To compare two kind of resin-based dental composites, the polymerization shrinkage, contraction stress (CS), and degree of conversion (DC) of four dimethacrylate-based and one silorane-based composite were investigated. To determine shrinkage, the composites were packed, respectively, into a cylindrical cavity in human teeth and imaged using X-ray microcomputed tomography to determine the precise volume before and 30 min after photopolymerization. To determine CS, the sample was applied in a similarly sized cylinder in a universal testing machine and monitored for 30 min. FTIR spectroscopy was used to determine DC. The volumetric shrinkage (range: 1.1-3.1%) and maximum CS (range: 1.2-3.5 MPa) differed significantly among the tested composites but not the final DC (range: 62.3-69.1%). The silorane-based composite displayed the lowest volumetric shrinkage and CS of all composites. No correlation was observed between the stress and volumetric shrinkage values of the dimethacrylate-based composites. A moderate correlation was found between stress and DC (r = 0.836), which was significant at 20 and 40 s. The silorane-based composite exhibited superior shrinkage behavior compared with conventional dimethacrylate composites with comparable polymerization kinetics. The CS was dependent on multiple variables, including the volumetric shrinkage, DC, and curing rate. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 1882-1888, 2011