Components of a loop

Loops consists of horizontal force system, vertical force system, alpha bend, beta bend and helical component. Each loop is constructed with one or more of the above components. Specific component of each loop has been mentioned under the respective loop.^[2]

Classification of loops

Based on configuration

Horizontal loops(e.g. boot loop)

Vertical loops

Combination(T Loop)

Based on purpose of the loop

Leveling and Aligning

Retractione

Multipurpose

Based on presence of helix

Loops without helix(e.g. vertical loop)

Loops with helix(e.g. Helical bulbous loop)

Based on function

Opening loops

Closing loops

Vertical loop([Figure 1])

Vertical loop was in introduced by Robert Strang in 1933. It is constructed with 0.016” SS wire and has a height of 6mm. Vertical loops can be closing or opening loops and can be used for opening or closing spaces and rotating teeth.¹Modifications of vertical loops are^[5]

Double vertical loop used for labial/lingual movement and rotation correction

S loop- similar to vertical loop without undermining occlusal /gingival thrust

Omega loop which gives bodily thrust to the last tooth in the arch

Horizontal loop used for bite opening and easier bracket engagement

Double horizontal loop used for tipping and root movement

Horizontal T loop

Box loop, a combination of horizontal and vertical lever

Torquing loop produces labial or lingual torque

Burstone described the force system of vertical loop in retraction mechanics. Vertical height of 6mm is a typical clinical application as it delivers a force deflection rate of 437g/mm and moment to force ratio to 2.2mm. Moment to force ratio of 2.2mm is too low for uncontrolled tipping.

Moment to force ratio can be increased by increasing the height of the loop. Helix can be added to increase this height, however more than 3 helical turns were not useful. M/F ratio increases linearly as the helix is more apically placed thus further reducing force deflection rate.^[6]

In Beggs mechanotherapy, anterior tooth alignment is accomplished with archwires incorporated with vertical loops. The loops increase the wire span between the teeth and produce a gentler pressure during movement. The looped arch is constructed with a round cuspid hook which rests on the mesial aspect of the cuspid bracket on either side. The loops are then activated to produce overcorrection of rotations, labio-lingual or mesio-distal movement.

Bull loop([Figure 2])

The Bull loop was given by Harry L. Bull in 1951. A sectional steel arch wire made of 0.0215” x 0.025” was used to retract the anteriors. A closed loop in the region of the extraction site of the first bicuspid is activated to open the loop by a millimetre after tying the arches in. A tie-back loop is placed well ahead of the molar tube to activate the arch sufficiently. Dr. William Houghton modified the maxillary sectional arch by adding a small loop, distal to the closing loops for engaging the anterior end of the class II elastics.

An advantage of the use of this loop when used for class II correction in conjunction with class II elastics is that they do not procline the mandibular anteriors since the closing loops restrain this effect.^[7]

Dimensions of the loop for each arch^[8]

Upper bull loop – Height-7mm, wire distal to loop – 18mm, wire mesial to loop -22mm, Lower bull loop – Height-5mm, wire distal to loop – 20mm, wire mesial to loop -28mm

Horizontal loop / Boot loop ([Figure 3])

Boot loop was described by Morris M. Stoner in 1960 and is formed by placing the active legs parallel to the arch wire. Incorporating a horizontal loop allows greater control over the direction of the force.^[5]

The horizontal loop’s principal value is its reduction of force in the vertical plane or occluso-gingival direction, permitting immediate bracket engagement in severely positioned teeth which the operator may want to elevate or depress. It is effective in bite opening. Immediate bracket engagement is possible without excessive force on severely crowded teeth. It is possible to contour the horizontal loop to press against the gingival area to develop a torquing activity on the root; however, clinically has not been found to be very effective. ^[5]

Efficiency of the double Horizontal Loop is best when kept on an individual tooth either above or below the line of occlusion. It can be activated in an occluso-gingival and labio-lingual plane but not in the mesiodistal plane. One loop can be contoured to elevate and the other loop can be contoured to depress, tending to tip the tooth or move the roots.^[5]

Omega loop ([Figure 4])

