In an excerpt from his book, Lingual Orthodontics: The Truly Invisible Orthodontics*, lingual scholar Gilbert takes a look at the practical side of this technique.

Advantages of the Lingual Technique Over the Labial

1. Invisibility: Notwithstanding the quality of plastic or ceramic apparatus, it is indisputable that the only apparatus impossible to detect by the human eye are those not fitted to the labial surface of the teeth. It has been claimed that the transparent apparatus manufactured from acetates are useful in the carrying out of complete orthodontic treatments. However their limitations are evident (Figure 1).
2. Exclusivity: We live in an extremely competitive society, where the alternatives are to offer an excellent service, with innovations and various options, or to be resigned to severely lowering costs to remain in the market. The first option allows the orthodontist a more relaxed practice, with a better income and without detriment to his or her quality of life.

Alfredo Gilbert, DDS, MS

3. No damage to the labial surface: It is very common that patients without adequate dental hygiene may suffer from decalcification and/or stains of the enamel. Located on the labial surface, these could lead to future complications. It is also necessary to recognize that the use and later removal of orthodontic glues may damage the surfaces on which they are applied (Figure 2).
4. Fewer incidences of caries: Those patients with lingual apparatus have a significantly greater flow of saliva than those with labial apparatus, a benefit that decreases the risk of caries during treatment. Saliva is not only an acid neutralizer during mastication.¹ Saliva also plays an important role in the prevention of caries by controlling pH balance and facilitating remineralization of the enamel.

Saliva is rich in phosphates and calcium, and it expedites remineralization in early decay lesions. This has been documented and is evident upon reviewing the effects that salivary dysfunction has on the incidence of caries and their sites of prevalence.

Figure 1: On the left, the true invisibility of lingual brackets. On the right, the semi-invisibility of ceramic brackets.

Figure 2: The removal of orthodontic adhesive can damage the labial surfaces of the teeth.

5. Anchorage control: One of the most important issues that the orthodontist must deal with in order to achieve treatments of the best quality is the correct managing of the dental anchorage.² Although some cases require maximum anchorage (that is, an attempt to avoid completely the mesialization of the posterior teeth), other cases require a certain forward movement of the posterior segment; in still other cases it is necessary that the molars and premolars are moved forward as much as they possibly can be.

Furthermore, control of vertical anchoring is essential because extrusion of the molars leads to mandible rotation in a clockwise manner, creating a Class II relation with open bite. The use of a bite plane in the lingual technique facilitates the mechanics in cases of deep bite, but may provoke opening of the bite in the medial and posterior segments upon eliminating the vertical and sagittal anchorage of the occlusion. Because of this, the most important factor to be considered in the first stage of treatment is the maintenance of the anchorage and of the occlusion in the medial and posterior parts of the mouth.

This may be obtained in two ways:

• Cementing the braces as close as possible to the gum line, which may prevent opening of the bite in the posterior section; or
• "Compensating the posterior open bite by fitting glass ionomer to the occlusal face of the inferior molars.

In the lingual technique, it is common to close extraction spaces en masse. This is done as much for aesthetic reasons as for biomechanical convenience. Naturally, the closing of large segments compromises the anchorage. However, there are different methods to augment the anchorage, such as the use of elastics, Goshgarian, buccal segments, closing with or without friction, and passive anchorage blocks, etc.

6. Biomechanics³: One of the great advantages of the lingual technique over the labial is the proximity of the center of resistance made possible by the fitting of the apparatus on the lingual face of the teeth. Of the six possible planes to be considered (horizontal, vertical, and sagittal in each maxilla), in five we find that the center of resistance is located closer to the point of application of force in the lingual technique than in the labial. In only one plane (the sagittal in the superior arch) we find greater proximity in the labial technique than in the lingual. Notwithstanding this exception, the moments of force are considerably reduced in the lingual technique with respect to the labial, giving as a result purer and more controlled movements.

Figure 3: In some lingual patients, the tongue suffers irritation while it adapts itself to its new position.

Disadvantages of the Lingual Technique

1. Speech difficulties: Patients with lingual braces commonly experience speech difficulties, but these are usually overcome within a week. Some patients require training for the pronunciation of particular sounds; but it seems that the tongue possesses a natural capacity to adapt itself to its new position in such a way that improvement is rapid and complete.
2. Chewing problems: The posterior teeth cease to occlude for a period of 1 to 2 months, a time during which the patient experiences an uncomfortable lessening of his or her ability to chew food. In some cases, to minimize this sensation, the fitting of bite planes on the occlusal face of the posterior teeth is recommended. The key to the design of lingual apparatus was the addition of a bite plane to the anterosuperior teeth, which transformed the tearing forces produced by the inferior incisors into compressive forces in the apical and labial directions. One obstacle to the completion of many lingual orthodontic cases is that the patient at some stage bites the braces. The braces with lids cause a large part of this problem, but I have found that these cases can be completed by simply removing the lids of the relevant braces in the final stage of treatment. I will discuss this point in my speech at the ALOA meeting in Denver next May. In certain patients, the tongue also suffers irritations while it adapts itself to its new restricted position (Figure 3).
3. Technical difficulties: Orthodontists wishing to practice lingual orthodontics must be sufficiently qualified in order to successfully deal with all the idiosyncrasies of the technique. More chairtime must be invested in each patient, and the orthodontist must have the wire-folding ability that each case requires.

Fitting Lingual Apparatus

There are two essential concepts concerning the fitting of lingual apparatus:

1. Lingual apparatus are fitted in an indirect way. Irregularities of the lingual surface and difficulty of access to the surface make placement directly into the patient's mouth impossible. To circumvent these difficulties, different systems have been designed in which the first step is the fitting of the braces to a model of the patient's mouth.
2. Lingual braces must be transferred to the mouth of the patient, a step in which various systems and materials may be used. Later in the article, I will discuss the different systems of positioning and transference that are used in lingual orthodontics.

