Introduction
The main objective of the active phase of dental treatment is to position the teeth accurately in their correct occluso-gingival placement and mesiodistal angulations while also aligning them in a good arch form and levelling dental units to normal alignment. In order to achieve this, the teeth crowns are placed in labiolingual or buccolingual positions in the alveolus, following the natural contours of a parabolic arch.
In a pre-adjusted appliance, these tooth positions are achieved through the built-in variable thickness of bracket bases and buccal tubes. As for the standard edgewise appliance system, the labiolingual adjustments are accomplished through first-order bends incorporated in the wire.
It is also essential to ensure that the teeth are free from axial rotations. During the incisor retraction and space consolidation phase, the correct labiolingual inclinations or torque of the teeth are accomplished. After space closure, the phase of finishing and detailing of occlusion follows before the bands and brackets are removed.
Steps of the active orthodontic treatment
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Levelling and alignment
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Bite opening
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Space closure
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Torquing and arch coordination and establishment of functional occlusion
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Finishing and detailing
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Deboned and retention
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Follow up
Before commencing the active orthodontic treatment, it is essential to conduct a careful and attentive examination of the dental hard tissues and periodontal health. This examination should include a radiological assessment of teeth suspected of being in unusual locations or affected by periodontal disease. Teeth with severe rotations or those displaced out of the arch require special attention.
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A marked labially/abnormally positioned ( Fig. 55.1 ) or rotated tooth with poor periodontal support would require careful planning not to compromise periodontal health during alignment ( Fig. 55.2 ). A periodontal consult and plan for the management of gingival recession should be integral to the holistic treatment approach.
Figure 55.1 (A–D) A case with severe crowding. Note the gingival recession on the right mandibular canine (Black arrow). Planning the initial alignment mechanics carefully is crucial to avoid compromising periodontal health during alignment.
Figure 55.2 Gingival recession: A periodontal consult and plan for the management of gingival recession should be integral to the holistic treatment approach. (A) shows a patient with a traumatic deep bite and occlusion. Note gingival recession on mandibular central incisors. (B) shows gingival recession in the mandibular left lateral incisor, which requires careful tooth movement planning to avoid proclination.
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Patients with severe bidental protrusion and proclination should be evaluated on a lateral cephalogram to determine the relationship between the roots of incisors with the labial and lingual cortical plates. The alveolar process at the anterior part of the mandible is likely to be thin, which necessitates careful handling of the dental movement ( Figs 55.3 and 55.4 ).
Figure 55.3 Thin labial cortical plates.
(A and B) A patient with bidental, bimaxillary protrusion with thin labial cortical plates in the anterior region of the maxilla and mandible.
Figure 55.4 Pre-treatment evaluation of cortical bone and relationship with teeth.
Parts (A–C) show a patient with bimaxillary protrusion and a vertical growth trend. The incisor area of the mandible has thin labial and lingual cortical bone, which makes it important to institute careful incisor retraction biomechanics to avoid labial root tipping. Additionally, gingival recession on mandibular canines and fractured maxillary central incisors should be noted.
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Similarly, any tooth with marked abnormal mesiolingual root angulation should be evaluated for required modification of conventional archwire design ( Fig. 55.5 ) or modification in the position of the bracket.
Figure 55.5 Pre-treatment evaluation of favourable and unfavourable root angulations.
The root angulation of the right and left mandibular canine tilts mesially, while the root angulation of the right and left maxillary canines is favourable for immediate initiation of canine retraction.
Levelling and alignment
The process of teeth alignment should be initiated only when sufficient space is made available for them on the denture bases. At this stage, clinicians should be aware of precise space requirements, required anchorage and the anchorage savers to be instituted. The planned extractions are carried out, and the patient is re-reviewed for the accuracy of placement of bands and brackets and should there be any interferences must be addressed at this point, before aligning wires are placed in the mouth.
In a non-extraction case, the alignment of the teeth would require one of the following options for the space to be created:
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Proclination of teeth
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Arch expansion
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Proximal recontouring of teeth
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Molar distalisation
In an extraction case, first alignment mechanics should be designed to initiate distal tooth movement of canines into extraction spaces to alleviate crowding. The aligning wires create an occluso-gingival movement of the teeth to level them to correct the marginal ridge relationship with simultaneous correction of rotations.
Highly placed canines and abnormally positioned teeth are moved to occupy their place in the arch. This process of gradual tooth alignment slowly transforms the malocclusion into coordinated arches, which should follow a smooth curve. Efforts are also made to coordinate mandibular dental arch form and width to match the maxillary arch. If not indicated otherwise, care should be taken to maintain inter-canine and inter-molar widths.
