Preparation of low shrinkage stress dental composite with synthesized dimethacrylate oligomers

Two dimethacrylate oligomers named polypropylenglycol bis(2-hydroxy-3-methoxypropyl) dimethacrylates (380PPMA and 640PPMA) with different molecular weight were synthesized through ring opening addition reaction between epoxy terminated oligomers PPDE and methacrylic acid, and their structures were confirmed by FT-IR and ¹H-NMR spectra. The PPMAs were used to replace TEGDMA partially in Bis-GMA/TEGDMA (50/50, wt./wt.) with the aim to reducing volumetric shrinkage and shrinkage stress of dental resin composites. Dental resin composite without PPMAs was used as control. Double bond conversion (DC), volumetric shrinkage (VS), shrinkage stress, water sorption (WS) and solubility (SL), flexural strength (FS) and modulus (FM) of experimental dental resin composites were investigated. Dynamic mechanical analysis (DMA) was used to evaluate the glass transition temperature (Tg), heterogeneity, and crosslink density (υ). The results showed that dental resin composites contained 640PPMA had slower polymerization rate. Only dental resin composites with 20 wt% of 640PPMA in resin matrix had lower VS than control group (p < 0.05). All of PPMAs containing composites had lower shrinkage stress than control group (p < 0.05). Before water immersion, all of experimental dental resin composites had the same FS and FM (p > 0.05), while after water immersion, FM of dental resin composites with PPMAs became lower than control (p < 0.05). Higher WS and SL were observed in composites with 640PPMA (p < 0.05). Incorporation of PPMAs into dental resin composites could decrease Tg and crosslink density (p < 0.05), but more homogeneous materials could be obtained (p < 0.05). Therefore, PPMAs could be used to reduce volumetric shrinkage and shrinkage stress of dental resin composites, but further studies concerned biocompatibility and service life should be taken because of the higher WS and SL.