Int Poster J Dent Oral Med 2003, Vol 5 No 01, Poster 163
Evaluation of dental restorations with occlusal surfaces - A new approach -
Authors: ZÄ Heike Rudolph1, Dr.-Ing. Christine Schöne2, Dr. Anke Weber1, ZÄ Silke Benzinger1, ZA Sebastian Quaas1, Henning Sporbeck1, OA Dr. Ralph Luthardt1
1Department of Prosthodontics, Medical Faculty, Dresden University of Technolgoy
2Institute for Production Automatisation and Control Technologies, Dresden University of Technology
3. wissenschaftliche Tagung des Arbeitskreises für Angewandte Informatik in der Zahn-, Mund- und Kieferheilkunde
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Introduction/Aim of the study
Mainly, the occlusal fit of prosthodontic restorations is evaluated qualitatively by visual control of color-marked contact points. A large loss of data and information is immanent in conventional methods for the exploration of internal, marginal and occlusal fit of fixed restorations.
Aim of this study was to develop a procedure for the three-dimensional analysis of internal and occlusal precision of fit.
Material and Method
A test model was developed by reverse engineering. Every single step in the manufacturing of fixed prosthodontic restorations concerning the influence on the achievable precision has to be evaluated. The test model is based on a real and an identical virtual model of upper and lower teeth in static occlusion.
Starting point were full arch master-casts of the upper and lower jaw (teeth 14, 16 and 36 prepared with a chamfer, tooth 15 missing). The master-casts were optically digitized with a measuring error of ± 10 µm (ODKM, IVB GmbH, Jena, Germany; Fraunhofer Institut für angewandte Optik und Feinmechanik, Jena, Germany).
|Fig. 1: Starting point of the reverse-engineering process.
To avoid undercuts, point clouds were reduced manually, then filtered and exported in ASCII-format (Argus, IOF, Jena, Germany). With Surfacer® (Version 10.6, Imageware Inc., Ann Arbor, Michigan, USA) points differing more than 10 µm from a plane respectively a sphere were removed from the data sets.
Based on the point clouds, surfaces as smooth as possible were created with Surfacer® for each tooth (curve mesh with 240 control points). With maximum smoothness, influences of roughness or surface structure on the results within the single steps of manufacturing were avoided.
|Fig. 2: Virtual Model optimized for CAD/CAM purpose.
Minimizing the deviation between virtual model and real model, areas which caused difficulties in fabrication were specifically modified.
The processing error had to be determined. For this reason, impressions were taken of the real model's metal teeth (Dimension Penta H, Dimension Garant L, Pentamix-machine, 3M Espe AG, Germany) and master cast dies were made (esthetic rock 285, dentona, Germany). The dies were digitized again. The error of impression-taking and die-making averaged 8 µm. Data sets were aligned to the reference surfaces of the virtual model. Surface-Cloud-Differences between point cloud and respective surface of each tooth were analyzed qualitatively and quantitatively.