The levelling and alignment can be performed either by continuous arches or sectional arches. The sectional arches may be needed in situations of severe crowding or where teeth are placed in aberrant positions.
Sectional arches
Sectional arches may be required to unravel initial crowding where a continuous arch cannot be ligated due to limitations posed by the nature of malocclusion or traumatic bite. Often, such a situation is seen in mandibular canines that need to be moved distally to create arch space for the crowded lateral and central incisors. A closed ‘T-loop’ is fabricated in 0.016 × 0.022 in. stainless steel (SS) or 0.017 × 0.025 in. titanium-molybdenum alloy (TMA) or Elgiloy wire, anchored at first molar, ligated to canine brackets, is gently activated by a distal cinch ( Fig. 55.6 ).
Multiple loops wire in the mandible.
For severe crowding in the maxilla, sectional mechanics followed by piggyback aligner wire and reinforced anchorage. (A) Pre-treatment: This is a case of severe crowding. (B) Sectional loop mechanics was used to align the left maxillary canine and multiple looped round archwires in the lower arch. Maxillary anchorage is reinforced with transpalatal arch (TPA). (C) Levelling is progressing in both arches with round wires. Note that a sectional piggyback NiTi wire is engaged in the left maxillary canine for vertical alignment. The mandibular arch is nearly aligned.
Care should be taken to conserve the anchorage of second premolars and first molars.
Continuous archwire
Shape memory archwire
The initial levelling and alignment of the full arch are usually initiated with light wires (0.014 or 0.016 in.) made of highly resilient, shape memory alloy with a low load-deflection rate. A typical levelling wire extends from the bonded last tooth (first or second molar) on one side to the other side. Initial levelling is often undertaken with smaller dimension wires such as 0.014 in. Nickel titanium strand (NiTi) or flexible multi-strand spiral wires gradually progress for higher size wires up to 0.020-in. steel or rectangular 0.019 × 0.025 in. rigid steel wires. Round Nickel titanium (NiTi) wires work well for the relief of mild to moderate crowding and rotations.
The preformed NiTi wires can be deflected to a large range of tooth movement and yet generate lighter forces. This property is utilised to align blocked out or high labially placed canines. The main disadvantage of such a system is difficulty in controlling the arch form. Wire-bracket friction is a variable factor as the moving teeth displace along the archwire with this approach, making it difficult to accurately predict moment to force (M/F) ratio. Sectional NiTi wires can also be used to align a malpositioned tooth in a piggyback manner for selected teeth where the rest of the dental arch is ligated with a steel wire. With this arrangement, a light continuous force is exerted to bring the displaced tooth into the alignment while reciprocal force is distributed over the anchor teeth through main SS arch wire ( Fig. 55.6 C).
Multiple loop archwires
A multiple loop archwire is comprised of a combination of one or more loops of different designs to suit the malocclusion requirements. The multiple looped wires are tied to brackets to exert moving forces on the tooth roots. This approach is called friction-free-when activated, the archwire loops distort from their original configuration; as the tooth (or teeth) moves, the loop gradually returns to its undistorted (pre-activated) position, delivering the energy stored at the time of activation. Groups of teeth can, therefore, be moved with more accurately defined force systems for more precise anchorage control to achieve treatment goals more readily than methods in which friction plays a role.
A multiple looped archwire is made with 0.016 in. blue Elgiloy or 0.014 in. special or special plus Australian archwire. The author likes to use 0.014–0.016-in. Soft blue Elgiloy wire for making loops owing to wire’s easy formability into different shapes. The bracket prescription tends to express as the treatment progresses, and wires with higher dimensions are gradually used, hence minimising the play between wire and bracket slot ( Fig. 55.7 ).
Levelling and alignment with multiple loop archwires.
(A) Pre-treatment. (B) Multiple loop wires. (C) Treatment progression to attain arch forms and bite opening with rigid wires. Note built in molar stops in maxillary and mandibular arches tied back to molar tubes to prevent proclination while bite opening is in progress. (D) Post debond. Excellent occlusion with good arch forms and normalised anterior and buccal occlusion.
Initial multiple looped archwires are designed to push the canines distally into extraction spaces, thereby leaving enough room for the alignment of the incisors. It is not necessary to engage all the teeth, with full seating of archwires in brackets from the very beginning. Severely displaced teeth may require loose ties in the first wire, and as the treatment progresses, it may be possible to engage the fully seated archwire in the slot. The teeth tend to upright and derotate, crowding is unravelled, the arch form begins to appear, and one can slowly progress to an archwire with higher dimensions and attain an arch form close to the natural shape.
