QMT Features: November 2011
Yes, we scan!
Can you scan it? Yes, we scan!  On show at Vision 2011 in Stuttgart last November was claimed to be  the the world’s smallest optical 3D dental scanner developed by the Austrian Institute of Technology

A high level of miniaturisation, especially in  the stereo vision camera and the projection optics, has made it possible to produce the smallest and lightest 3D dental scanner for intraoral applications. The system is simple and can be used on a standard PC without any previous technical knowledge.

The related software developed at the Austrian Institute of Technology,  (AIT) records all images in real time and transmits the data to the computer via a USB port. The captured data is used to generate a 3D image in real time. The 3D intraoral scanner is fury mobile and can be utilised everywhere. The result is available in a standard format and can be used by a normal CAD/CAM system in the dental industry.

Impression vs. digital measurement
To date, teeth have been cast using an impression compound in the mouth, a rather unpleasant and time-consuming process for the patient. The impression is then moulded with plaster and the resulting plaster model of the teeth prepared. Afterwards, the model is measured and digitised using a stationary scanner. In the final step, the dentures are produced with the aid of CAD/CAM.

Now,the 3D dental scanner  can show fully digital tooth images. Dental impressions using plastic impression compounds, an unpleasant process for patients, will therefore be rendered obsolete. A data file is created directly during the scan. Previously, this file could only be created via several intermediate steps (impression compound, plaster model, preparation of the plaster model).

To ensure that all images of a denture half can be perfectly joined with the correct positioning and orientation, clear reference points are essential in automatic extraction. In order to produce this on white teeth material,  AIT developed a special illumination system. The stereo method for measuring teeth and the exact design of the scanner have been successfully patented jointly by a-tron3d and the Austrian Institute of Technology, (a.tron3d holds the exclusive rights for the dental industry)

AIT is the largest non-university research facility in Austria. With its five departments, the AIT regards itself as a highly specialised research and development partner for industry. The researchers examine key infrastructure areas of the future: health & environment, safety & security, energy, mobility, and foresight & policy development. Around 1,100 employees carry out research all over Austria - primarily at the main locations of Vienna, Seibersdorf, Vienna Neustadt, Ranshofen and Leoben.

In 2003 and 2004, the first research and development work was carried out on stereo vision technology, which was used in 2005 in the form of the first stereo vision sensor during the Darpa Grande Challenge, the US desert rally for autonomous vehicles.  Subsequently, the technology has been developed for the dental industry jointly with an  industry partner, a.tron3d,  and  in 2011 the prototype of the world’s smallest optical 3D scanner was officially presented at the Dental Show in Cologne.

The stereo dental scanner is about ten times smaller and considerably less expensive to manufacture than other systems currently on the market. The minitiarisation  of the components used in the dental scanner presented developers with a special challenge. Christoph Nowak, specialist at AIT for safe and autonomous systems, recalls, “Much of what  was required  in these dimensions represented  pioneering work. In order to capture a 3-dimensional image, two cameras at a clearly defined  distance are required. This distance is very small with an oral scanner. In addition, due to the minimal distance from the object to be scanned, special wide-angle lenses needed to be employed.  Distortions caused by the lens are automatically corrected by the AIT software. Due to the small lens distance, the scanner achieves the most precise results close to the  object.” The compact scanner can capture about two molars at once and is simply moved along an arc from front to back over the teeth.

With thousands of of measuring points generated during one scan, the data is processed continuously by the S3E - High Speed stereo Software Engine - a software system developed by the Embedded 3D Vision research team, which combines the best images to render a 3-D model. Factors such as distance, surface structure and exposure time play a role in this process.

A critical task in this process is to automatically extract unique reference points to seamlessly merge  all images belonging to either half of a set  of teeth, in the correct position and properly aligned. With white teeth, this is only feasible using a special illumination  system developed by AIT. Specifically, a random pattern  consisting of light defined wavelengths is projected onto the surface. There is thus no need for any aids, such as special powders, to enhance contrast.

A patent has been registered for the stereoscopic technique for scanning teeth, including the required mirror system for projecting the light pattern to every point. Nowak explains, “Measuring point quality is evaluated in real time with considerable volumes of data generated in the process.” The scanned image of the upper and lower jaws is ultimately reduced to approximately 30MB. The current processing speeds of up to 6 measurement datasets per second deliver a complete jaw arch measurement in 3 to 5 minutes. The measurement accuracy is approx. 20 µm for an individual measurement. l


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