Polymerization shrinkage of densely-filled resin composites

A new group of restorative materials called "packable" composites has recen tly been introduced. These products are essentially highly-filled or densel y-filled hybrid resin composites. One of the many claims made about these m aterials is that they undergo less polymerization shrinkage than their conv entional counterparts. This in vitro investigation compared the amount of l inear shrinkage that occurs within a variety of densely filled resin compos ites (DFC) and conventional hybrid resin composites when cured with a visib le halogen light. Six DFC resins (Alert, Ariston, P60, Prodigy, Solitaire a nd Surefil) and two hybrids (TPH-Spectrum, Z100) were used in this study. D imensional change was measured in a linear direction using a calibrated lig ht microscope. Eighty samples of resin composite were tested, resulting in eight groups of 10 samples (N=10) each. The one-way ANOVA with Student-Newm an-Keuls post-hoc test was used to compare the shrinkage between groups, an d Pearson's Correlation was used to test the relationship between filler ch aracteristics and shrinkage. Alert and P-60 had significantly less shrinkag e than Solitaire, Ariston, Prodigy, Z-100 and TPH-S. Thus, the shrinkage va lues of some DFC resins were significantly less and others were no differen t from conventional hybrid resins. There is a moderate association between filler volume and shrinkage. Filler size and resin chemistry are other fact ors that may also effect shrinkage.