A variation of the open vertical loop was described by Morris M. Stoner in 1960. It was called so due to its resemblance to the Greek letter omega after which it is named. Its advantage over the open vertical loop lies in its lesser fracture tendency, owing to a more even stress distribution through the curvature of the loop rather than its concentration at the apex. It is commonly used for bodily movement of the root and as a molar stop. ^[5]

A modified omega loop was described to close a maxillary midline diastema by Gandhi et al. by placing two crimpable hooks on the arms of the loop diametrically opposite to each other. An E-chain stretched between the hooks provided the activating force to close the midline diastema.^[9]

Loop ([Figure 5])

Loop was given by Dr Charles J Burstone 1962^[10]

According to Burstone,^[10], ^[11]

TMA wire should be used in construction of T loop.

Additional wire should be placed as far apically as possible to increase the activation moment-to-force ratio.

The loop centricity in the alpha and beta positions affects the rate of change of the moment-to-force ratio.

The large inter-attachment distance between the auxiliary tube on the first molar and the vertical tube of the canine allows sufficient room for the large activations required. In addition, it adds to the accuracy of determining the force system, since small errors in the shape or geometry of the spring will not radically change the forces produced.

Pre-activation bends placed in the loop has been shown in figure 6 and template for T-loop conformation was given by Hoenigl et al,^[12] as shown in figure 7.^[13]

The horizontal activation of the 'T' loop was studied by Koenig et al who found that a 'T' loop activated horizontally by 2 mm had a moment to force ratio which deviated from the reported experimental value by less than 2%.^[14]

Vertical activation of the 'T', 'L', and rectangular loops studied by Vanderby et al.^[15] showed a 'T' loop of 14 mm gingival-horizontal length and activated by 3 mm vertically had moments at the two ends of the loop which were found to be equal almost exactly to the experimental values. The vertical force was found to be higher than the mean experimental value, but within the two standard deviation range.

T loop in continuous arch have vertical segment of equal lengths as shown in figure 8.^[16]

Asymmetric T loop ([Figure 9])

Asymmetric T loop was described by James Hilger in 1992.This loop allows simultaneous bite opening and space closure. It is made of 0.016” X 0.022” TMA or 0.019” X 0.025” TMA wire with 5mm vertical step, 2mm anterior loop, 5mm posterior loop and exaggerated reverse curve of Spee.^[17]

Activation of asymmetric T loop is done by compressing short mesial loop and opening long distal loop.

Double keyhole loop(DKL loop) ([Figure 10])

John Parker of Almeda, California introduced Double keyhole loop (DKL) in Roth treatment mechanics. 0.019” X 0.025” rectangular SS archwireis used for fabrication of DKL. This loop resembles a champagne bottle which is a mixed vertical and horizontal loop.

DKL consists of two symmetrical loops bilaterally near canines that resemble key eyelets. Height of the loop is 7mm and the distance between two loops of the same side is approximately 8 mm.

Indispensable requisites for installation of DKL:

The anterior sector should be diastema free and consolidated with ligature wire to maintain close proximal contact.

Well aligned dental arches with previous arch wire sequence fully expressing torque on each tooth.

Dimension of DKL must be similar to previous rectangular arch wire to allow an easy insertion and perfect sliding of the arch in the slots of the braces.^[18], ^[19], ^[20]

Activation of DKL:

Use of the arch as a spring

Activation by distal traction of the arch

Activation with retro-ligature

Used as an anchorage for auxiliary elements

In posterior sector migration (anchorage loss) type of special cases DKL arch was used as an anchorage for auxiliary elements.

