Uses of the Vertical Slot in Orthodontic Brackets

Many orthodontists have discovered the utility of a simple, vertically positioned square hole in an orthodontic bracket. The vertical slot, or V-slot, permits the simple addition of a variety of useful auxiliaries and biomechanical adjuncts (Fig. 1). As Gianelly once said in a personal communication, "I don't understand why you wouldn't want a vertical slot in your bracket, whatever bracket you choose; it's free."

Unfortunately, little has been published specifically on the use of V-slots, other than in the Begg system¹ and Gianelly's Bidimensional technique.² Although some clinicians might assume that the addition of a V-slot would raise the profile of the orthodontic bracket, thus increasing patient discomfort, recent design improvements have resulted in a lower profile in both standard and self-ligating brackets.^3,4 This article describes various applications of the V-slot in an edgewise bracket system.

Uprighting Springs

Uprighting springs are typically used with V-slot single brackets or Begg brackets to upright the roots of tipped teeth. In the edgewise technique, these springs provide a reversible and versatile method of controlling anchorage by increasing resistance to sliding.⁵ The crown of the tooth is tipped until the opposite internal angles of the bracket slot contact the archwire, creating a binding effect (Fig. 2).

Uprighting springs are a less costly and invasive alternative to temporary anchorage devices or site-specific surgical procedures such as corticotomy or microperforation of the cortical bone.

Gianelly's Bidimensional protocol is especially suited to Class II extraction cases, in which lower posterior teeth need to be protracted into the extraction spaces.⁶ The protraction is accomplished with nickel titanium closed-coil springs while the position of the anterior teeth is maintained, thus actually losing or "burning" posterior anchorage (Fig. 3).

Class II elastics are worn on one side and Class III elastics on the opposite side of the arch, with tooth movement expedited by the uprighting springs.

Rotating Springs

Rotating springs made of round wire can also be used with V-slots to correct individual dental rotations¹ (Fig. 6). This not only avoids the limitations of passive self-ligating brackets, but precludes the need for counter-rotational Lewis wings on narrow brackets. Since superelastic wire materials have diminished the interbracket-distance advantage of single brackets, small twin brackets with V-slots appear to provide more versatility and control.

The Compliance+ spring^* was designed for two different applications. Its force is derived from a combination with intermaxillary Class II, Class III, or delta (triangular) elastics. If the elastic hook of the Compliance+ spring is adjusted to protrude slightly into the buccal tissue, it will cause minor soft-tissue irritation that can be alleviated simply by wearing the elastics (Fig. 7). The spring auxiliary slides onto the main archwire before the leg of the spring is inserted into the V-slot. The archwire must then be tied into the bracket with a stainless steel ligature to prevent it from becoming dislodged by the spring. When the Compliance+ spring is placed over a round base archwire, it produces single-tooth labial root torque. This is often useful after a palatally impacted canine has been moved into the arch, though the root will still require labial movement. The Compliance+ spring can also provide labial root torque for lingually positioned upper or lower lateral incisor roots. To avoid generating unwanted labial torque, the spring must be used with a rectangular base archwire.

Power Arms, T-Pins, and Elastic Hooks

Orthodontic patients frequently complain about protruding ball hooks, which can be annoying in terms of appearance, comfort, and oral hygiene. V-slots permit the addition of power arms, T-pins, or elastic hooks on any individual teeth (Fig. 8).

The patient is less likely to wear elastics in the wrong configuration (such as Class II instead of Class III) when these hooks are added only where forces are required, and they can easily be removed after use. The clinician is able to prescribe intermaxillary elastics to be worn from the maxillary lateral incisors instead of the canines ("long Class II"), from the lower second premolars ("short Class II"), or even in zig-zag or "spaghetti" configurations on nearly every tooth to improve final intercuspation. Individual hooks eliminate the inconvenience of fumbling with soldered or crimpable hooks.

Longer power arms can be inserted into V-slots to allow the application of orthodontic forces closer to the center of resistance of the tooth for more efficient movement. The power arms will also lie closer to the facial surface of the tooth than a ball hook would be, thus reducing the rotational potential of retraction forces. For instance, in an extraction case, maximum anchorage for canine or en masse anterior retraction may be derived from a miniscrew inserted mesial to the first molars. If forces were applied from the miniscrew directly to the canine bracket, the consequent rotational moment might cause more crown tipping (Fig. 9A). If the force is instead applied to a power arm inserted in the V-slot of the canine bracket, a more translatory movement is produced (Fig. 9B).

Power pins, T-pins, and elastic hooks can also act as substitutes for labor-intensive soldered or crimpable hooks in patients undergoing orthognathic surgery (Fig. 10). Power pins are easily inserted for temporary ligation of a splint during surgery, or for elastic wear after surgery, and can be removed when no longer needed.

V-Tie Ligation

V-slots seem indispensable if for no other purpose than to allow insertion of ligature wires or elastic threads for correction of severely rotated or displaced teeth (Fig. 11). If the popular low-friction mechanics are desired, the least friction and widest interbracket distance for initial alignment would be obtained from a loosely tied stainless steel ligature, especially if it is inserted through a V-slot and simply looped around the archwire ("sling tie" or "V-tie").

The V-slot is particularly useful when an ectopic or blocked-out tooth cannot be tied in conventionally, or when a tooth is significantly misaligned after a bracket has been lost between appointments. Instead of applying excessive force to fully engage the archwire into the bracket, the clinician can pass a stainless steel ligature wire or elastic thread through the V-slot and around the archwire. As the ligature wire is reactivated or the thread is replaced at each appointment, the tooth will gradually be drawn back into the arch (Fig. 12). The V-tie may thus avoid the need to step back in archwire dimension, potentially reducing treatment time and expense.

Overlay Wires

It is not always possible to bracket second molars early, since they may not erupt until later in treatment when orthodontic mechanics have progressed to large dimension rectangular wires. Buccally erupting second molars are especially challenging if the first-molar brackets are not convertible or self-ligating. In that situation, the clinician is often required to return to undersize or more elastic wires to "gather up" the displaced second molars, with a consequent loss of three-dimensional control throughout the dental arch. A possible solution is to keep the larger rectangular wire from first molar to first molar and add an overlay wire such as .014" superelastic nickel titanium from the second molars, ligated with stainless steel ligatures through the V-slots of the premolars and canines⁸ (Fig. 13). Similarly, a V-tied overlay wire can also be added to the base archwire to facilitate the addition of a second expanded or reverse-curve wire for leveling during alignment with a small-diameter base wire.

Alternative Methods

As an alternative to V-slots, Binder developed uprighting and rotating springs for use with standard and preadjusted edgewise brackets.⁹ A different method proposed by Jain involved a modification of Begg uprighting springs for preadjusted edgewise brackets.¹⁰ Although the mechanical principles are similar to those described here, these systems require greater manual skills and can be utilized only with uprighting and rotating springs.

Conclusion

The use of V-slots makes any edgewise technique more efficient and versatile, while making the appliance more comfortable for the patient.