Posterior Resin Composites : Are the compressive properties of composites affected by water sorption? Vasiliki Maseli a DDS, Maria M. Karabela b, Konstantinos Kyritsis c, Dimitrios Tsivoulas d, Vasileios Prantsidis e Resident, Department of Cariology, Restorative Sciences and Endodontics, The University of Michigan, School of Dentistry, Ann Arbor, MI, USA b Laboratory of Organic Chemical Technology, Department of Chemistry, Aristotle University of Thessaloniki, Greece c DMP Ltd, Department of Research and Development, Kalyvion Avenue, Markopoulo 190 03, Greece d School of Materials, The University of Manchester, Grosvenor Street, M1 7HS, Manchester, UK e College of Engineering, Chemical Engineering Department, Swansea University, SA2 8PP, Wales,UK a PURPOSE In the oral environment, resin-based composites used in posterior restorations are subject to compressive stresses due to mastication. In addition, composites may absorb water and chemicals, such as those found in saliva or foods and may release components to their surrounding. Therefore, the oral conditions affect the stability and longevity of the restorations. The aim of this study is to determine the compressive properties and water sorption characteristics of dental light-curing resin based composites used in direct posterior restorations. The null hypothesis of this study is that a prolonged immersion of composites in aqueous environment will affect the compressive properties of the materials. MATERIALS AND METHODS Commercially available composites studied:  Filtek P60 (3M-ESPE)  Rok (SDI)  Surefill (Dentsply)  Tetric EvoCeram Bulk Fill (Ivoclar Vivadent)  x-tra fill (Voco)  Bright Posterior (DMP) Compressive strength was measured according to the ANSI/ADA No.27 specification, after storage of the composites in distilled water (37oC), for 24 hours and 30 days respectively. Water sorption characteristics were determined according to the method described in ISO 4049. The uptake of water was recorded for 30 days. RESULTS Compressive strength, water sorption and solubility of all studied materials ranked within the range of clinically accepted composites. Compressive strength Filtek P60, Surefill and Bright Posterior showed higher values of compressive strength after 24 hours of water storage. After 30days of immersing composites in water, a decrease in compressive strength was observed for Surefill and Rok. A reduction of compressive strength between 1 and 30 days was also reported Tetric EvoCeram Bulk Fill. On the contrary, Filtek P60, x-tra fil and Bright Posterior composites showed no significant change in compressive strength between 1 and 30 days of immersion. Figure 1. Compressive strength of posterior composites, after 24 hours and 30 days of water storage Composites with the highest solubility showed the highest difference in compressive strength between 1 and 30 days of immersion in water. Water Sorption Figure 3. Difference in compressive strength between 1 and 30 days of immersing composites in water versus solubility. Figure 2. Water sorption and solubility of posterior composites, after 30 days of immersion in water Bright Posterior, x-tra fill and Surefill sorbed the lowest amount of water. Xtra fill and Bright Posterior showed the lowest solubility values. On the contrary, Rok and Surefill exhibited the highest solubility values. A prolonged immersion of light cured resin-based composites in aqueous environment affects their compressive properties. Age-related changes in the compressive strength of resin-based composites, due to water storage, depends on the resin chemical structure and on the filler–resin bond strength. The aqueous oral environment affects the stability and longevity of the restoration. Therefore, composites with low water sorption and solubility values combined with high compressive strength will enhance the clinical performance of the restoration. FDI 2013 Istanbul Annual World Dental Congress 28 – 31 August