Impedance as a measure of setting reaction in glass ionomer cements A. Moguš-Milanković a, ⁎, K. Sklepić a , M. Čalogović a , M. Marciuš b , K. Prskalo c , B. Janković c , Z. Tarle c a NMR Center, Ruđer Bošković Institute, Bijenička c. 54, Zagreb, Croatia b Division of Materials Chemistry, Ruđer Bošković Institute, Bijenička c. 54, Zagreb, Croatia c Department of Endodontic and Restorative Dentistry, School of Dental Medicine, University of Zagreb, Zagreb, Croatia abstract article info Article history: Received 19 December 2013 Received in revised form 20 February 2014 Available online xxxx Keywords: Dental cements; Impedance spectroscopy; Electrical conductivity; Capacitance The setting process for dental glass ionomer cements (GICs) was studied by impedance spectroscopy in a fixed, 10 and 1000 Hz, and wide frequency region, from 0.01 Hz to 1 MHz. For comparison, the setting of the conven- tional GICs, Fuji IX Fast and Ketac Molar Aplicap, and “resin modified” GIC, Fuji II LC, was investigated. The effect of setting upon electrical conductivity shows a significant decrease and break in conductivity for conventional GICs after the first 15 and 30 min, respectively. For light-activated Fuji II LC, only a drop without any evidence of a break in electrical conductivity was observed. Such behavior is the result of the instantaneous photopolymerization and formation of a rather homogeneous cement matrix. The complex impedance plots ob- tained for the three GICs studied show the presence of features that are attributed to the structural regions in the samples. Evolution of the impedance spectra and changes in the capacitance values reveal gradual transforma- tions related to the development of various constituent regions during the setting process. Thus, impedance spectroscopy could become an essential technique for the separation of the overall electrical properties into their component parts, which could then serve as the foundation for meaningful clinical impedance measure- ments in vitro and in vivo. The knowledge of the sequences of the setting reactions in dental cements is impor- tant as these will affect the handling and the overall physical properties of the cements. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Glass ionomer cements (GICs) were first described for use in dentist- ry in the early 1970s [1]. They have desirable properties, such as adhesion to moist tooth structure, remineralization effects and anticariogenic ac- tion due to fluoride release. However, GICs suffer from the disadvantage of being brittle. GICs consist of an aluminofluorosilicate glass powder and an aque- ous polyacrylic acid. Cement formation arises from the acid–base reac- tion between the components, glass powder and acid [2,3]. The surface of the glass is attacked by the acid, resulting in the leaching of available cations (e.g., Al 3+ , Ca 2+ ). Subsequently, the released cations are chelat- ed by the carboxyl groups and serve to cross-link the polycarboxylate chains ionically within the cement matrix. The numbers and types of cations and anions released from the glass determine the extent of the ionic cross-linking of the polysalt matrix and the properties of the ce- ments [4,5]. In addition, a light-cured GIC has also been investigated, where a resin and light-curing catalyst are added to hasten setting and improve esthetic performance. The diffusion of cations controls the cross-linking of the polymer matrix and enhances the strength, stiffness and insolubility of the cements. Hence, the properties and performance are strongly influenced by the setting and hardening processes. Al- though a considerable number of papers are available about the effect of glass composition on the GIC setting processes, there is little informa- tion on the electrical properties of dental cements. Impedance spectroscopy (IS), as a nondestructive method for deter- mining changes in a setting mechanism, has been used to study various types of materials, such as Portland cements, mortars and metallic den- tal materials [6–9]. Previous investigations of the microstructural devel- opments in cement-based materials reported that the analysis of the impedance spectra provides pore structure information [10,11]. It was found that there is a correlation between the pore size in cement paste and the impedance spectra. It was also demonstrated that the pre-drying history of cement paste prior to saturation with solution results in an increase in the total deformation partly due to the pore coarsening effect [12]. Few earlier studies have been focused on the dielectric properties of dental cements using impedance measure- ments [13–16]. A study of the multi-frequency electrical behavior of glass-polyalkenoate/resin cements reported that ionic conductivity and polarization are the dominant factors in fully solidified cements [17]. Furthermore, it was shown that the electrical measurements are sensitive to the kinetics of the setting reaction and correspond to the time-scale changes in impedance [17]. Journal of Non-Crystalline Solids 389 (2014) 93–103 ⁎ Corresponding author. Tel.: +385 1 4561 149; fax: +385 1 4680 114. E-mail address: mogus@irb.hr (A. Moguš-Milanković). http://dx.doi.org/10.1016/j.jnoncrysol.2014.02.012 0022-3093/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/ locate/ jnoncrysol