Effect of humidity on the volumetric polymerization shrinkage of resin restorative materials

This study measured the volumetric polymerization shrinkage of three resin restorative materials under ambient (that is, room) relative humidity conditions and compared it with shrinkage occurring under a higher humidity condition that simulated the oral cavity. Small, semi-spherical specimens of a compomer, microfill composite, and flowable microhybrid composite were formed and light-activated using a halogen photocuring unit. The volumetric polymerization shrinkage of 15 specimens of each product was measured using a drop shape analysis unit for the relative humidity level of the ambient room (58.6 +/- 5.9%) and a higher humidity level that simulated the oral cavity (98.0 +/- 2.9%). Mean volumetric shrinkage values were calculated for each resin composite and the data were analyzed using a two-way analysis of variance (alpha = 0.05) to determine if significant differences existed between the amount of volumetric polymerization shrinkage that occurred under ambient room humidity conditions and the amount that occurred under simulated intraoral humidity conditions. Statistical analysis indicated that there was no significant difference (p = 0.17).