Lingual technique

Lingual technique

 1.Introduction 

Since their birth, multi-bracket techniques have continued to evolve, allowing orthodontists to treat the majority of malocclusions. The major drawback until then was the unsightly side of the devices, which was difficult for patients, mainly adults, to accept. 

These same patients are currently involved in choosing their orthodontic treatment and insist on having a good quality of life during treatment. Most undergo this treatment primarily for aesthetic reasons, and given the influence of the acceptability of the appliance on social judgment, the choice is in favor of non-visible devices. (33% to 62% of adults refuse treatment with a visible appliance). 

This demand for “invisible orthodontics” has led orthodontists to develop an aesthetic system such as lingual or aligners. 

 2. Definition 

Multi-bracket orthodontic technique based on bonding orthodontic brackets to the inner surface of the teeth.

Lingual orthodontics was born in the 70s, under the impetus of Dr FUJITA and Dr KURTZ.

 3. History 

In 1976, Fujita and Kurtz filed patents for lingual brackets, the first in Japan and the second in the United States. 🡪 Difficulties: bonding brackets, controlling movements.

In 1984, the Ormco laboratory developed a machine called the TARG, which allowed the positioning of brackets to be optimized. After a period of euphoria, in 1985, many practitioners abandoned this technique which was too imprecise and it was no longer used except by a few diehards.

One of the major difficulties was to assess all the necessary bends on the arch in order to align the contact points. The first development was to do without these bends by adding between the intrados of the bracket and the tooth thicknesses of glue intended to compensate for the different thicknesses of the teeth.

This system had its limits because the thickness, sometimes very significant, of the glue pads made the fasteners very uncomfortable and reduced their resistance to detachment.

The next development was to do away with this glue pad and circumvent the problem of very complicated arch bends on the lingual surfaces. To achieve this, in 1999 Dirk Wiechmann developed a technique using a robot to manufacture custom arches.

Thanks to this contribution, he proposed attachments much closer to the teeth , therefore more comfortable and more resistant to detachment.

 From that day on, the thickness differences were reflected on the wire in the form of first-order deformation.

The last weak point was the attachment itself: not very precise, it sometimes caused unwanted movements and the finishes then became very difficult to achieve. 

To overcome this last obstacle, in 2002 Dirk Wiechmann and the Top Service laboratory developed a custom-made bracket with a precision that was then unmatched. This bracket would give rise to the Incognito® technique ( individualized lingual bracket system).

4.Means of processing 

4.1. Lingual attachments: 

  4.1.1. The choice of lingual brackets 

Several options are available to prescribers:

• Ribbonwise attachments (Ribbon VH) in which the wire is inserted:
        – vertically in the anterior part, which offers great ease in correcting rotations and improves torque control (Fig.1);
        – horizontally in the posterior area, which increases tip control, especially in cases of extractions (Fig.2). These attachments are used in 90% of cases.
• Edgewise (edge) fasteners which take the shape of classic fasteners.

As in vestibular, there are conventional brackets and self-ligating brackets.

Fig. 1          Fig. 2

We can divide the fasteners into two categories: 

• Prefabricated lingual brackets (fig. 3): The volume of the bracket, its base and the adaptation to several groups of teeth have evolved over time.

(fig. 3) 

• Individualized lingual brackets by CAD/CAM (fig. 6): the bracket will be manufactured individually, using a laboratory procedure that is carried out according to the following steps: 

• The use of a virtual model (a 3D optical scanner) on which the design of the brackets is carried out in relation to the anatomy of each tooth (fig. 4);
• Digital construction of the bracket body from a digital library (fig 5);
• Exporting virtual brackets to a conversion device: by a CNC (computerized numerical control) system, 3D printer producing castable models. (These “virtual” brackets will be materialized in a
  first step in wax brackets, then by a lost wax casting procedure, in individualized gold brackets (a gold-palladium alloy)

Lingual technique

Lingual technique

The advantage of these individualized attachments is the custom adaptation of each base, which allows attachments to be bonded with complete peace of mind to natural or prosthetic teeth regardless of their shape or size. This feature is very advantageous in older adults for whom it is not uncommon to encounter very atypical crowns. Conversely, it is just as interesting in the treatment of children, in particular to adapt the bases to second molars that are not very developed. In cases of crowding with teeth in high rotation, the lingual surface is sometimes difficult to access. Custom manufacturing allows all teeth to be bonded, even those that are difficult to access, provided that the available surface represents at least 50% of the total surface of the palatal surface.

 4.1.2. Positioning of lingual brackets 

The direct positioning of the brackets in the mouth presents a great difficulty, it was necessary to turn to the indirect technique which is done in 2 stages: 

• Positioning of the brackets in the laboratory using the TARG ;
• Transfer of these brackets into the mouth using a transfer tray.

Three different materials are available for the manufacture of the gutter (fig. 7):

Lingual technique

                     (fig. 7)

Hard silicone in Lutésil® Mémosil Bioplast Gutter

3. Bonding of lingual brackets:

• Preparation of dental surfaces and setting up of the surgical  field : The palatal surfaces are sandblasted with 50 µm aluminum oxide. This operation is essential if we want to obtain a quality bond.
• Etch with 37% orthophosphoric acid for 30 seconds then rinse and dry;
• Indirect bonding using chemical or photopolymerizable techniques;
• Aesthetic caches (fig. 8).

 (fig. 8)

Lingual technique 

 4.2. The choice of arcs: 

The archwires are manufactured by a robot. Through the bracket manufacturing software, the robot knows exactly the position of the grooves on the set-up. It needs to know the horizontal plane, the anteroposterior position of each slot and its position in the first order relative to the slot preceding it. The robot is able to bend Copper-NiTi®, steel and TMA wires.

Several materials are offered depending on the treatment phase:

• Leveling phase: Copper-Niti ^® .016 then .016×.022;
• Working phase: steel wires .016×.022 or .016×.024;
• Finishing phase: TMA. 

• The .0175×.0175 for first and second order corrections, 
• The .0182×.0182 for torque corrections.

5. Advantages and disadvantages:
6. Advantage : 

Invisibility of the device.

2. Disadvantages

• Technical difficulty;
• Significant time spent in the chair;
• Speech gene;
• Difficult hygiene;
• Limited power supply;
• Taking off a bracket.

 6. Conclusion

Lingual orthodontics took its first steps thirty years ago and the demand for this type of treatment continues to grow. Currently, the lingual technique is very popular with patients. However, it is a fact that lingual treatment is among the most difficult to perform for the practitioner. This is why every practitioner who wishes to use it must apply themselves rigorously to master it and be able to benefit from it.

Lingual technique