Polymerization profile analysis of resin composite dental restorative materials in real time

OBJECTIVES: In this study, the hypothesis that the polymerization shrinkage profile of "low shrinkage" non-methacrylate based composite; Silorane and "low shrinkage" high molecular mass methacrylate based composite; Kalore is not different from that of three conventional methacrylate based composites (Gradia Direct X, Filtek Supreme XT and Beautifil II) was tested.

METHODS: Five commercially available composites were analysed: one "low shrinkage" non-methacrylate based composite (Silorane); one "low shrinkage" high molecular mass methacrylate based composite (Kalore) and three conventional methacrylate based composites (Gradia Direct X, Filtek Supreme XT and Beautifil II). Polymerization shrinkage was measured using an electromagnetic balance which recorded changes in composite buoyancy occurring due to volumetric changes during polymerization. This instrument allowed real time volumetric shrinkage measurements to be made at 40 ms intervals.

RESULTS: All five resin composites demonstrated a similar volumetric shrinkage profile during polymerization. The rate of shrinkage of all five composites decreased from t=0 at a rate approximating x=t. After 170 s the rate of shrinkage of all five composites was at or below 0.01%/s. During the initial 5s of light exposure Silorane and Kalore exhibited a significantly lower (p<0.05) rate of contraction relative to the three conventional methacrylate composites. After 640 s of analysis, Silorane exhibited a significantly lower (p<0.05) percentage volumetric contraction compared to the other four analysed materials.

CONCLUSIONS: The newly developed "low shrinkage" composites (Silorane, Kalore) in the present study demonstrated significantly lower (p<0.05) shrinkage rates and shrinkage volumes compared to the three conventional methacrylate composites. Investigation to identify whether polymerization shrinkage profile analysis is a good predictor of relative polymerization contraction stress levels generated by different composites, is warranted.

CLINICAL SIGNIFICANCE: Clinicians making a resin composite selection with the view to minimizing the clinical effects of polymerization shrinkage must consider the rate of polymerization as well as the total volumetric shrinkage of a composite. Silorane (non methacrylate composite) and Kalore (high molecular mass methacrylate composite) have the ability to exhibit lower shrinkage rates and lower shrinkage volumes compared to conventional methacrylate composites.