The Elgiloy and SS archwires are required to be heat treated before ligation. The ends of the archwire should be checked for the free slide in buccal tubes.
The assessment of root angulation of canine is an important consideration when choosing and designing the mechanics of its retraction. A malpositioned canine with favourable root angulations (having distally placed root apices) would move faster into extraction spaces. A buccal canine with a distal crown mesial root tip may necessitate a multiple loop wire with appropriate wire bends to correct unfavourable root angulation before it can be moved into extraction space. Such teeth movements are easy to accomplish with looped wires of appropriate designs. It is possible for an orthodontist to create loops with a design that creates the required flexibility and tailored tooth movement in mesiodistal, occluso-gingival and axial (rotational effect) directions.
At the completion of the levelling and alignment stage, all rotations are corrected; good arch form is accomplished with a series of round archwire ranging from 0.016 to 0.022 in. When levelling is completed, a rectangular archwire of 0.019 × 0.025 in. dimensions should be passively seated in the bracket slots. In cases with severe crowding, half to more than half of extraction space may have been utilised by distally moving canines during the relief of the crowding. It is critical that inter-molar and inter-canine widths are maintained, and both arch forms should be coordinated every time a wire is adjusted or substituted with new wire. Pre-treatment study model or the photocopy of the model serves as reference to arch widths.
Loops and helices
The dictionary meaning of a loop is ‘a branch of anything that returns to the main part’. The use of loops in orthodontics can be traced back to 1915, when Robinson made the first loop in the wire. P. R. Begg of Australia extensively used vertical loops for control of rotation, space opening and space closure. He invented special wires with high resiliency and spring back properties for the light wire technique and used them in a variety of ways for making uprighting springs and torquing auxiliaries. Stoner incorporated various loops in edgewise mechanism in the 1960s. However, loops are not in vogue now, probably due to over-dependence on properties of shape memory NiTi wires. The fabrication of looped archwire requires dexterity, consumes significant clinical time in their fabrication, and, moreover, necessitates extra vigilance and care, posing a significant problem in maintaining oral hygiene. The multiple looped archwire also causes discomfort in the oral cavity at least during the initial days after placement. However, multiple loop wires are the most efficient system in the management of severe crowding.
Types of loops
In general, loops can be classified as:
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Simple loops: Loops without helix
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Springs: Loops with a helix
Based on shape ( Fig. 55.8 ), loops can be classified as:
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Vertical loops are primarily used for tooth movement on the horizontal axis. The vertical loops can cause mesiodistal or labiolingual tooth movement.
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Horizontal loops: Mostly used for tooth movement in the vertical axis or occluso-gingival tooth movement.
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The combination of horizontal and vertical loops can be activated to perform tooth displacement in a horizontal and vertical axis and to correct rotations or root uprighting, depending upon the mode of activation.
Commonly used loops and helices.
Multiple loop wires are fabricated with one or more types of loops. Making looped wire is a thoughtful and intricate process of formulating tooth movement and activating the loop mechanics. Loops are made in SS, Elgiloy and TMA wires.
The loops can also be open or closed.
Vertical loop
Open vertical loops are used primarily to open space in a crowded arch. A loop is activated by compressing the legs, which, when assumed in their original positions, move the teeth apart ( Fig. 55.9 ). A coiled base or helix incorporates more wire in the loop, which makes the forces lighter and increases its range of action.
An open vertical loop acts best when compressed.
(A) Open loop generates force to separate the arms when compressed. The open free arm of the safety pin is pressed to be held in a safety loop. (B) The open loop is activated by compressing the vertical arms. (C) Compressed arms tend to open the space.
Double vertical loop
A double vertical loop contoured on each side of a given tooth can be used to move labially or lingually placed tooth into a line of occlusion through the labiolingual spring quality inherent in the horizontal section between the two loops. The double vertical loops can also be used to correct a rotated tooth. The loops are so contoured to affect the desired rotational activity on the brackets ( Fig. 55.10 ).
An open double vertical loop can be used to align a derotated tooth and produce labiolingual alignment.
(A) . Position of open loops. Arrows indicate compression on activation which will help attain arch length/create space required for labial movement. ( B and C ) Labiolingual flexibility in archwire and denoted with possible labial movement in arrow.
