COMBINING MECHANICS IN LINGUAL ORTHODONTICS

Silvia Geron D.M.D., M.Sc
Dept. of Orthodontics, Tel-Aviv University, Israel

Summery of a paper presented in ESLO 2008 conference in Cannes

www.lingualnews.com Volume 6 No. 1, August 2008

Abstract

The aim of adult orthodontic treatment is to achieve high aesthetic standards, functional and stable occlusion, using the most aesthetic and efficient appliance in a short treatment time.

 The combination of different lingual bracket systems enables  to benefit from the significant advantages introduced in the new bracket systems such as, improved patient comfort, simplified archwire ligation, reduced friction and simplified bracket positioning, based on a thorough understanding of the biomechanics of the lingual technique and the different bracket systems.

A careful biomechanical analysis is required in order to choose the best orthodontic technique, and the most suitable orthodontic appliance for each case. The selection of the proper appliance will yield the straight forward way to obtain programmed dental movements and quick results.

A series of clinical cases demonstrate the strengths of the combined lingual technique. Particular emphasis is given from the perspective of treating complex adult orthodontic cases.

INTRODUCTION
The aim of adult lingual orthodontic treatment is to achieve high dental and facial aesthetic standards and optimal occlusion and function, using the most aesthetic and efficient appliance in the shortest possible treatment time.

To achieve these goals we need a versatile, efficient and effective bracket system.  It should allow good control on tooth position in different movements, torque control, quick frictionless alignment and sliding.  The system should also be easy to use, small and comfortable for the patient, and of course invisible (and cheap, if possible).

Many different lingual brackets have emerged throughout the years, but the most popular lingual bracket was the G7 of Ormco. Although the advantages of G7 in the treatment of deep bite and open bite are well appreciated,  their significant disadvantages cannot be ignore : big, sometimes visible brackets, the hooks causing tongue irritations and speech problems, not to mention the very short interbracket distance, which creates mechanical difficulties during the treatment.

Lately, many new lingual brackets have appeared in the market, and today we have a vast choice of different good brackets. Each shows advantages and disadvantages, but all aim at the same goal: to achieve a correct occlusion within the established aesthetic criteria, while providing improved patients' comfort and easier handling for the orthodontists
 
We are now confronted with the dilemma: how to choose? How to simplify the lingual technique and make it easier?

Each company claims the benefits of its brackets; however, there is still no ideal bracket system that combines all the benefits.

An ideal lingual bracket must have the following characteristics:
 Reduced B-L dimensions 
 Reduced O-G dimension
 Twin design for rotation control
 Easy arch wire insertion
 Easy ligation
 Active spring clip
 Passive ligation- low friction
 Conventional ligation
 SW slot
 Stability of the archwire in slot
 Hooks for ligatures and elastics
 A bite plan

Different cases require different movements and therefore different qualities of the bracket system. For example, if G7 brackets are used to resolve crowding, this may be difficult to handle because of the short interbracket distance, the difficulties in rotations and the patients' discomfort and speech problems. On the other hand, if G7 are used for severe open bite or deep bite cases, the malocclusion can be handled easily because of the bite plan effect and the tongue crib effect.

Instead of searching for the one and only ideal lingual bracket system, it is recommended to combine different brackets and to use different combinations for different malocclusions. The use of more than one technique can significantly enhance treatment efficiency and effectiveness, by using the potential benefits of each technique and gaining the best of all worlds.

Figure 1: STb with .018” slot on incisors and premolar brackets, while G7 .022” slot on the molars provides free sliding of posterior teeth during space closure with reduced frictional resistance

Combining different bracket systems was suggested for the labial technique in several articles:

1. The "Combination Anchorage Technique"- is a combination of the straight-wire technique and the Begg technique. The Begg technique is most effective and easy to apply in the initial stages of treatment to produce quick bite opening, anterior retraction and alignment.  On the other hand, the straight wire technique is more suitable for accurate and controlled movements (1-5).

2. The combination of the straight-wire appliance with Tip-Edge brackets on the canines was suggested by Rocke (6) to overcome over eruption of the incisors and an open bite in the canine/premolar area (Bowing effect) during space closure.  (It may be interesting to adapt this idea to Lingual.)

3. Combining two different slot sizes within the same appliance setup was first proposed by Schudy and Schudy with their bimetric system (7).
Later it was proposed by Gianelly et al with their bidimensional technique (8).
Kurz (9) used a combination of .018 slot brackets for the 3-3 and .022 slot brackets for the buccal segments – premolars and molars, to provide adequate anterior torque control on the maxillary anterior teeth during en masse retraction with the lingual technique.
This combination was also proposed by Geron and Vardimon (10) as one of the six keys to anchorage control with the lingual technique .
Filling the slot and maintaining anterior torque early in treatment is one of the primary benefits of this appliance system.
In the course of retraction, a vector of lingual crown torque or labial root torque is applied. The ability to maintain anterior torque will resist this deleterious movement.

