Effects of barriers on chemical and biological properties of two dual resin cements Nocca G, Iori A, Rossini C, Martorana GE, Ciasca G, Arcovito A, Cordaro M, Lupi A, Marigo L. Effects of barriers on chemical and biological properties of two dual resin cements. Eur J Oral Sci 2015; 00: 000–000. © 2015 Eur J Oral Sci The aim of this study was to investigate the degree of conversion, monomer release, and cytotoxicity of two dual-cure resin cements (Cement-One and SmartCem2), light-cured across two indirect restorative materials in an attempt to simulate in vitro the clinical conditions. The results obtained show that the degree of conversion was influenced by both barriers, but the effect of the composite material was greater than that of the ceramic one. The amount of monomers released from the polymer- ized materials in the absence of barriers was significantly lower than that released in the presence of either the ceramic or the composite barrier. However, a higher amount of monomers was released in the presence of the ceramic barrier. All materials, in all the experimental conditions employed, induced slight cytotoxicity (5–10%) on human pulp cells. Our examinations showed that the two resin cements had similar chemical and biological properties. The decreased degree of conversion of the dual-curing self-adhesive composite showed that the light-curing component of these materials has an important role in the polymerization process. In clinical practice, it is therefore important to pay attention to the thickness of the material used for the reconstruction. Giuseppina Nocca 1,2 , Andrea Iori 3 , Carlo Rossini 3 , Giuseppe E. Martorana 1 , Gabriele Ciasca 4 , Alessandro Arcovito 1 , Massimo Cordaro 3 , Alessandro Lupi 2 , Luca Marigo 3 1 Facolt a di Medicina e Chirurgia, Istituto di Biochimica e Biochimica Clinica, Universit a Cattolica del Sacro Cuore, Rome; 2 Istituto di Chimica del Riconoscimento Molecolare, C.N.R., Rome; 3 Facolt a di Medicina e Chirurgia, Istituto di Clinica Odontoiatrica, Universit a Cattolica del Sacro Cuore, Rome; 4 Facolt a di Medicina e Chirurgia, Istituto di Fisica, Universit a Cattolica del Sacro Cuore, Rome, Italy Giuseppina Nocca, Istituto di Biochimica e Biochimica Clinica, Facolt a di Medicina e Chirurgia, Universit a Cattolica del Sacro Cuore, Largo Francesco Vito 1, 00168 Rome, Italy E-mail: g.nocca@rm.unicatt.it Key words: conversion degree; cytotoxicity; monomers leachability Accepted for publication January 2015 Indirect restorations are commonly used in dental prac- tice because of their esthetic properties, less time-depen- dent degradation and polymerization shrinkage, and time-saving chairside features (1). However, the applica- tion of an indirect restoration manufactured in the den- tal laboratory still requires direct cementation in the oral cavity. Resin-based luting agents are routinely used for the cementation of indirect restorations or in other clini- cal applications that require cementation in the oral cav- ity, and these materials must undergo polymerization via chemical curing, light-curing, or dual-curing (2, 3). Dual-cure materials are formulated to polymerize also in the absence of a visible light source, but, in this case, their degree of conversion (DC) is altered with respect to the manufacturer’s declared information. Indeed, the aim of dual-cure luting cements is to provide an ade- quate DC beneath restorations where the opacity of the material may hinder the transmission of sufficient light energy to the cement (4, 5). In fact, the energy for the light-curing process decreases during passage through materials because of the ‘light scattering phenomenon’ (5). In such conditions, polymerization of the portion of luting cement that receives insufficient light for the light- curing process to take place still occurs, via a catalyst that favors the auto-polymerization process (3, 6). This capability is very important in order for an adequate DC to be reached from which the mechanical and biological properties of the materials derive. A decrease of the DC could negatively influence the hardness of the resin layer by enhancing the leaching of monomers, with possible toxic effects on pulp cells. The amounts of bioactive molecules released and the degree of cytotoxicity are key parameters in the final evaluation of a biomaterial. In fact, many different harmful compo- nents can be leached from composite resins, in particu- lar, uncured dimethacrylic monomers or oligomers that may cause, or at least contribute to, adverse biological effects (7), such as damage to the oral soft tissues, which has already been observed in vivo (8), and a remarkable in vitro cytotoxicity in primary and immortalized cul- tures (9, 10). Research on biocompatibility of dental materials revealed that different methacrylates were able to induce glutathione depletion (11) and mitochondrial damage with a consequent increase of reactive oxygen species (ROS) production (12, 13). The DC is evaluated most commonly by Fourier transform infrared spectroscopy (FTIR), an analytical technique capable of determining the signal of the unreacted aliphatic C = C double bonds present in a polymerized sample (14). Since mid-2000s, dual-cure cements with improved handling properties have become commercially available. Eur J Oral Sci 2015; 1–7 DOI: 10.1111/eos.12178 Printed in Singapore. All rights reserved Ó 2015 Eur J Oral Sci European Journal of Oral Sciences