Advances in lingual appliance technique

30 June, 2011 / Infocus

Lingual orthodontic appliances have been in use for around 40 years. The first lingual orthodontic appliances were developed by two orthodontists working independently in Japan and the United States of America with the first treatments being carried out in the 1970s.

Dr Craven Kurz of the University of California, Los Angeles School of Dentistry, along with his co-workers developed the Kurz/Ormco lingual brackets and during the early 1980s there was an initial surge in the popularity of lingual orthodontics mainly using this system.

Many orthodontists found the new lingual technique difficult to master with a steep learning curve and it failed to take off as imagined. Treatment mechanics were more complex and technically demanding compared to labial appliances. In addition, a high bond failure rate and difficulties accurately rebonding brackets resulted in increased chairside time and poor clinical efficiency. Many clinicians became frustrated with the technique and would often abandon treatment and complete cases with traditional labial appliance systems due to difficulties in finishing cases.

Clinicians were also put off by problems associated with back pain due to the postural challenges of the lingual technique. Around the mid 80s many orthodontists had given up using the technique. From a patient’s perspective lingual appliances were uncomfortable with tongue discomfort and speech problems due to the bulky stock lingual brackets.

In 2004 the Incognito lingual appliance system became available and it was designed to overcome many of the drawbacks associated with previous techniques (Figure 1). Patient comfort was addressed by the use of state of the art CAD/CAM technology allowing customisation of each individual bracket to the patient’s tooth surface. The thickness of the bracket body has been reduced by up to two thirds. Bond failures have been reduced due to the bracket base being larger and customised to fit perfectly to the lingual tooth surface of each individual tooth. The problems associated with finishing cases have been overcome with the use of wire bending robots which very accurately produce customised archwires to the patient’s archform.

A closer look at the Incognito System

The main difference from all other bracket systems is that all the components are custom made for each individual patient. To begin an Incognito therapy it is necessary to take a two-phase PVS impression. High quality impressions are extremely important to ensure a high quality appliance.

The plaster models produced from the impressions are used to prepare an individualised therapeutic setup that is created by cutting the teeth and setting them up in to the ideal position.

Next a high-resolution optical 3D scanner is used to allow non-contact scanning of the therapeutic setup. The result of the scan is a 3D digital representation of the teeth consisting of many thousands of minute triangles that can be documented and processed in the computer.

Specialised CAD/CAM software is used to design and build customised brackets. The process begins with the creation of the bracket base being customised to the lingual surfaces of the patient’s teeth. Because of the extreme accuracy of the scan, the bases mold precisely to the teeth. Large pad surfaces provide greater bond strength and make them easy to place on the teeth for bonding and re-bonding (Figure 2).

After the design of the bracket bases, the appropriate bracket bodies are selected from the digital archive and arranged by the software. The vertical height, angulations and torque are preset into each bracket. In this way the patient’s individual prescription is designed into the brackets (Figure 3).

Once the brackets have been created digitally they are transferred into the real world by using rapid prototyping machines which create wax patterns of the customised brackets. The patterns are then placed in an investment cast, burned out and a dental gold alloy is poured into the cast to create the brackets. After casting, the brackets are polished until they are smooth to ensure high patient comfort (Figure 4). The brackets are bonded to the original malocclusion model and an indirect bonding tray is constructed to aid the orthodontist at bond up (Figures 5 and 6).

The final process is to construct the customised archwires. The wire geometry is calculated by the CAD/CAM program and then sent to a wire bending robot. Each wire in the sequence has the same geometry targeted to the final ideal position of the teeth.

Clinical use of the Incognito appliance

Thanks to the new techniques and technological advances of the Incognito appliance system a new generation of orthodontists have now adopted lingual appliances. The system overcomes many of the problems associated with the lingual appliance technique and it is certainly much easier for the clinician. The clinician should not be fooled into thinking that anyone without the appropriate training can use this system. It is the orthodontist who formulates the treatment plan and is responsible for the final treatment result and the appliance is merely a means of delivering the desired treatment outcome.

In the author’s experience, patient acceptance of the Incognito appliance has been excellent with them adapting quickly to the appliance with very minimal and short-lived interference with speech and minimal discomfort.

Figures 7 and 8 show before and after pictures of a patient who underwent upper arch-only Incognito appliance treatment. The patient is still wearing her appliance in the after photograph. Treatment time was under 12 months and the patient was very happy with the aesthetic improvement.

The appliance system can be used to treat the most complex malocclusions and treatment times are the same as labial appliances. The clinician needs to learn new techniques and appliance adjustments are more complex compared to labial appliances as access is more difficult. The extra effort is worth it as it is professionally very satisfying being able to provide invisible orthodontic treatment to meet your patient’s aesthetic demands.

About the author

Mr Ross Jones, BDS (Hons), BMSc (Hons), MFDS RCS (Edin), M Orth RCS (Edin), MSc, FDS RCS (Edin) is a consultant and specialist in orthodontics. He is available at the Scottish Centre for Excellence in Dentistry for referrals for orthodontic treatment.

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