Thermal and spectral behaviour of a light-cured methacrylate-based composite material used in dentistry
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Thermal and spectral behaviour of a light-cured methacrylate-based composite material used in dentistry H. O. Manolea • P. Rotaru • G. Manolea E. Morıˆntale • R. Rıˆca˘
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Received: 1 January 2013 / Accepted: 2 April 2013 Ó Akade´miai Kiado´, Budapest, Hungary 2013
Abstract The evolution of the polymerization of a light-cured methacrylate-based composite material (Pekalite) used in dentistry was studied. Fourier transform infrared spectroscopy and thermal analysis (TA) showed that with increasing the photo-polymerization time from 5 to 60 s, the degree of conversion increases from 32.5 to 59.6 % and thermal stability of the composite material increases from 144.6 to 270 °C. Growth of photo-polymerization time from 5 to 60 s produces an improvement in the mechanical strength of the composite material from 153 to 248 MPa. Spectral analysis and TA are two complementary and rapid methods for determining the degree of polymerization of composite materials used in dentistry. Keywords Light-cured material used in dentistry Methyl methacrylate Thermal analysis Fourier transform infrared spectroscopy Degree of conversion
H. O. Manolea R. Rıˆca˘ Department of Dental Materials, Faculty of Dentistry, University of Medicine and Pharmacy Craiova, 2-4 Petru Rares¸ Street, 200349 Craiova, Romania P. Rotaru (&) E. Morıˆntale Department of Physics, Faculty of Exact Sciences, University of Craiova, 13 AI Cuza Street, 200585 Craiova, Romania e-mail: [email protected]; [email protected] G. Manolea Department of Electromechanics, Faculty of Electrical Engineering, University of Craiova, 107 Decebal Boulevard, 200440 Craiova, Romania
Introduction The light-cured resins are materials widely used in the dental office. A resin composite material is formed of four major components: organic polymer matrix, inorganic filler particles, coupling agent, and the initiator–accelerator system. The polymerization of light-cured composites is initiated by visible blue light [1]. In the photo-polymerization of composite resins, light intensity is a critically importance factor, as it is directly related to the number of photons delivered. Because the properties of these resins after curing are affected by the degree of polymerization, it is important to study the polymerization deeper [2]. Most of the visible light-cured resins contain a photo-sensitiser such as camphorquinone, and a reducing agent-like tertiary amine [3] that causes the initiation of polymerization via visible light irradiation. Through the activation of the photo-initiator, formation of free radicals, splitting of C=C double bonds to C–C single bonds by free radicals, and formation of polymer chains are achieved [4]. In the transformation from monomer structures to polymer chains, the larger van der Waals intermolecular spacing is replaced by the smaller intramolecular covalent bonds [5]. The degree of conversion (DC) is an important parameter influencing the final physical and biological properties of composites. Lower conversion values may also result in a
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