IntroductionThe last decade has brought a revolution to the world of dentistry in the form of digital technology. Software has allowed the modeling and simulation of clinical situations, while computer controlled mills enable anatomical restorations cut from new materials like ultra-tough zirconia. Similarly, Internet connectivity has dramatically increased the speed and depth of communication between the dental professional and laboratory, while further facilitating low-cost file storage of digital records that can be retrieved instantaneously across global networks.

Digital technology has enabled the creation of the Incognito™ Appliance System by allowing the design and manufacture of brackets individually customized to each tooth and coordinated across the arch to set the precise custom arch form. However, until recently, all Incognito System cases have relied on the traditional wax and plaster diagnostic setup to create the target position for the teeth. Placed in the hands of skilled technicians, this time-tested approach physically replicates the dentition, and allows the technician to craft the desired target occlusion.

The precision of the Incognito setup is critical, since studies show the Incognito System is proven to deliver the target result for patients.1,2 As the world moves toward digital technologies, big questions loomed for Incognito System development: Could software be created to deliver a virtual setup meeting these exacting standards? And, could the additional benefits of enhanced communication and digital storage be realized for Incognito System customers?

In a multi-year effort, 3M software and setup experts collaborated to build digital setup software capable of consistently producing digital setups of Incognito System quality. While sophisticated 3D software tools for creating setups are increasingly available, a key challenge faced the team – how to create an Incognito System setup digitally that had the same quality as the wax and plaster setups that had established Incognito as the lingual custom appliance of choice. The path to success lay in creating a tightly knit team of software experts and Incognito System setup technicians to replicate the physical setup process using state-of-the-art software algorithms.

The steps to produce a wax/plaster setup and digital setup are similar. Both start with high-quality impressions which are converted into a positive plaster model. The teeth are identified and marked. This is followed by segmenting the teeth from the gingiva. For plaster, the teeth are physically cut from the model. In software, sophisticated algorithms identify the tooth margin and make a digital cut. One of the first benefits realized in the digital world is the ability to ‘undo’ a mistake, while a mistake with physical tooth separation results in a re-pour and restart of the process (Figure 1A-D).

James D. Hansen,

PhD is Vice President

of Research and

Development for

3M Unitek. He has

been working in

dental and orthodontic product development

at 3M for 21 years. His academic training

is in Material Science, with a PhD from

Northwestern University and a BS from the

University of Minnesota.

Creating Digital Setups for the Incognito™ Appliance Systemby James D. Hansen and Ralf Paehl, 3M Unitek

Ralf Paehl

leads the R&D

department at

TOP-Service for

Lingualtechnik

GmbH, a 3M Unitek

company (Bad Essen, Germany). With

his group he develops both mechanical

and software solutions for custom lingual

orthodontics. He received his diploma

in aeronautical engineering in 1992 in

Braunschweig, Germany, and joined

TOP-Service in 2001.

Once separated and marked, the alignment process begins within each arch. Malleable wax is used to support the plaster teeth as they are arranged in the prescribed arch. Digital teeth are manipulated in 3D virtual space with a mouse or joystick (Figure 2A-B).

1A

2A

2B 4A 4B

1B

1C

1D

3

Figure 1A-D: Manual and Digital separation performed by the setup technician.

Figure 2A-B: Setup technician positioning teeth manually and digitally.

Figure 4A-B: Physical and Digital Articulator used by the setup technician.

Figure 3: Overlay view as seen by the setup technician.

Measurements from the maloccluded model are made to determine changes in intercuspid and intermolar width in the setup. Physical templates are used to align the occlusal plane and prescribed arch form in the wax and plaster setup. The toolset in the digital world includes all of the traditional tools, but new ones as well, like overlay views and geometric tools for precisely tailoring the arch form (Figure 3).

Bringing the two arches together to form the final occlusion is one of the greatest challenges. In both worlds, the arches are mounted in an articulator. In the physical world, the occlusion is adjusted by feel as the two arches are brought together. In software, high-speed computation now allows this to be simulated by detecting contact between teeth, and then iteratively adjusting the position of teeth (Figure 4A-B).

However, the software only gives a first approximation; the final occlusion is manually obtained by adjusting the teeth and using the cross section tools and occlusal maps to optimize the contacts. These new digital tools allow the Incognito™ Appliance System technician to view and adjust the final occlusion via cross sections that are not available in the physical world (Figure 5).

6B

6D

6A

6C

7

5

Figure 5: Measurements and viewing of the cross section as the technician adjusts final occlusion.

Figure 6A-D: Setup Review: Manual Setup – Photos from predefined views.

Figure 7: Setup Review: Digital Setup – 3D-Display.

Once the final occlusion is obtained, an optional setup review is available for the doctor. For wax and plaster, photographs are taken of the setup.

Much more is available to the doctor with the 3D digital setup, including use of some of the measurement and viewing tools that are available to the setup technician. According to data collected

from customer evaluation, the digital visualization also allows efficient communication and documentation of the intended treatment plan to the patient. In addition, orthodontists preferred viewing superimposed setup and malocclusion models in the 3D image display to photos of stone models (Figure 6A-D, Figure 7).

So how do we know that the digital setups are equal to or better than plaster model?

As part of the project, digital setups were printed and scored with the same quality checks used for many years to assess Incognito™ Appliance System physical models or setups (Figure 8A-B). They met or exceeded all historical standards for Incognito System setups.

Figure 8A-B: Occlusion checks during the validation process.

8A

8B

More critically, many hundreds of Incognito System cases made with digital setups have been placed in treatment with experienced users, and the Incognito System with Digital Setup has been preferred by the evaluators. Earlier this year, digital setups were rolled out to Global Incognito System users as part of the Incognito™ Lite Appliance System, launched in Spring 2012 for mild to moderate misalignment cases. Digital setups for full cases are becoming available now, with the rollout schedule depending on region of the world. Doctors can choose between a traditional wax and plaster setup or a digital setup for their Incognito Appliance System. All the advantages of the digital technology revolution are now available for users of the Incognito Appliance System.

References1. Grauer, Dan and Proffit, William R.. “Accuracy in tooth positioning with a fully

customized lingual orthodontic appliance.” AJO/DO, 2011 Volume 140, Number 3.

2. Thalheim A, Schwestka-Polly R., “Clinical realisation of a setup in lingual orthodontics.” Inf Orthod Kieferorthop, 2008; 40:277-82.

Reprinted from Orthodontic Perspectives Vol. XIX No. 2. © 2012, 3M. All rights reserved.