Effect of a resin-modified glass ionomer liner on volumetric polymerization shrinkage of various composites

Abstract

Objective. The aim of this study was to evaluate the volumetric polymerization shrinkage of a selection of composite resins alone, and in contact with a resin-modified glass ionomer (RMGI) liner. Methods. Volumetric polymerization shrinkage was measured for five different composite resins by means of the Watts and Cash deflecting disk method. Shrinkage measurements were determined for 300 s for each composite alone, and when placed over pre-cured RMGI liner. Each sample was placed within a brass ring fixed to a glass microscope slide. A linear vertical displacement transducer (LVDT) was brought into contact with a flexible glass coverslip placed over the composite sample. On curing, the contraction of the setting composite sample caused distortion of the coverslip, the resulting deflection being recorded via the LVDT by means of data-logging software. All RMGI samples were prepared at 85% relative humidity (RH) and 35°C. In all cases the composite was light-cured at ambient RH and 35°C. Results. Analysis of the data demonstrated statistically significantly less shrinkage for each composite when cured in contact with the set RMGI liner than when cured alone, at p<0.001. Significance. Use of an RMGI liner was found to significantly reduce volumetric polymerization contraction for all the light-curing composite resin restorative materials tested.