Dental restorative composites containing spiro orthocarbonates (SOCs) have been studied extensively to minimize the volumetric shrinkage that occurs during polymerization. Previous reports suggested that dental composites with low volumetric shrinkage could be obtained by mixing SOC with conventional resins. However, its inclusion had adverse effects on the mechanical properties of dental composites. A novel SOC (2,2-bis-4,4'-(7-phenyl-1,4,6,9-tetraoxaspiro[4.4]nona-2-ylmethoxyphenyl )propane), SOC-N, was synthesized to overcome these adverse effects resulting from the previously developed SOCs. The mechanical strength and volumetric shrinkage of the dental composites composed of 70 wt% inorganic fillers and resin matrices containing SOC-N, 2,2-bis-[4-(2-hydroxy-3-methacryloyloxy propoxy) phenyl] propane (Bis-GMA), and triethylene glycol dimethacrylate (TEGDMA) were explored. When compared to a control resin-containing composite (Bis-GMA/TEGDMA=70/30), the volumetric shrinkage of the composite containing new resin matrix, obtained through the addition of SOC-N to the Bis-GMA/TEGDMA=70/30 mixture, was reduced gradually by increasing the SOC-N content. Furthermore, the latter sample showed better mechanical strength than the former when the resin matrix contained 30 wt% SOC-N.