these wires for treatment of deep bite.

 

Purpose. These archwires provide minor rotation correction, continued leveling, arch form development, and torque control.

 

Duration. 3 to 6 months.

 

Finishing

Stiff rectangular (0.017 × 0.025-inch SS). These finishing archwires always have omega loops placed and tied back. The final amount of reverse curve is dependent on the patient’s degree of overbite.

 

Purpose. These wires are used to finalize leveling, torque, and arch form.

 

Duration. Through the end of treatment. Appointments are scheduled as needed for correction of the final occlusion. This is a high-stiffness archwire and must therefore be precise in its final form, which will be replicated intraorally.

Extraction archwire sequence: Maxillary arch & Mandibular arch (severe crowding ) :

 

 

Flexible (initial) archwire

Maxillary arch: 0.012- inch  NiTi

Mandibular arch: 0.012 – inch NiTi

 

Transitional (intermediate) archwire

Maxillary arch: 0.016-inch SS

Mandibular arch:  0.016 inch SS

 

Closing archwire

Maxillary arch: 0.017 × 0.025-inch SS with closing loops; 0.017 × 0.025-inch T-loops

Mandibular arch: 0.016 × 0.022-inch SS with closing loops

 

Stiff (finishing) archwire

Maxillary arch: 0.017 × 0.025-inch SS

Mandibular arch: 0.017 × 0.025-inch SS

4-Pain associated with Archwire placement and activation :

Pain associated with initial archwire placement has been previously researched. Jones (1984) reported that pain is experienced by the majority of patients 4 hours after archwire placement, which will peak at 24 hours and then decline. Various authors, who performed the same research in other racial and ethnic groups, confirmed these findings (Ngan et al., 1989, 1994; Scheurer et al., 1996; Firestone et al., 1999; Erdinç and Dinçer, 2004; Polat et al., 2005). Jones and Chan (1992b) stated that pain from archwire placement can be worse in some patients and could even be more than that experienced after tooth extraction. They observed a diurnal variation in pain experienced by patients—with evening and nights showing the highest scores. The pain will usually last for 2–3 days and will gradually decrease in its intensity by fifth or sixth day (Jones and Chan, 1992a, b).

Comparing various archwires to determine differences in pain perception showed no statistically significant results. No difference in the intensity, prevalence, or duration of pain between different archwires was found (Jones and Richmond, 1985; Fernandes et al., 1998; Erdinç and Dinçer, 2004). Erdinç and Dinçer (2004), in agreement with others (Ngan et al., 1989, 1994; Scheurer et al., 1996), found that patients reported more pain experience in anterior than in posterior teeth because of the differences in root surface area, increased involvement of anterior teeth during levelling, and greater use of anterior teeth for biting. Fernandes et al. (1998) reported that after 11 hours of force application, a higher pain perception was experienced in the lower than in the upper arch.

A literature search regarding pain perception following archwire activation resulted in few publications. Gianelly and Goldman (1971) stated that the conditioned and/or nociceptive reflexes elicited as a result of orthodontic archwire activation often leads to avoidance of chewing hard foods by the patients. Smith et al. (1984) and Goldreich et al. (1994), through different experiments, evaluated the effect of orthodontic archwire activation on the masseter muscle through EMG activity. They observed a reduction in masseter muscle activity and attributed this to the noxious stimuli emulating from the periodontal membrane or paradental receptors triggering a reflex mechanism, which caused inhibition of jaw-closing muscles (EMG activity during induced pain has been shown to increase when jaw-closing muscles act as antagonists, Lund et al., 1983). In brief, both archwire placement as well as activation will cause pain and might affect dietary habits as well as the daily life activities of patients.

If