Effect of Preheating on the Mechanical Properties of Resin Composites Mine Betül Uctaslia Hacer Deniz Arisub Lippo VJ Lasillac Pekka K. Valittud AbstRAct Objectives: The purpose of this study was to compare the flexural strength and modulus of two commercial resin composites, at room temperature and 40, 45 and 50°C prior to light polymerization with standard and step-cure protocols. Methods: One nanohybrid (Grandio, VOCO, Cuxhaven, Germany), and microhybrid composite resin (Filtek Z250, 3M ESPE, St. Paul, MN, USA) were used. The materials were inserted into rectangular moulds at room temperature or preheated to a temperature of 40, 45 or 50°C and cured with standard or step-cure protocols with high intensity halogen (Elipar Highlight, 3M-ESPE, St. Paul, MN, USA). Ten specimens were prepared for each preheating and light curing protocol. A three-point bending test was performed using a universal testing machine at a crosshead speed of 1 mm/min. The data were analyzed by one-way analysis of variance and Tukey’s post hoc tests (P<.05) to examine the effect of curing protocol and preheating. Pearson’s correlation test was used to determine the correlation between tested mechanical properties and preheating. Results: There were no statistically significant difference between tested mechanical properties of the materials, curing protocols and temperature of the materials. No significant correlation was found between preheating and tested mechanical properties. Conclusions: The mechanical properties of the tested materials did not changed by preheating so the tested materials could be preheated because of the other potential clinical advantages like more adaptation to the cavity walls. (Eur J Dent 2008;2:263-268) Key words: Resin composite; Preheating; Polymerization. a Assistant Professor, University of Gazi, Faculty of Dentistry, Department of Operative Dentistry & Endodontics, Turkey. b Lecturer, University of Gazi, Faculty of Dentistry, Department of Operative Dentistry & Endodontics, Turkey. c Professor, University of Turku, Institude of Dentistry, Department of Prosthetic Dentistry & Biomaterial Science, Finland. October 2008 - Vol.2 d Professor, University of Turku, Institude of Dentistry, Department of Prosthetic Dentistry & Biomaterial Science, Finland. Corresponding author: Hacer Deniz Arisu University of Gazi, Faculty of Dentistry, Department of Operative Dentistry & Endodontics 8. Cadde 82. Sokak 06510 Emek-Ankara / Turkey. Tel: + 90 312 2034123 Fax: +90 312 2239226 E-mail: hdenz@yahoo.com, hacer@gazi.edu.tr 263 European Journal of Dentistry