MSc (Dentistry), Faculty of Health Sciences, University of the Witwatersrand, 2009 / Problem. One of the sources of inaccuracy in utilising the CEREC Chairside CAD/CAM system has been the difficulty of accurately positioning the intraoral camera relative to the path of insertion of the preparation and restoration. The degree of inaccuracy produced by variations in the angulation of the camera relative to the path of insertion is not known.
Purpose. The purpose of this study was to first review the literature and history of CAD/CAM in dentistry, and the CEREC Chairside System in particular, and then to determine the errors that may result from changes in angulation of the camera in three dimensions. Further, to design a device which would help stabilise the camera to eliminate such errors.
Method and Materials. A prefabricated Aesthetic Base Gold (ABG) Model was used and mounted on an articulator in order to simulate changes in angulation of each of the three dimensional axes which cause variations in roll, pitch, and yaw in the positioning of the camera. Images were captured for angle variations of 0°, 1°; 3°, 5°, 10°, 15° and 20° using the CEREC software on a crown preparation for tooth 24. The same software was used to make measurements on the resulting images to determine the mesio-distal, bucco-lingual orientation and the occlusal, internal shoulder and external shoulder dimensions. In addition, a quality assessment was carried out to observe any shadows, surface texture changes, margin discrepancies and ability to automatically complete the restoration with ease and accuracy. An intraoral stabilising device was designed that could be placed intraorally using polyvinyl siloxane putty. The ABG model was positioned to simulate quadrants 2 and 4 on crown
iv
preparation for tooth 24. Time to set up and place the device was recorded, and a Visual Analogue Scale was used to determine ease of use. Results. Difficulties were encountered in measurements of images where there was an angle deviation of greater than 5º, and so it was only possible to analyse the four angles of 0, 1, 3, and 5º. A three-way ANOVA revealed expected significant differences between the different measurements (as they are measuring different things) but there were no other significant differences. Thus neither the four different angles nor the three different axes had any influence on the readings. There was also consistency across the measurements, for every combination of the levels of the three factors (angle, measurement and axis). The stabilising device proved quick and easy to set up and place the silicone putty (less than 20 seconds) and the average VAS score for using the device improved by 25.3% when using the device in the lower, and by 36.4% when using the device in the upper arch. Conclusions. The angle of the camera relative to the path of insertion of the restoration should not exceed 3° for changes in Pitch, or 5° for changes in Roll and Yaw of the camera. The stability device designed during this study proved to be more convenient and accurate for data capture as it decreased the time of search and reduced both the internal and external factors which interfere with data capture.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/7954 |
| Date | 09 April 2010 |
| Creators | Muianga, Mick Ivan de Sousa |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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