Shrinkage Stress of Composite Resin during Hardening

Part III The Effects of Amount of Polymerization Initiator on the Shrinkage Stress

Abstract

Three kinds of experiments were performed about the composite resin produced by way of trial which was mixed 60% irregular silica and the microfiller (MF) in the dimethacrylate contained the initiator varying 0.25 to 1.0%.
First, the linear shrinkage was measured with the apparatus which has a ditch equipped with the aluminium blocks at the each end. The linear shrinkage was larger with increasing the initiator quantities. Unfilled resins tended to show larger shrinkage.
Second, the shrinking stress in the open type cavity was measured during hardening. It was increased logarithmically with more initiator addition. The shrinking stress of unfilled resin was 2.6 times larger than the composite resin, and these were direct proportion.
Third, the surface profile of specimens were measured after hardening. The profile unfilled resin was changed a parabola to square with increasing the initiator quantities. These volume of the shrinkage was 8% of all, and the composite resin showed the volumetric decreasing with shallowing the parabola shape gradually.