Uctasli, Arisu, Lasilla, Valittu No significant correlations were found between the flexural strength and preheating and also between the flexural modulus and preheating of the tested materials. When microhybrid resin composite (Z250) was cured with standard curing protocols, the flexural modulus was significantly higher when the resin composite material was preheated to a temperature of 40°C. However there were no significant differences in the other curing protocols. Also there were no significant differences between the curing protocols and between the temperatures for nanohybrid resin composite. The present study assessed the limited mechanical effects of preheating resin composites. Further research is needed for evaluating the effects of preheating on the other mechanical properties and on pulp tissue. ocnLusIons The results of this study showed preheating and different curing protocols did not have any harmful effect on the mechanical properties of the tested materials. So it could be concluded that these materials could be preheated because of the other potential clinical advantages like more adaptation to the cavity walls. RefRencs 1. Manhart J, Kunzelmann KH, Chen HY, Hickel R. Mechanical properties and wear behavior of light cured packable composite resins. Dent Mater 2000;16:33-40. 2. Poss SD. Using a new condensable composite for posterior restorations. Compend Contin Educ Dent Suppl 1999;23:14– 18. 3. Al-Sharaa KA, Watts DC. Stickiness prior to some light cured resin composites. Dent Mater 2003;19:182-187. 4. Blalock JS, Holmes RG, Rueggeberg FA. Effect of temperature on unpolymerized composite resin film thickness. J Prosthet Dent 2006;96:424-432. 5. Rodrigues Junior SA, Zanchi CH, Carvalho RV, Demarco FF. Flexural strength and modulus of elasticity of different types of resin based composites. Braz Oral Res 2007;21:16- 21. 6. Crim G, Chapman KW. Reducing microleakage in Class II restorations: an in vitro study. Quintessence Int 1994;25:781- 785. October 2008 - Vol.2 7. Schuckar M, Geurtsen W. Proximo-cervical adaptation of Class II composite restorations after thermocycling: a quantitative and qualitative study. J Oral Rehabil 1997;24:766-775. 8. Freedman PD. Clinical benefits of pre-warmed composites. Private Dent 2003;8:111-114. 9. FriedmanJ.Thermallyassistedpolymerizationofcomposite resins. Contemp Esthetics Rest Practice 2003;7:46. 10. Roeters JJ, Shortall AC, Opdam NJ. Can a single composite resin serve all purposes? Br Dent J 2005;199:73-79. 11. Powers JM, Wataha JC. Dental materials: properties and manipulation. St. Louis: Elsevier, 2003;68-72. 12. Hervas-Garcia A, Martinez-Lozano Ma, Cabanes-Vila J, Barjau-Escribano A, Fos-Galve P. Composite resins: a review of the materials and clinical indications. Med Oral Patol Oral Cir Bucal 2006;11:E215- 220. 13. Bagis YH, Rueggeberg FA. Effect of post cure temperature and heat duration on monomer conversion of photo- activated dental resin composite. Dent Mater 1997;13:228- 232. 14. Park SH, Lee CS. The difference in degree of conversion between light-cured and additional heat-cured composites. Oper Dent 1996;21:213-217. 15. Trujillo M, Newman SM, Stransbury J. Use of near-IR to monitor the influence of external heating on dental composite photopolymerization. Dent Mater 2004;20:766- 777. 16. Daronch M, Rueggeberg FA, De Goes MF. Monomer conversion of pre-heated composite. J Dent Res 2005;84:663- 667. 17. Daronch M, Rueggeberg FA, De Goes MF, Giudici R. Polymerization kinetics of pre-heated composite. J Dent Res 2006;85:38-43. 18. Roulet JF. The problems associated with substituting composite resins for amalgam: a status report on posterior composites. J Dent 1988;16:101–113. 19. Craig RG. Restorative dental materials. St. Louis: Mosby Publishing Co, 1997. 20. Lovell LG, Lu H, Elliott JE, Bowman CN. Understanding the kinetics and network formation of dimethacrilate dental resins. Polym Adv Technol 2001;12:335-345. 21. Muñoz CA, Bond PR, Sy-Muñoz J, Tan D, Peterson J. Effect of pre-heating on depth of cure and surface hardness of light-polymerized resin composites. Am J Dent 2008;21:215- 222. 22. Lovell LG, Lu H, Elliot JE, Stansbury JW, Bowman CN. The effect of cure rate on the mechanical properties of dental resins. Dent Mater 2001;17:504-511. 267 European Journal of Dentistry