Polymerization shrinkage ratio and force of various core composites

Objectives: Polymerization shrinkage of resin composite is in the focus of research in resin composite restoratives. At post and core restoration, there is concerned that polymerization shrinkage force can weaken the interfacial bond, affecting bond strength to the tooth and post surface. The aim of this study was to examine the polymerization shrinkage ratio and force of various core composites.

Methods: Four dual-cured core composite resins [Experimental core composite (UCA-106, GC corporation), Luxacore-Dual smartmix (LU, DMG), Build-IT FR (BI, Pentron clinical technologies, LLC) and Clearfil DC Core Automix (DC, Kuraray Medical inc.)] were examined. The polymerization shrinkage ratio of core composite was determined in difference of density between before and after-cured through density determinations in accordance with the buoyancy method (Archimedes' principle). The polymerization shrinkage force was measured as tensile load generated at polymerization of core composite using universal testing machine with special apparatus for measuring shrinkage force. The test of polymerization shrinkage force was performed with the volume of 1.5ml each core composite, height of specimen was 3mm and contact area linking to load cell was isolated in 4mm diameter. Curing method of core composites was light-curing and self-curing. Statistical analysis was performed using one-way ANOVA (p-value<0.05).

Results: Mean values of polymerization shrinkage ratio and force by light-curing including standard deviations were shown as follows; (tests per material; n=5).

Polymerization shrinkage ratio and force by light-curing for UCA-106 and DC was significantly lower than those for LU and BI (p<0.05).

Conclusion: Polymerization shrinkage ratio and force were different between various core composites. UCA-106 and DC had significantly lower polymerization shrinkage ratio and force compared to LU and BI.