Modification of DKL arch has been used for retraction without torque.^[18]

Rickett’s Canine retraction spring ([Figure 11])

Rickett’s canine retraction spring was described by Robert Rickett in 1976.^[21] The maxillary canine retractor is a double vertical helical T closing loop with extended crossed arms. It is usually fabricated from 0.016”x0.022” SS wire of 70 mm length. It produces a canine retraction force of 50 gm for an activation of about a millimetre. An activation of 3-4 mm is required for individual canine retraction.^[21], ^[22]

In the mandible, the design of the spring is more compact. It is made of 0.016 x 0.016” blue Elgiloy and produces a force of 75 gm for a millimetre of activation. 2-3 mm of activation is required for producing the necessary force.^[21], ^[22]

Opus loop ([Figure 12])

Opus loop was given by Raymond E. Siatkowski in 1977 in study which was a systematic approach to closing loop design for use in continuous arch wires. The design process uses Castigliano's theorem to derive equations for moment-to-forceratio (M/F) in terms of loop geometry. ^[2]

Opus loop is capable of delivering M/F within the range of 8.0-9.1 mm.

Dimensions: 10 mm height, 10 mm length and 0.5 mm radius.It is constructed with 0.016 × 0.022 inch SS wire, 0.018 × 0.025 inch SS wire or 0.017 × 0.025 inch TMA wire. ^[23]

Variations of Opus loops are Opus 90 and Opus 70.

PG retraction spring ([Figure 13])

PG retraction spring was introduced in 1985 by PoulGjessing. The resultant spring design, made from 0.016 x 0.022 inch stainless steel wire and finalized by using a trial-and-error procedure applied to the bench testing set-up. The predominant active element is the ovoid doublehelix loop extending 10 mm apically. The spring is constructed to resist rotational and tipping tendencies during retraction and not to correct rotations and/or extreme deviations in inclination of the canine. Therefore, leveling of the buccal segments must be terminated prior to insertion of the spring.Activation to 140 to 160 grams is obtained by pulling distal to the molar tube until the two sections of thedouble helix are separated 1 mm and is repeated every 4 weeks. Minor rotations of the canine, which may take place during retraction in case of anatomic deviations in root anatomy, are easily corrected with lingual elastics subsequent to retraction. ^[24]

Halazonetis in his study placed pre-activation bends of 15° and 12° on the anterior and posterior legs, respectively. This was followed by activation of loop by 1, 2 and 3 mm. A load deflection of 64 gram force/mm of activation was calculated, which is higher than the 45 gram force/mm reported experimentally. The moment-to-force ratio is high for anterior segment which was ranging from 7 mm to 10.5 mm at 3 mm and 1 mm activation respectively. These values are not as high as those reported by Gjessing. ^[11]

Loop ([Figure 14])

In 1995 Dr. Varun Kalra introduced “K-Loop” appliance for molar distalization in Class II malocclusion, which he claimed to have been developed in accordance to certain biomechanical principles as out lined by Dr. Charles Burstone and has the ability to move the maxillary molars distally with total bodily control which is of great clinical significance The appliance consists of a K-loop to provide the forces and moments and a Nance button for anchorage. It is made of 0.017”x 0.025”TMA wire with each loop 8mm long and 1.5mm wide. Wire is marked mesial to the molar tube distal of premolar bracket, bend is placed 1 mm distal to distal mark and 1 mm mesial to mesial mark. Stop should be well-defined and about 1.5mm long. It is placed with 2mm activation.^[25]

K-SIR arch

The K-SIR arch which stands for Kalra – Simultaneous Intrusion and Retraction was developed by Dr. Varun Kalra. It is a modification of the segmental arch technique as applied to continuous arches. Closed U-loops of 7mm height and 2mm width is fabricated with 0.019”x 0.025” TMA archwire at the sites of extraction. A 90 degree centred V-bend is placed at the level of each U-loop and a 60 degree V-bend located off centred with the shorter arm near the molar tube producing an increased clockwise moment on the 1^st molar thereby augmenting posterior anchorage. A 20 degree anti-rotation bend is used to counter the mesio-lingual rotation of the buccal segments.^[26]

Trial activation reduces the stress build up in the loop and also decreases the severity of the V-bends. It exerts an extrusive moment on the molar which needs to be adequately controlled. This is overcome by the forces of occlusion and mastication. Activation bends are shown in figure 16.^[26]

Its advantages include simplicity in design and fabrication, comfort to the patient and less chances of tissue impingement. As it carries out en-masse retraction it abbreviates orthodontic treatment time compared to conventional edgewise mechanics. Also, this prevents the appearance of an unsightly space distal to the laterals which is seen in individual canine retraction.^[26]