Closed vertical loop
A closed vertical loop is used primarily to close a space in the dental arch. The closed loop is activated by pulling the horizontal arm(s) tied to a tooth or a group of teeth ( Fig. 55.11 ). The space closure occurs by frictionless mechanics, that is, the archwire carries the teeth along without sliding. Fig. 55.11 shows a closed vertical loop that can be activated by a pull action. (A) Passive loop (B) Active loop. Part (C) illustrates activation by pull and in the mouth. However, it is important to note that such a loop can produce reciprocal forces that need to be carefully controlled.
It shows a closed vertical loop that can be activated by a pull action.
(A) Passive loops (B) Active loop. Part (C) illustrates activation by pull and in the mouth. However, it is important to note that such a loop can produce reciprocal forces that need to be carefully controlled. In the situation depicted above, anchorage from the second premolar and first molar is utilised to retract the canine.
Horizontal loop
Its incorporation in the wire design permits the force reduction in a vertical or occluso-gingival direction, allowing immediate bracket engagement in situations with a large vertical discrepancy in the positions of neighbouring teeth. The horizontal loop can be designed for a tooth, a group of teeth or a segment of an arch. For example, the horizontal loop can be designed to intrude an extruded incisor, two incisors or six anterior teeth. Another clinical situation can be a need for levelling a segment of the arch by depressing or elevating the anterior or posterior segment and opening the bite.
Double horizontal loop
It is most efficient when working on an individual tooth placed above or below the line of occlusion. It can be most efficiently activated in the occluso-gingival and labiolingual planes. One loop can be contoured to elevate a tooth (segment of an arch), while the second loop can be shaped to depress the tooth (segment of an arch). Its horizontal arm can be used to tip tooth roots or align labial/lingual malpositioned teeth. Double horizontal loops can be prepared in round or rectangular wires.
Omega loop
The omega loop is a variation of the open vertical loop. It is shaped like the Greek letter Ω, and so is the name. It tends to distribute stress more evenly through the curvature of the loop instead of concentrating the stress at the base of the loop. It is used to give the last tooth in the arch a bodily root thrust to enhance molar anchorage ( Fig. 55.12 ).
Omega loop, when activated, generates active root thrust on the molar. It serves as a molar stop and enhances the anchorage.
Combination of vertical and horizontal loop (box loop)
A box loop is a combination of vertical and horizontal arms that are designed in such a manner as to have a short section of wire that can be activated in one or more planes of space. Such a design increases the total amount of effective wire length, which enables greater force reduction capacity and a greater range of action than any other loop. This flexibility permits direct bracket engagement on a severely displaced tooth in the arch. The horizontal arm is inclined to the bracket slot in such a manner that, when engaged, it moves the root of a tooth in a mesial or distal tip. When it is used to tip the root of a tooth, the crown of the tooth to be moved must be so anchored with a neighbouring tooth to prevent its tipping in the opposite direction ( Fig. 55.13 ). The flexible horizontal arm acts to derotate the tooth.
Box loop.
(A) Box loop is activated to the upright mesially inclined root of the right mandibular canine. (B) After correction. Note the change in the axial inclination of the root.
Bent-in stop loop
It is usually made as a molar stop. It is located at the mesial end of the molar tube. Molar stops determine the length of the arch mesial to the first molars on either side. Molar stops are used to maintain or increase arch length by slightly opening the loop or incorporating active loop components. Active loop components tend to procline the anterior teeth. Such a technique is used to align the teeth with mild crowding in non-extraction cases ( Fig. 55.8 ).
Bauschinger’s effect : The inclusion of a loop component in the archwire increases the resiliency of the wire, reduces the force level and increases the range of action by adding arch length in the inter-bracket span. The force of any loop may further be reduced by coiling the wire at the apex one or more times, creating a helix. An open loop is most efficiently activated through compression of the legs. This phenomenon is called the Bauschinger’s effect.
The activity of a loop is dependent upon two types of force built up in the loop: (1) the spring of the legs themselves that act as independent levers and may be activated in any direction, and (2) the activity developed in the curvature at the apex of the loop.
Characteristics of the force system in loop mechanics
For efficient clinical use of loops, the following characteristics of the force system should be kept in mind:
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Force magnitudes and direction.
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Low load-deflection rates.
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Proper moment-to-force (M:F) ratio for producing the desired movement.
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Force constancy that is control over the change in the M:F ratio with respect to deflection.
