Factors Influencing the Dimensional Change in Light-cured Restorative Material : Effect of Specimen Storage Conditions on Polymerization Shrinkage

Abstract

The objective of this study was to examine the effect of specimen storage conditions on the dimensional change of light-cured restorative materials after curing. Ten commercially available conventional composite resins, six different products of flowable type composite resins and three different products of polyacid-modified composite resins were examined. The tapered cylindrical composite resin specimens were prepared using a stainless steel mold and the polymerization shrinkage of specimens after light curing was measured according to the method reported by Bowen et al. The specimens were weighed after determination of curing shrinkage. Then, the specimens were kept for 7 days in either air at 23±2℃ and 50±5% relative humidity or a moisture chamber at 37±2℃ and 95±5% relative humidity. The amounts of dimensional change and the weight of specimens were mensured again after storage of 7 days. In addition, the inorganic filler content in specimens was estimated by burning the specimens at 700℃ in a furnace. All the light-cured restorative materials shrank by light-curing. When the specimens were kept after curing in the moist condition, the amount of contraction was suppressed due to the absorption of water. A positive correlation was found after water sorption between the amounts of changes in weights and in dimensions of specimens. Changes in contraction of specimens after light-curing by water sorption appeared to be related to the nature of the matrix resin in composite resin.