Rectangular loop ([Figure 16])

The rectangular loop described by Drs. Vittorio Cassiafesta and BirteMelsen is a versatile loop which can be used for first, second and third order corrections. Being inserted and held at both ends, it encompasses the statically indeterminate force system. TMA wire is the wire of choice in fabricating a R-loop since wires of varying dimensions can be welded together. Typically, 0.018”/ 0.017” x 0.025” wires are used for the correction of rotated and tipped teeth since they have a large working range. This loop is the most effective in correcting single tooth discrepancies in all planes of space. A good control of the desirable tooth movement along with transference of the undesirable effects to the anchorage unit is noted. A particular advantage of this loop is that round ripping can be minimized with a force system with better accuracy and efficiency. ^[27]

Mushroom loop ([Figure 17])

Pre-fabricated mushroom loop arch-wires were introduced by Drs. Flavio Uribe and Ravindra Nanda in 2003. This looped arch-wire produces an ideal moment to force ratio for translation. Moreover, neither is there any interference of the loop with the gingival tissue nor does it distort readily thereby improving the delivery of orthodontic load. 0.017” x 0.025” β-III Connecticut new arch-wire is used at distances which have been standardized between 26-46 mm with a 2 mm increment. This measurement in millimetre denotes the distances between the distal surfaces of the lateral incisors. ^[28]

Pre-activation of 3mm separation between the legs is done anteriorly along with anchorage reinforcement as necessary. Reactivation of the loop is not done until a closure of 3mm of space closure thus ensuring a constant moment to force ratio is maintained. The same wire is left in place for an additional two visits to ensure correction of axial root inclination by utilizing the residual moments. ^[28]

Snail loop ([Figure 18])

Snail loop was introduced by Dr. Pavankumar Vibhute in 2004. Snail loop is spiral shaped and designed for en masse space closure of the anterior teeth. ^[29]

The snail loop is fashioned from 0.017"x0.025" stainless steel wire by bending a simple omega loop into a spiral shape, which provides the forces and moments. The outer portion of the snail loop is 8mm high and 6mm wide and the inner portion is 6mm high and 3mm wide. ^[29]

Double delta loop ([Figure 19])

The double delta loop serves to close spaces. It is also frequently used for the leveling and integration of the arches. ^[21]

Tear drop loop([Figure 20])

The ideal force applied to achieve movement of the mandibular incisors is approximately 2.60 N. ^[11], ^[30], ^[31]

The springs that best approached this value were the teardrop springs of 6 mm height activated by 0.5 mm, which provided 2.51 N force and the teardrop loop of 8 mm height which was activated 1.0 mm provided a 2.77 N force. The teardrop loops with heights of 7 had values less than 2.60 N, heights of 8 mm had values less than 1.89 and when activated 0.5 mm had values 1.37 N. The teardrop loops with heights of 7 and 8 mm activated 1.0, 1.5, and 2.0 mm had higher forces than the ideal values for mandibular incisor movement.

Bulbous helical loop([Figure 21] )

A helical bulbous loop of height 7.5mm is fabricated at the end of mandibular anchorage preparation of 0.020” x 0.025” arch wire flush against the 2order bends. The helix is wound to the lingual during fabrication. The helical loops are opened by 1mm prior to their insertion which distalizes the 2about molar disalization.

Shoe horn loop ([Figure 22])

Shoe horn loop has been described in Tweed Merrifield appliance. The height of the loop is 8mm. It consists of a long and a short vertical loop.^[32]

Cherry Loop([Figure 23])

Cherry loop was given by Peretta Redento in 2002. It is constructed with 0.017”x 0.025” SS. A large diameter round loop of 8mm width is bent using Rouland plier. Height of the loop is 8-9mm and opens 3-4mm at occlusal end to avoid stress and deformation. Cherry loop is used in molar protraction where it is placed one half distance. The loop is activated in 2 phases, 1.^[33]

Studies on loops have been described in Table 1.