The type of tooth movement is largely dictated by the ratio M:F generated by the appliance at the attachments. The M:F ratio is the relationship between the applied force and the counterbalancing couple, and its value is the determinant of the expected type of tooth movement ( Table 55.1 ).
TABLE 55.1
Effect of moment to force ratio on tooth movement
| Tooth movement | M:F |
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| Controlled tipping | 7:1 |
| Translational movements | 10:1 |
| Root movement | 12:1 or more |
These ratios are based on the assumptions that the root lengths are 12 mm, alveolar bone condition is normal, axial inclinations of the teeth are normal, the bracket slot to alveolar crest distance is 5 mm and the centre of resistance is located apically at a distance 0.40 times the root length when measured from the alveolar crest to the apex.
Increased loop height greatly raises the M:F ratio. Placing a helix somewhere in the apical portion of the loop increases the M:F ratio further. When a loop is placed closer to one bracket, the M:F ratio increases for the nearer tooth. It is called the V-bend effect.
Bite opening
Correction of deep bite and its maintenance are prerequisites for anterior retraction and space closure. Establishing normal vertical overlap of maxillary anterior teeth is also required, which is a major determinant of functional occlusal relations. Vertical relations of the anterior segment with the lip at rest and at functions determine an individual’s smile.
During retraction of incisors and space closure, there is a further tendency for the incisors to lose their labiolingual inclination and extrude. Hence, a suitable mechanism should be instituted to maintain the normal vertical relations achieved during bite opening. Bite opening is also aimed at placing the maxillary incisors in the correct vertical and labiolingual relationship with lips, which has a considerable influence on the aesthetics and smile line. According to Robert Keim, whatever the primary cause of the deep bite, whether is an infra eruption of the posterior teeth or over eruption of the anterior teeth, the cardinal guide in our decision making process must be the lip-smile line relative to the anterior dentition. If this is not adequately established, the smile resulting from our treatment mechanics may not be acceptable, even if the occlusion is well established.
Several methods can correct deep overbite. The choice of mechanism is guided by the nature of the deep bite, its severity and underlying skeletal relations. In simplicity, bite opening can be achieved by planned anterior intrusion, posterior extrusion or a combination of both.
Methods of deep bite correction can be broadly grouped as:
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Levelling of curve of Spee
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Maxillary incisor intrusion
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Mandibular incisor intrusion
Levelling of the curve of spee
Levelling of the curve of Spee is a major contributor to bite opening. A true intrusion of the mandibular incisors needs to be accomplished where the supra-eruption of the mandibular incisors contributes to the deep bite. A deep bite associated with a low mandibular plane angle, such as in class II division 2 malocclusion, can permit the extrusion of lower molars with the suitable mechanism. Pseudo intrusion/relative intrusion of the mandibular incisors is obtained either by the distal tipping of the molars or allowing mandibular molars to supra-erupt in growing children and flaring of incisors. The mechanics employed are described in the following.
Bite plate
An anterior bite plate is a valuable adjunct to the fixed orthodontic appliance in levelling the curve of Spee in growing children where teeth in the buccal segment erupt to level the deep curve of Spee. , The bite plate, when used judiciously in patients with a low mandibular plane angle, can also initiate some active intrusion of upright lower incisors. However, suppose the inclines of the bite plane and long axis of the mandibular incisors are not favourable. In that case, it may have an adverse effect by causing undue proclination of the mandibular incisors. This mode of therapy for deep bite correction in growing children has been time tested for its effectiveness, but relies heavily on patient compliance ( Fig. 55.14 ).
Bite plate serves as a useful adjunct for levelling the deep curve of Spee.
It allows the eruption of buccal teeth and mild intrusion/labial proclination of the mandibular incisors. (A) Bite plate in situ, (B) expected eruption of buccal teeth. True intrusion of mandibular teeth is expected but negligible or rare; however, mandibular incisors if not taken care may show labial inclination which may not be desired.
Reverse curve of spee wires
A considerable amount of levelling of a curve of Spee in the mandibular arch is obtained while levelling is in progress with fixed appliance therapy. Further, archwire with a reverse curve of Spee (RCS), made of superplastic alloys, such as NiTi, are used to open the bite. These preformed wires made of shape memory alloy deliver gentle intrusion force on incisors and extrusion of the buccal segment. The unwanted effects include difficulties in controlling the proclination of anterior teeth, and poor control of extrusion of the buccal segment and arch form ( Figs 55.15 and 55.16 ).
( A and B ) The levelling curve of Spee with round arches causes labial tipping of incisor teeth. To control labial tipping, the wire must either follow a gentle cinch back or should have molar’s stops tied to the tubes.
