Comparison between sliding and loops mechanics. Its influence on torque and vertical problems

Pablo Echarri, DDS
President of ESLO

www.lingualnews.com, Volume 1, Number 2 - March 2003

The aim of this article is to analyze the differences between sliding and loop/non-sliding mechanics from the point of view of their influence on torque and vertical control.

The results were that while the sliding mechanics is more comfortable for a patient and easier for an orthodontist, the loops mechanics provides a better vertical and incisors torque control.

In order to use most of the times the sliding mechanics, it's very important to achieve the complete leveling of the curve of Spee, the molars and bicuspids occlusal contacts, the complete correction of the overbite and the overcorrection of the incisors torque.

 Keywords: Lingual orthodontics. Sliding vs. loops mechanics.

INTRODUCTION
A survey of my clinical cases reveals that 40% of my lingual cases were treated using an extraction-based treatment modality. Of these, 85% of were administered sliding mechanics to resolve their malocclusions.

Comparison of sliding and loop mechanics reveals the advantages and disadvantages of each technique. Sliding mechanics present with several advantages, namely, its chair-side simplicity for the orthodontist, patient comfort, and ability to achieve desired results. However, this method is not without its disadvantages. Sliding mechanics produce circumstances that result in loss of incisor torque control, as well as deepening of the overbite which occurs due to weak vertical control.

Alternatively, non-sliding/loop mechanics can be used to achieve space closure. Here too are inherent advantages and disadvantages. The advantages of this approach include good control of incisor torque and the vertical dimension. The weaknesses of loop mechanics are that it requires time-consuming wire bending, clinically difficult archwire activation, and tends to cause patient discomfort due to wire irritation.

Abstract:

The lingual technique protocol
The lingual technique protocol followed and recommended by myself includes several ordered steps. Firstly, each patient undergoes Alignment, Leveling, and correction of the rotations (A.L.R.). To achieve this .016" NiTi archwire or .017" x .017" Copper NiTi archwire with Scott's ligatures to correct the rotated teeth are used. This step may require the initial distalization of the cuspids, especially when the case presents anterior crowding and incisor protrusion not indicated.

The ensuing step it that of third order, or torque, control. In this instance .0175" x .075" TMA archwire with a tip-back and a toe-out compensation curves are utilized.

The third step in the lingual treatment protocol, following establishment of torque control and now that the roots are properly oriented (in spongy bone), is the correction of vertical discrepancies. With things organized in this manner, teeth can be extruded or intruded while avoiding the cortical bone. In order to maintain the roots inside the spongy bone it is very important to control their torque during the vertical movements.

With regard to intrusion of incisors, fixed lingual orthodontics has an advantage over labial techniques. The location of lingual brackets in relation to the center of resistance of each incisor permits direction of the line of force nearer to it. Therefore, torque is easier to maintain in this instance, as opposed to attempting the same movement with labial brackets. Here, torque is constantly increasing during intrusion because of the same biomechanical considerations.

An additional factor which must be weighed against the diagnostic information is mechanism by which vertical control will be expressed. In other words, whether this (bite opening) will occur due to incisor intrusion or buccal segment extrusion.

In order to decide the most appropriate way to undertake any such vertical correction several things must be taken into account. Firstly, that buccal segment extrusion necessarily increases the vertical dimension. Secondly, that any such correction in the lower jaw causes rotation of the occlusal plane in a clockwise direction with the opposite occurring when undertaken in the upper jaw. Finally, the lip-to-tooth relationships should also be determined (i.e. incisor show at rest and smiling etc.).

The forth step in the lingual treatment protocol concerns with space closure. Once the curve of Spee is leveled, the overbite corrected and the molar and bicuspid occlusal contacts established, space closure can proceed. The most useful archwires for this purpose are the .016" x .022" SS or the .017" x .025" TMA.

Because lingual appliances are an esthetic consideration, anterior tooth retraction is undertaken in an "en masse" fashion. Simultaneous retraction of incisors and cuspids carries with it an increased anchorage requirement, and need for vertical control. These requirements can be achieved in several ways with differing archwire configurations depending on the individual situation.

-For example, a .016" x .022 SS "mushroom" wire with tip-back and toe-out curves together with an elastic chain for sliding mechanics (Fig 1) provides the minimum of the overbite and incisors control. On the other hand, it is the most comfortable archwire for a patient and the easiest archwire for an orthodontist.

 
Fig 1: Minimum control of the vertical bowing effect : .016" x .022" stainless steel archwire with tip-back curve and toe-in curve and elastic chain.