Fundamental Differences Between the Lingual and Labial Techniques

Mechanically speaking, the main difference between the techniques lies in the point of application of the force. With the one exception noted previously, the application point is closer to the center of resistance of the tooth in the lingual technique than in the labial. As demonstrated by Scuzzo and Takemoto,⁴ this means that forces applied at the lingual face of the teeth produce smaller moments of force than are produced by the application of forces at the vestibular face of the teeth. Consequently, the lingual orthodontist has to deal with fewer complications involving uncontrolled dental movements.

The Bite Plane

The effect of the compressive forces over the bony surface is the physiological resorption of bone in the incisive area, which translates to an intrusion exerting less of 100 mg of force. (Swallowing 2,000 times per day provides approximately the same magnitude of force.) The first occasion in which a bite plane was used was in 1976, and since then the apparatus has formed one of the cornerstones of lingual philosophy.

Levers in Lingual Orthodontics

Integration of the concepts of occlusion particular to any dentistry specialty is essential for adequate management of the treatment. Any implement that may interfere in the relation between the mandible and the cranium upon modifying the articular eminence/condyle communion possesses the potential to convert class 3 occlusal levers⁵ to class 1 levers. The latter are too mechanically powerful and tend to deteriorate the system.

Because of this, whenever a lingual orthodontic treatment is implemented and the bite is raised to avoid obstruction to the occlusion that the apparatus would otherwise entail, the operator must adjust the occlusion in such a way that the convenient class 3 levers are not abandoned.

The most effective option for this purpose consists of the implementation of bite planes in the posterior dental segment.

Apparatus Positioning Systems in Lingual Orthodontics

The Silam System

Silvia Geron, DMD, MSc, designed a positioning system with the Roth prescription that makes use of individual guides, specific for each of the superior teeth. The procedure is as follows:

With the aid of a compass, the widest upper tooth (usually the canine) is chosen, and its measurements are recorded. The brace of the chosen tooth is placed in the corresponding guide, which is opened to the number of millimeters determined by the compass. The whole is transferred to the model and positioned according to the reading of the guide. All of the remaining guides are opened to the measurement of the widest tooth (with the aim of standardizing the positions of the teeth from inside out) and are adjusted, with the respective braces, to the corresponding teeth. The braces are bonded, and the guides are removed.

The CLASS System

This positioning system is realized from a dental setup in the laboratory, following the prescription ordered by the orthodontist. Upon carrying out the dental repositioning of the model, the positions of the three orders are obtained, as well as standardization of the positions from inside out.

What this setup achieves is to convert the original system of 0º to a straight-wire system from the beginning of the treatment. It is a rather exact system, with the disadvantage that it requires a laboratory to possess positioning apparatus.

The TARG System

The TARG system consists of the utilization of an apparatus that has different blades (one for each tooth) that may be angled as desired by the operator. Information is transferred from the labial face of the model to the lingual face (as in the Silam system). The apparatus consists of an inclined plate on which the model is placed—an arrangement that permits adjustment of the blades in accordance with the prescription intended for each tooth—and also a height meter to achieve the desired height for each tooth. It is possible to consider the TARG system providing in some sense a "virtual" setup, because, without selecting the model, the teeth are positioned in a predetermined position.

The RAY-SET System

An even more sophisticated virtual setup is that provided by the Ray-Set system. Thanks to the utilization of a goniometry and a rotary plate, it is possible to determine, without cutting the teeth, the exact position subsequent to the treatment, thus avoiding practically all of the compensatory folding during treatment. The positions of the Ray-Set system are additionally verified by virtue of a luminous beam from a laser source. This facilitates an adequate positioning, based on the location of the Q point, which consequently perfectly reproduces positions of the second and third order. An inverse cemented guide is used to standardize the buccolingual width.

The HIRO System

In this system, a real setup is carried out, since the teeth are cut from the model and are rearranged into the "ideal" position. Subsequently, an arch is manufactured from steel of caliber 0.018 x 0.025 and is tied to the braces. This arch is carried to the model where the braces are cemented. The resin base acts as a filling material in order to convert the braces into a guiding arch. The Hiro system permits the positioning of the braces inside the orthodontist's office without resorting to external laboratories.

Alfredo Gilbert, DDS, MS, is a guest professor of lingual orthodontics at the Hospital Infantil du Mexico Federico Gomez and the academic coordinator of lingual orthodontics at the Facultad de Estudios Superiores at the Zaragoza campus of the Universidad Nacional Autónoma de México. He can be reached at .

*Lingual Orthodontics: The Truly Invisible Orthodontics. Mexico:Trillas; 2008.

References

1. Stephan M. The role of diet, fluoride and saliva in caries prevention. J Indian Soc Ped Prev Dent. 1997;15:109-113.
2. Graber TM. Biomechanical principles of the orthodontic movement of teeth. Types of Anchorage. Orthodontics, Principles and Practice. Interamericana;1985.
3. Proffitt WR. Biomechanics and mechanics. In: Contemporary Orthodontics. St Louis: The C.V. Mosby Co; 1986:227-269.
4. Scuzzo G, Takemoto K. Invisible orthodontics. In: Biomechanics and Comparative Biomechanics. Chicago: Quintessence Books; 2003.
5. Geber A, Steinhardt G. Dental Occlusion and the Temporomandibular Joint. 1st ed. Chicago: Quintessence Publishing Co Inc; 1990.