Reverse curve of Spee (RCS) wires causes extrusion of the buccal segment. Preformed RCS wires may cause extrusion at unwanted sites as their shape may not always conform to arches/malocclusion in different individuals.
Second-order bends
Mild second-order bends, when employed judiciously, make the distal tip of the molars upright and raise their mesial marginal ridges to open the bite. Tip-back bends at the molars exert intrusive forces at the incisors.
Maxillary and mandibular incisor intrusion
Intrusion with step-up bend
Placement of step bends in the continuous levelling wires and base wires are adjunct to correct a deep overbite. This method of correction combines extrusion of the adjacent cuspids and posterior teeth and perhaps some intrusion of the incisors. Step-up bends are indicated when there is a step between the anterior and posterior occlusal planes in cases with moderate-to-minimal incisor display, and class I occlusion cases. The primary drawback of this approach is the resultant indiscriminate posterior extrusion versus anterior intrusion.
Intrusion arches
The intrusion of the upper and lower incisors, without significant extrusion of the buccal segment, has been described by Ricketts, Burstone and Nanda using continuous intrusion arches as follows:
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Utility arch by R.M. Ricketts
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Intrusion arch by Charles Burstone
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Connecticut intrusion arch (CTA)
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Intrusion with anchorage derived from a mini screw implant (MSI)
The components of the intrusion system are:
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Posterior anchorage unit,
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Anterior segment and
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Vestibular segment.
The buccal segment consists of the first molar and premolar(s), which are so levelled to house rigid stainless steel wire of full dimensions (0.021 × 0.025 in. SS). Transpalatal and translingual arches are used to reinforce the anchorage to counteract reactionary forces generated by the utility arches. The triple buccal tube is required on maxillary molar bands and the double buccal tube on mandibular molar bands for utility arches. The sectional buccal segment wire is housed in the main edgewise tubes, while the utility arch is housed in auxiliary tubes.
The anterior segment consists of four incisors requiring intrusion. Absolute alignment of anterior teeth is not necessary when performing intrusion since minor alignment can happen concomitantly with an intrusion.
Intrusion arches can be made from non-heat-treated 0.016 × 0.016 in. blue Elgiloy wire or 0.017 × 0.025 in. TMA or 0.016 × 0.022 in. TMA wires. Using TMA wires allows the design of the intrusion arch to be simplified, eliminating a need for helices to achieve a low load-deflection rate. It is recommended to avoid placing the wire into the slots as it may lead to an expression of the torque present in the wire. The incisal segment is ligated to the anterior aligning wire or placed incisal to the brackets. Connecticut Intrusion Arches (CTA) are available in preformed wires of highly resilient shape memory NiTi alloys (CNA, beta III nickel-free).
Ricketts’ utility arch
Introduced more than 50 years ago, the utility arch proposed by Dr. R.M. Ricketts is a versatile system of upper and lower intrusion. It can be modified for simultaneous retraction of the anterior teeth or for simultaneous proclination of retroclined teeth as in a class II div 2 situation.
Other contemporary intrusion arches seem to have evolved, keeping the principles of the force system of Ricketts’ utility arch. Better understanding through research on force analysis and the development of TMA wires has helped to devise arches which require fewer activations. The utility arch can be employed to serve different objectives when it is in a passive or active state. The functions of the utility arch are compiled in Table 55.2 .
TABLE 55.2
Indications and uses of passive and active utility arch
| Passive utility arch | Active utility arch can be modified to perform the following functions: |
|---|---|
| It maintains arch length in mixed dentition and prevents worsening of the vertical bite. | Active intrusion of the maxillary and mandibular anterior teeth. |
| It can help to attain proper transverse development of the maxillary dentition by keeping the arch from deleterious influence of the buccinator mechanism. | Intrusion and protraction. This type of movement is required to align and intrude retroclined maxillary central incisors such as in class II division 2 malocclusion. |
| In permanent dentition, it is primarily used to preserve anchorage and maintain the bite. | For anterior intrusion and retraction, during the retraction or at finishing stage. |
Parts of ricketts’ utility arch
Ricketts’ utility arch is made from non-heat-treated 0.016 × 0.016 in. blue Elgiloy wire.