Another option is a .017" x .025" TMA with an "I" closing loop (Fig 2). This provides a medium amount of control of the overbite and incisor torque, however it is slightly less comfortable than the previous example and requires additional manipulation by the orthodontist. This archwire is activated by a circle loop.

Fig 2: Medium control of the vertical bowing effect: .017" x .025" TMA archwire with "I" closing loop and circle and tip-back curve and toe-in curve.

A .016 x .022" SS with a "T" closing loop archwire (Fig 3) provides excellent control of overbite and incisor torque, but is least comfortable for the patient and it is the most complicated archwire for the orthodontist to prepare. The "T" loop permits intra-oral activation of incisor torque and/or overbite control by the use of a three-prong plier on the horizontal arm of the "T" loop.

Fig 3: Maximum control of the vertical bowing effect: .016" x .022" Stainless Steel archwire with "T" closing loop and omega loop and tip-back curve and toe-in curve. Activating the horizontal arm or the "T" loop, you can get less or more intrusion and torque control.

Should sliding mechanics be our method of choice, it is imperative to establish certain occlusal relationships before initiating space closure. Firstly, the curve of Spee must be leveled. This is followed by the need to over-correct the incisors torque, and correction of the overbite.

Having achieved the above dental movement the final step of the lingual treatment protocol can be carried out. This step is referred to as the finishing and detailing step. Here, it is recommended that a .016" SS archwire with omega loops be used. This arch wire can be detailed with 1st and 2nd order compensation bends if .

Case presentation
A 19-year-old female patient showing a class I malocclusion with crowding, transmigration between upper right lateral incisor and canine, persistence of the upper right deciduous canine and shape malformation of the upper left lateral incisor (fig 4).

Fig 4: Initial intraoral pictures

 

Treatment included extractions of upper right deciduous canine and right and left lateral incisors and the extractions of the lower right and left second bicuspids (Fig 5). Aesthetic pontics were used after the extractions (Fig 6).

Fig 5: Intraoral pictures after lower expansion and extractions

Fig 6: Aesthetic pontic in the maxillary arch

After Lower expansion with a lingual expansion archwire,Ormco lingual bracket Kurz # 7 for the upper and lower arch were placed.

Wire sequence in the maxillary arch (Fig 7):
.016" NiTi for initial alignment.
.016" SS with elastic chain for space redistribution.
.016" NiTi for definitive alignment.
.0175" x .0175" TMA upper archwire.
.016" x .022" SS upper archwire, sliding mechanics.
.016" SS finishing archwire.

Fig 7: Treatment of maxillary arch:
a-.016" SS upper archwire with elastic chain for space redistribution.
b - .016" NiTi upper archwire.
c- .016" x .022" SS upper archwire. Sliding mechanics.

Wire sequence in the mandibular arch (Fig 8):
.016" NiTi lower archwire.
.0175" x .0175" TMA lower archwire.
.016" x .022" SS lower archwire, sliding mechanics.
.016" SS finishing archwire.

Fig 8: Treatment of mndibular arch:
a - .016" NiTi lower archwire.
b - .0175" x .0175" TMA lower archwire.
c - .016" x .022" SS lower archwire. Sliding mechanics.

Final results are presented in Figure 9.

Fig. 9 Final Intraoral Pictures

CONCLUSIONS
The steps of the lingual treatment that we recommend are:
1. A.L.R.
2. Establishment of torque (Note: incisor torque is to be individualized per tooth and per patient).
3. Correction of the overbite, leveling of the curve of Spee.
4. Space closure.
5. Finishing and detailing.
If sliding mechanics are to be the treatment modality of choice, it becomes very important to establish all the corrected intermediate occlusal relationships prior to anterior tooth retraction and space closure. Meaning, that leveling of the curve of Spee, correcting the overbite, incisor torque buccal segment occlusion, etc.must all be accomplished successfully before the overjet is reduced. If the bowing effect or loss of torque is noticed during treatment, all current mechanics must be discontinued and the orthodontist must return to steps 2 and 3 before continuing with space closure. It should be kept in mind that while sliding mechanics are more comfortable for the patient and clinically simpler for the orthodontist, loop mechanics provide better vertical and incisors torque control.

www.lingualnews.com 
Adult and Lingual Orthodontics
EDITORS:
Dr. Silvia Geron D.M.D., M.Sc
Dr. Rafi Romano D.M.D., M.Sc
Dr. Pablo Echarri D.M.D., M.Sc