The aim of this study was to investigate the effect of preheating on microshear bond strength (MSBS) of silorane and methacrylate-based composite resins to human dentin. The teeth were randomly divided into three main groups: (1) composite resins were heated upto 68 degrees C; (2) cooled to 4 degrees C; and (3) control [room temperature (RT)]. Each group was then randomly subdivided into four subgroups according to adhesive system used [Solobond M (Voco), All Bond SE (Bisco), Clearfil SE Bond (CSE) (Kuraray), Silorane adhesive system (SAS) (3M ESPE)]. Resin composite cylinders were formed (0.9mm diameterx0.7mm length) and MSBS of each specimen was tested. The preheated groups exhibited the highest MSBS (p<0.001) and the groups cooled to 4 degrees C exhibited the lowest MSBS (p<0.001). The CSE showed higher MSBS than the other adhesives (p<0.001). This study concludes that preheating of composite resins may be an alternative way to increase the MSBS of composites on dentin. SCANNING 38:63-69, 2016. (c) 2015 Wiley Periodicals, Inc.