Another advantage of filling the 0.018-inch slot is mandibular incisor control. During space closure in the mandibular arch, or during protraction of the molars, there is a vector that tends to lingualize the anterior teeth. Filling the bracket slots will reserve the position of these teeth and minimize unwanted lingual crown torque.

The use of Class II elastics may strain the position of the mandibular anteriors, and this same mechanism helps to maintain their inclination.

The bidimensional mode allows for the use of a 0.018- inch archwire as the widest diameter, thus creating a 0.04-inch clearance in the 0.022-inch premolar and molar brackets. This differential provides free sliding of posterior teeth during space closure, limiting the frictional resistance, and achieving a more effective space closure system (Figure 1).

Based on these principles, further improvements in treatment mechanics may be achieved by combining a hybrid system with various combinations of conventional brackets and self ligation (Figure 2,3) (11).

Figure 2: Innovation-L self ligating brackets in the premolars provides Secure holding of the archwire during space closure

Self Ligating brackets may have an active spring clip, or Self Ligating passive slide .  For some brackets, the same SL bracket may be active or passive depending on the wire/slot relation. We may combine active or passive SL Brackets with the same slot size for all teeth or differential slot size.

For example, for extraction space closure the anterior brackets could have conventional ligation brackets, or a Self Ligating active clip for 3D control, whereas the posterior teeth could have passive SL brackets to reduce friction for space closure by sliding (Figure 3).

Figure 3: A hybrid and bidimensional system for space closure in a case with normal overbite and increased ovejet. The system includes conventional anterior STb brackets for patient comfort and posterior .022" Quick labial Self Ligating brackets with hooks for frictionless sliding.

The perfect combination for quick space closure will be a hybrid and bidimensional system. The combination of bidimensional system with Self Ligating brackets could give even greater 3D control of the incisors (.018-in slot, possibly with an active clip bracket), and at the same time even greater reduction of friction in the posterior (.022-in slot, possibly with a passive slide bracket) for space closure by sliding and incisor alignment (the wire would pass through the posterior brackets more easily), albeit at the possible loss of some torque and tip control in the buccal segments.

Another example for extraction space closure of a deep bite case, the anterior brackets could have G7 brackets for bite opening, whereas the posterior teeth could have passive Self Ligating brackets to reduce friction for space closure by sliding (Figure 4).

Figure 4: A hybrid and bidimensional system for a deep bite extraction case, including G7 brackets with bite plane, and .022" Quick labial Self Ligating brackets with hooks for frictionless sliding.

Figure 5: Self Ligating brackets on first molar brackets, instead of a convertible tube, if we intend to bond the 2nd molar later.

Even if we do not need reduced friction for space closure we could use Self Ligating brackets on first molar brackets, instead of a convertible tube, if we intend to bond the 2nd molar later. It will be much easier to engage the wire in the molar Self Ligating bracket compared to converting the first molar covertable tube and tying in the first molar with a steel or an elastic ligature (Figure 5).

For open bite cases, we could use the tongue crib effect and the hooks for elastics of the G7 brackets on the incisors, while the posterior teeth could have conventional small brackets or self ligating brackets.

Self Ligating brackets could be used only on teeth distal to extraction sites when closing spaces by sliding, or distal to open coil springs when opening space. The same principle can be applied during protraction: SL on the protracted teeth.

Conclusions:

Different Self Ligating lingual brackets could be used selectively with different conventional lingual brackets, depending on the desired movement.

Selecting the most effective mechanics by combining mechanics improves the efficiency and effectiveness of the bracket system and enhances the consistency and quality of Lingual Orthodontics treatment results.

REFERENCES

1. Fogel MS, Magill JM. The combination technique. Am J Orthod 1963;49:801.

2.Thompson WJ. Modem Begg: a combination of Begg and straight wire appliances. In:

3.Grabor TM, Swain BE editor. Orthodontics: current principles and techniques. St Louis: CV Mosby, 1985:171-89.

4.Thompson WJ. Combination anchorage technique: an update of current mechanics. Am J Orthod 1988;93:363-79.

5. Zuriarrain JL,  et al Our experience in combining mechanics. Am J Orthod Dentofac Orthop 1996;110:575-89.

6. R.Thomas Rocke. Employing Tip-Edge brackets on canines to simplify straight-wire mechanics. American Journal of Orthodontics & Dentofacial Orthopedics October 1994 (Vol. 106, Issue 4, Pages 341-350)

7. Schudy FF, Schudy GF. The bimetric system. Am J Orthod. 1975;67:57–91.

8. Gianelly AA, Bednar JR, Dietz VS. A bidimensional edgewise technique. J Clin Orthod. 1985;19:418–421.

9. Kurz C. The use of lingual appliances for correction of bimaxillary protrusion (four premolars extraction). AJO-DO Volume 1997 Oct (357 - 363).

10. S. Geron, A.D.Vardimon. Six anchorage keys in lingual orthodontic sliding mechanics. World Journal of Orthodontics Vol.4, 2003 (pp. 258-265).

11. Rinchuse D.J., Miles P.G., Self ligating brackets, present and future. Am. J.Orthod. Dentofacial Orthop 2007:132:216-22

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