d e n t a l m a t e r i a l s 2 9 ( 2 0 1 3 ) 1020–1025 Available online at www.sciencedirect.com jo ur nal ho me pag e: www.intl.elsevierhealth.com/journals/dema Mechanical behavior of a bi-layer glass ionomer Clarissa C. Bonifácio a,* , Niek de Jager b , Cornelis J. Kleverlaan b a Department of Conservative and Preventive Dentistry, Academic Centre for Dentistry Amsterdam, Amsterdam, The Netherlands b Department of Materials Science, Academic Centre for Dentistry Amsterdam, Amsterdam, The Netherlands a r t i c l e i n f o Article history: Received 29 October 2012 Received in revised form 21 May 2013 Accepted 3 July 2013 Keywords: Glass ionomer Flexural strength Young’s modulus Finite element analysis a b s t r a c t Objective. A high-viscosity consistency of the glass-ionomer cement (GIC) may lead to poor adaptation into the cavity. The use of a flowable GIC layer seemed to improve its adaptation in approximal restorations in vitro. In this study we assessed the flexural strength of a two-layered GIC, using a flowable GIC as a liner (two-layer technique). Additionally, finite element analysis on standardized bar-shaped models and on a representative tooth model was performed to rationalize the obtained results. Methods. The flexural strength and Young’s modulus were calculated from the results of a three-point-bending test. Bar-shaped specimens were prepared either with a conventional GIC, with a flowable GIC (powder/liquid ratio 1:2), or with two-layers (either with the flowable layer down or on the top of the specimen). Three dimensional FEA models of the bar-shaped specimens and a model of tooth 46 provided information on the stress distribution of each component of the specimen and on the restoration. Results. The apparent flexural strength and Young’s modulus of both two-layered groups were significantly lower than that of the conventional group. FEA showed that the layers of the two-layer specimens with the flowable GIC down separated from each other under load. The tooth model showed better stress distribution for the two-layer restorations. Significance. The two-layer GIC showed inferior flexural strength, which might be explained by the detachment of the layers under load. Nevertheless the tooth model showed that the two-layer GIC provides a lower stress concentration on the occlusal surface of the material. © 2013 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved. 1. Introduction Glass ionomer cements (GIC) are the most used filling mate- rial for minimal invasive restorations done by Atraumatic Restorative Treatment (ART) [1]. Essentially, this is due to the combination of its adhesive properties with a relatively slow chemical setting reaction, and a possible therapeutic effect on demineralized enamel and dentin provided by the fluoride ∗ Corresponding author at: Department of Conservative and Preventive Dentistry, Academic Centre for Dentistry Amsterdam (ACTA), Gustav Mahlerlaan, 3004, 1081LA Amsterdam, The Netherlands. Tel.: +31 205980597; fax: +31 205980597. E-mail address: C.Bonifacio@acta.nl (C.C. Bonifácio). released from the GIC [2]. Specially developed for ART, high- viscosity GICs have better mechanical properties than their predecessors [3–5], but because of their brittleness and diffi- cult handling, their performance on multi-surface cavities is far from optimal [6–8]. With regard to the adaptation of any restorative mate- rial in a posterior proximal cavity, the cervical margin is the weakest point. A high-viscosity material may lead to diffi- cult insertion and cervical gaps, both of which contribute to 0109-5641/$ – see front matter © 2013 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.dental.2013.07.008