Degradation processes in dental ceramic composites
Joanna Siejka-Kulczyk*, Małgorzata Lewandowska*, Gabriel Rokicki**, Mikołaj Szafran**, Krzysztof J. Kurzydłowski*** *Warsaw University of Technology, Faculty of Materials Science and Engineering, Wołoska 141, 02-507 Warsaw, Poland **Warsaw University of Technology, Faculty of Chemistry, Koszykowa 75, 00-671 Warsaw, Poland ***Warsaw University of Technology, Faculty of Materials Science and Engineering, Wołoska 141, 02-507 Warsaw, Poland
Quarterly No. 2, 2006 pages 50-54
DOI:
keywords: dental materials, ceramic - polymer composites, degradation, polymerization shrinkage
abstract The paper describes the degradation processes that proceed in dental ceramic/polymer composites as a result of the action of environment, polymerization shrinkage and tribological wear. The results are analyzed in terms of the perspectives for application of these composites. In the present study the composites based on the bis-GMA resin reinforced with (i) a ceramic glass microfiller (average particle size of 5 μm) and (ii) ceramic glass microfiller combined with nanosilica (average particle size of 40 nm) were investigated. Samples of composites in the form of 2 x 2 x 25 were exposed to solutions with varied pH, including 0.1M NaOH (pH = 13), 0.1M CH3COOH (pH = 3) and distilled water (pH = 7) in order to compare the stability of their properties. The microstructure (Figs. 1, 2) and the mechanical parameters (such a flexural strength and microhardness) (Fig. 3) of the materials before and after the exposure were examined for the exposure time of 15 h. In order to reduce polymerization shrinkage, two approaches were considered: (a) a modification of bis-GMA resin and (b) the use of a nanofiller. The results have shown that addition of hyperbranched macromonomer of metacrylane to bis-GMA resin decreases the shrinkage by 30% (Fig. 4). The polymerization shrinkage can further be reduced by adding ceramic microfiller and nanofiller (Figs. 5, 6). One of the parameters, which can be used to characterize the tribological properties of the materials, is the coefficient of friction μ . The influence of nanosilica content on the coefficient μ is shown in Figure 7 for different testing loads.