Polymerization shrinkage of densely-filled resin composites.

A new group of restorative materials called "packable" composites has recently been introduced. These products are essentially highly-filled or densely-filled hybrid resin composites. One of the many claims made about these materials is that they undergo less polymerization shrinkage than their conventional counterparts. This in vitro investigation compared the amount of linear shrinkage that occurs within a variety of densely filled resin composites (DFC) and conventional hybrid resin composites when cured with a visible halogen light. Six DFC resins (Alert, Ariston, P60, Prodigy, Solitaire and Surefil) and two hybrids (TPH-Spectrum, Z100) were used in this study. Dimensional change was measured in a linear direction using a calibrated light microscope. Eighty samples of resin composite were tested, resulting in eight groups of 10 samples (N=10) each. The one-way ANOVA with Student-Newman-Keuls post-hoc test was used to compare the shrinkage between groups, and Pearson's Correlation was used to test the relationship between filler characteristics and shrinkage. Alert and P-60 had significantly less shrinkage than Solitaire, Ariston, Prodigy, Z-100 and TPH-S. Thus, the shrinkage values of some DFC resins were significantly less and others were no different from conventional hybrid resins. There is a moderate association between filler volume and shrinkage. Filler size and resin chemistry are other factors that may also effect shrinkage.