Utility arch consists of two molar segments, buccal bridges, two vertical arms on both sides and an anterior segment. The molar segment is inserted in the buccal tube, and a vertical arm of 4–5 mm emerges in the region of second premolars. The vertical arm follows into a horizontal extension, called the vestibular segment, passing at the level of the marginal gingival edge without touching it. It is followed by the anterior vertical segment somewhat between lateral incisors and canines usually near their contact points. It is 4- to 5-mm long in the mandible and 5–8 mm in the maxilla. The anterior vertical arms of either side are joined by the curved incisal segment ( Figs 55.17 and 55.18 ).
Ricketts’ utility arch. (A) Maxillary arch. (B) Mandibular arch.
The intrusion utility arch is activated by making a 45-degree anchor bend at the molars. Bench et al. recommend the placement of buccal root torque in the mandibular molar region to anchor the roots of the molars in the cortical bone. This type of force produces lingual crown torque that is counter-balanced by placing expansion in the molar region of the utility arch during appliance fabrication. Authors experience about 5mm expansion each side suffices. A slight retraction/lingual force is commonly applied by cinching back the molar segment to alter the force vector, thus preventing undue flaring of incisors while true intrusion is taking place ( Fig. 55.18 B and C; Table 55.2 ).
Retraction and intrusion utility arch in mandible. (A) Utility arch is ligated. (B) A gentle cinch. (C) The archwire can be further activated by an occlusal directed tip back bend (30–45 degrees) in the mesial to the posterior vertical segment.
A retrusion utility arch performs functions of anterior intrusion and retraction simultaneously and contains loops. It is activated by cinching, like the previously described intrusion arch.
A protrusion utility arch protrudes and intrudes the upper and the lower incisors. It is usually used in class II division 2 therapy.
Typically, when activated Ricketts’ utility arch produces 40–80 g of force, which is sufficient to intrude four incisors. However, since the anterior segment of the arch is housed in the brackets of incisors, it is not possible to know the exact amount of force delivered because the force system is statically indeterminate. To counteract the extrusive force on molars, anchorage control with headgear may be required.
A case of class I crowding with excessive gingival display like vertical maxillary excess treated with modified Ricketts’ utility arch is depicted in Fig. 55.19 . Case SG has crowding in both upper and lower arches with anterior maxillary alveolus and incisors are hanging down looking like a vertical maxillary excess. The patient was treated as non extraction case with primary focus on intrusion of maxillary dento-alveolar segment. After levelling the maxillary arch, incisor intrusion was performed with a 0.017 × 0.022 in. TMA, Ricketts’ intrusion arch. As shown in the wire, additional bends to step up were required for central and lateral incisors, with maximum intrusion being effective at central incisors and least on canines.
Effective use of Ricketts’ utility arch.
(A) Case SG. She has crowding in both upper and lower arches with anterior maxillary alveolus and incisors are hanging down looking like a vertical maxillary excess. (B) After levelling the maxillary arch, incisor intrusion was performed with a 0.017 × 0.025 in. TMA, Ricketts’ intrusion arch. As shown in the wire, additional bends to step up were required for central and lateral incisors, with maximum intrusion being effective at central incisors and least on canines. (C) The post-treatment profile and smile photos show marked improvement in the relationship of the upper lip with the maxillary incisors. The marked intrusion of the maxillary incisors has made a major difference in the aesthetic improvement and smile. (D) Pre- and post-treatment extraoral front smile photograph. (E) Pre- and post-treatment cephalograms show improvement in maxillary incisor overbite caused by the intrusion of the maxillary incisors.
The post-treatment profile and smile photos show marked improvement in the relationship of the upper lip with the maxillary incisors. The marked intrusion of the maxillary incisors has made a major difference in the aesthetic improvement and smile.
The second case of class I malocclusion with excessive deep bite treated with utility arch is depicted in Fig. 55.20 . These figures represent the journey of a 17-year-old girl who presented with class I molars but a class II div 2 type pattern of deep overbite with no clearance for placement of brackets on lower incisors. Treatment stages included treatment with 0.017 × 0.025 in. TMA protraction and intrusion utility arch, following which levelling of the upper central incisors lateral incisors was achieved. The lower arch could be bonded after 5 months when the incisors were sufficiently proclined and intruded. Following this, full arch bonding, alignment and levelling continued lighter wires. The case was finished with rigid 0.019 × 0.025 in. stainless steel in both upper and lower arches.
