Journal of Biomaterials Science 20 (2009) 1831–1844 www.brill.nl/jbs Physical Properties of a Hybrid and a Nanohybrid Dental Light-Cured Resin Composite Irini D. Sideridou a,∗ , Maria M. Karabela a , Christina N. Micheliou a , Panagiotis G. Karagiannidis b and Stergios Logothetidis b a Laboratory of Organic Chemical Technology, Department of Chemistry, Aristotle University of Thessaloniki, GR-5412 Thessaloniki, Greece b Lab of Thin Films-Nanosystems and Nanometrology, Department of Physics, Aristotle University of Thessaloniki, GR-54124 Thessaloniki, Greece Received 22 July 2008; accepted 22 October 2008 Abstract This work was aimed at the study of some physical properties of two current light-cured dental resin com- posites, Rok (hybrid) and Ice (nanohydrid). As filler they both contain strontium aluminosilicate particles, however, with different size distribution, 40 nm–2.5 μm for Rok and 10 nm–1 μm for Ice. The resin matrix of Rok consists of UDMA, that of Ice of UDMA, Bis-EMA and TEGDMA. Degree of conversion was de- termined by FT-IR analysis. The flexural strength and modulus were measured using a three-point bending set-up according to the ISO-4049 specification. Sorption, solubility and volumetric change were measured after storage of composites in water or ethanol/water (75 vol%) for 1 day, 7 or 30 days. Thermogravimetric analysis was performed in air and nitrogen atmosphere from 30 to 700 ◦ C. Surface roughness and morphol- ogy of the composites was studied by atomic force microscopy (AFM). The degree of conversion was found to be 56.9% for Rok and 61.0% for Ice. The flexural strength of Rok does not significantly differ from that of Ice, while the flexural modulus of Rok is higher than that of Ice. The flexural strengths of Rok and Ice did not show any significant change after immersion in water or ethanol solution for 30 days. The flexural modulus of Rok and Ice did not show any significant change either after immersion in water for 30 days, while it decreased significantly, even after 1 day immersion, in ethanol solution. Ice sorbed a higher amount of water and ethanol solution than Rok and showed a higher volume increase. Thermogravimetric analysis showed that Rok contains about 80 wt% inorganic filler and Ice about 75 wt%.  Koninklijke Brill NV, Leiden, 2009 Keywords Dental composites, degree of conversion, flexural properties, thermogravimetric analysis, sorption solubil- ity, volumetric change, surface morphology, AFM * To whom correspondence should be addressed. Fax: (30-210) 2310-997769; e-mail: siderid@chem.auth.gr  Koninklijke Brill NV, Leiden, 2009 DOI:10.1163/156856208X386435