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DIGIDENT - A DIGITAL PHOTOGRAMMETRIC TOOL FOR DENTISTS 
by Wolfram Hóflinger ! and Gerhard Brandstätter 2 
! P.O B. 441 
A-6021 Innsbruck 
Tel. ++43 512 581316 
Fax. ++43 512 577994 
? Graz University of Technology 
Steyrergasse 30 
A-8010 Graz 
KEYWORDS: biometrics, deformation analysis, geometric constrained template matching, non targeted objects 
ABSTRACT: 
DigiDent is a CCD-camera based tool for dentists. Its purpose is the measurement of the three-dimensional position and 
orientation of every single tooth with an accuracy better than 100 microns. Especially the change of orientation and position during 
an orthodontic treatment shall be detected. From that point of view DigiDent can be classified as a tool for 3D deformation 
measurement in a very close range, the mouth. The following paper will deal with algorithmic and conceptual aspects. Systems 
calibration and surface reconstruction will be addressed in detail. 
1. THE PURPOSE OF DIGIDENT 
The use of photogrammetry in medicine is not a new idea (Voizikis, 1985), even in dentistry (Mollersten 1989) and (Achilli 1992). 
Now it shall be applied to monitor three-dimensional position and orientation changes of teeth during an orthodontic treatment. 
Dentists try to move and turn a single tooth or groups of teeth. Distal, mesial and especially torkquing movements have to be 
monitored, so that the teeth will move and rotate to the wished positions and orientations. To monitor the results of the treatment 
spatial position and orientation of every single tooth have to be measured periodically. 
At the moment, position and orientation changes of the teeth are measured manually using an electronic caliper. On the outer side 
of the teeth brackets are bonded. They hold wires or other fixed appliances. Their design is strongly influenced by the measured 
movements of the teeth, to make them move to the correct position. Little cubes of approximately 4 mm sidelengths are screwed to 
the brackets. Since all measurements are done directly in the mouth, only little space is left to apply the electronic caliper. 
Distances are measured between the cubes. Since the electronic caliper is not very small, doing the measurements is not a great 
pleasure for the patient. On the other hand calculated positions and orientations of the teeth are not very accurate and reliable since 
only few distances can be measured in the mouth and cutting angles are very small. So there are two main reasons why dentists are 
looking for a better measurement method: firstly they want a better, more reliable and more powerful system, secondly making the 
measurements shall get more comfortable for the patients. 
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Fig.1: Modell of upper jaw with bonded brackets and fixed cubes. Fig.2: Measuring a distance with the electronic caliper 
2. HARDWARE AND CONCEPTUAL ASPECTS 
Since DigiDent shall become a commercial product standard components are used. Two PULNiX TM765 E 2/5" CCD cameras and 
16 mm Cosmicar / Pentax lenses are used. Images are grabbed with two standard video boards that are installed in a HP PC based 
station. For some field tests imagery was recorded on a Blaupunkt VHS recorder. To make image acquisition possible a special 
IAPRS, Vol. 30, Part 5W1, ISPRS Intercommission Workshop "From Pixels to Sequences”, Zurich, March 22-24 1995