Case DS 17/F. (A.i) Pre-treatment profile and occlusion. (A.ii) She has class I molar relations with div 2 type incisor relations and 100% deep bite. (A.iii) The pre-treatment cephalogram shows div 2 type incisor relations and a 100% deep bite. (A.iv) Pre-treatment OPG. Note the bunching of the roots of the mandibular incisors. (B–D) Treatment progress with a protraction utility arch. (B) A 0.017 × 0.0025 in. TMA protraction and intrusion utility arch was ligated. (C) After levelling the upper central incisors, lateral incisors were also involved in the utility arch. (D) After 5 months, when the incisors were sufficiently proclined and intruded, lower arch bonding was done. (E) Full arch bonding and alignment, as well as levelling, continued on lighter archwires. (F) Final rigid 0.019 × 0.0025 in. stainless steel archwire in both upper and lower arches. Settling of occlusion and full expression of bracket prescription is in progress. (G) Post-treatment profile. (H) Post-treatment occlusion. Note improvement in bite and arch forms. (I) Post-treatment OPG. Note normal root angulation in OPG and de-crowded roots of the mandible incisors (compare with pre-treatment). Flexible wire retainers are provided in maxillary and mandibular arches in canine to canine regions. Flexible spiral wire (FSW) can also be noted in OPG. (J) Pre- and post-treatment lateral profile cephalograms. Note intrusion and proclination of maxillary incisors and proclination of mandibular incisors contributing to bite opening.
Force system of protraction and intrusion utility arch
When a tip back moment is given and utility arch is inserted in molar tube, the anterior end of the utility arch will lie apically in the vestibular region. It has to be moved occlusally to get it inserted in the anterior brackets. Although it appears that intrusion of the anterior teeth will occur but based on the angle of entry into brackets or labiolingual inclination of the incisors, it may increase or decrease the intrusion forces (two couple systems). Activation can also be made at the helix so that the anterior portion of the arch may lie 2–3 mm away from the incisor brackets to cause proclination of the incisors ( Fig. 55.21 ).
The utility arch is a force system used for protraction and intrusion. When inserted into a molar tube, the V bend should be closer to the molars, which will cause the anterior segment to lie apically in the vestibular region. To insert it into the anterior brackets, it needs to be moved occlusal. While it may appear that the anterior teeth will be intruded, the angle of entry into brackets or labiolingual inclination of the incisors can increase or decrease the intrusion forces, resulting in two coupled systems. The helix can also be activated to cause proclination of the incisors. This will make the anterior portion of the arch lie 2–3 mm away from the incisor brackets.
Intrusion arch by burstone
Charles J. Burstone recommended intrusion arch prepared from 0.017 × 0.025 in. TMA wire to generate consistently low forces for a longer duration for the effective intrusion. It is desirable that the forces be generated by a spring mechanism with a low load-deflection ratio in a determinate force system. Therefore, Burstone suggested that intrusive segment of the wire not be seated in the bracket system rather it is tied to an anterior brackets segment in a piggyback fashion. The use of wires made from alloys with high memory and low load-deflection rates produces small increments of deactivation over time and thus reduce the number of reactivation appointments. He suggested continuous and segmented (three piece) designs.
Burstone’s continuous intrusion arch
Burstone’s intrusion arch, when activated, causes extrusion of the buccal segment and intrusion of the anterior segment. Extrusion of the molars is caused by the moment, which is generated in the opposite direction to the intrusive force. The extrusive force magnitude on molars is the same as that of intrusion force. In frontal view, the extrusive force is delivered buccal to the centre of resistance of the maxillary molars which creates a moment that can increase the maxillary arch width. Extrusive forces are in part counteracted by the forces of occlusion generated during chewing. Several modifications in this mechanism have been proposed to maximise anterior intrusion and minimise the extrusion of the molars and unfavourable effects on molar arch width. These are:
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1.
Increasing the size of the buccal segment by splinting the buccal segment in the sectional arch.
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2.
Keeping the intrusive force on the anterior segment as low as possible.
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3.
Counteracting the extrusive force on the buccal segment. A high-pull headgear (which is not required when forces are kept low except in high angle cases where anchorage control is difficult) can be used. Vertical molar control can be attained with enhanced anchorage supported with mini screw implant (MSI), thus eliminating a need for extraoral anchorage.
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4.
A passive transpalatal arch is used to maintain inter-molar distance or counteract the contraction forces on the arch width.
It is not clear that what amount of force is considered optimal for the effective intrusion of the anterior segment. Commonly, 10–20 g of force/tooth is advocated for maxillary anterior intrusion. ,
Fig. 55.22 shows the Burstone’s continuous intrusion arch in the mouth for intrusion of maxillary incisors. Fig. 55.23.i shows its graphic representation.
