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An in Vitro Wear Investigation of Dental Ceramic Porcelain Veneers

In this study, an in vitro wear behaviour of dental ceramic porcelain veneers was investigated. The ceramic veneers were fabricated on NiCrMo substrate through glazing method. Surface morphology of the veneers was characterized by scanning electron microscopy (SEM). The wear tests were conducted with the porcelain veneers at different loads under in vitro conditions through a pin-on-plate configuration against a human tooth counterbody. The worn surfaces of the porcelain veneers and human tooth counter material were examined by optical microscope. Porcelain veneer samples exhibit higher wear resistance and lower dynamic friction coefficient and wear rate do not change significantly at a given distance up to 100 N of applied load. Introduction Restorations such as hybrid resin composites suffer from a limited longevity, due to the fact that resin composites remain susceptible to discoloration, wear and marginal fractures, reducing thereby the aesthetic result in long term. In search for more durable aesthetics, porcelain veneers have been introduced in the last decade. Glazed porcelain veneers were proposed to be durable for anterior restorations with superior aesthetics [1-3]. In recent decades, significant research has been undertaken in the attempt to improve wear resistance of dental materials. The development of an efficient and effective in vitro wear test therefore has the potential to make a significant impact in dental materials research. In this study, the wear tests were conducted on dental ceramic veneer in vitro condition by using pin-on-plate configuration against human tooth counterbody. The main aim of this study was to compare the wear rates and coefficients of friction of the ceramic veneer. Experimental studies Dental porcelain veneer (Ceramco II) was used as crown material. Materials used for making dental porcelain were plaster, wax, revetment, abraders, varnish, insulator, and porcelain powders and metallic substrates. Ceramic raw materials of the tooth porcelains mainly consisted of clay, kaolin, quartz and feldspar, while commercial dental porcelains were coated on NiCrMo metallic substrate using a glazing process. The coatings were fired at 960 °C for 10 minutes in a vacuum atmosphere. After fabrication of the porcelain veneers, surface morphology of the ceramic porcelain samples was characterized by using SEM. The samples in the form of 5.5 mm in a diameter and 20 mm length were prepared for sliding wear tests. Wear tests were carried out by using a universal wear-friction tester (PLINT TE 88) (pin on plate). The counter material was prepared from human tooth. Tests were performed with normal load of 50, 100 and 150 N. The tests were performed at a sliding speed of 0.3 Hz with a stroke length of 8 mm. Samples were subjected to wear for 7200 s. After each test, wear rates and coefficients of friction of the ceramic veneer samples were determined. The worn surfaces of the human tooth counter material were examined by optical microscope. Key Engineering Materials Online: 2004-05-15 ISSN: 1662-9795, Vols. 264-268, pp 2005-2008 doi:10.4028/www.scientific.net/KEM.264-268.2005 © 2004 Trans Tech Publications Ltd, Switzerland All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications Ltd, www.scientific.net. (Semanticscholar.org-13/03/20,18:14:24) Results and Discussion Fig.1.shows the variation of friction coefficient of dental ceramic veneer in vitro condition with the applied load. The static friction coefficients are observed 0.286, 0.332 and 0.451 for applied loads of 50, 100 and 200 N, respectively. It is clear from this figure that increase the applied load leads to increase in static friction coefficient as expected. The samples exhibited lower dynamic friction coefficient than static friction coefficient at the loads of 50 and 100 N. In contrast, at the applied load of 200 N this behaviour was reversed and the dynamic friction coefficient was found close to static friction coefficient. These results point out that samples show better wear resistance up to 100 N load, beyond this load samples show a marked increase in wear rate (Fig. 2.). Fig. 1. The variation of friction coefficient as a function of applied load Fig. 2. The variation of wear rate as a function of applied load Wear rate of the samples for 50, 100 and 200 N loads as a function of time are presented in Fig.2. The trends established in this figure, firstly, wear rate of the samples at a given sliding distance up to 100 N exhibits little changes with time. In contrary, for the highest applied load, the wear rate increases steadily with increasing time. This behaviour may be explained by the fact that, 0 0,1 0,2 0,3 0,4 0,5 0,6