Flowability of composites is no guarantee for contraction stress reduction

Objectives. The purpose of this study was to measure the contraction stress development of three flowable resin-composite materials (Grandio Flow, VOCO GmbH, Cuxhaven, Germany; Tetric Flow, Ivoclar Vivadent, Schaan, Liechtenstein; Filtek Supreme XT Flowable Restorative, 3 M ESPE, ST. Paul, MN, USA) and an universal micro-hybrid composite resin (Filtek Z250, 3 M ESPE, St. Paul, MN, USA) during photopolymerization with a halogen curing light, using a novel stress-measuring gauge. Methods. Curing shrinkage stress was measured using a stress-analyzer. Composites were polymerized with a halogen curing unit (VIP, Bisco Inc., Schaumburg, IL, USA) for 40 s. The contraction force (N) generated during polymerization was continuously recorded for 180 s after photo-initiation. Contraction stress (MPa) was calculated at 20 s, 40 s 60 s, 120 s and 180 s. Data were statistically analyzed. Results. Filtek Supreme XT Flowable Restorative exhibited the highest stress values compared to other materials (p < 0.05), while the lowest values were recorded with Tetric Flow (p < 0.05). Tetric Flow was also the only flowable composite showing stress values lower than the conventional composite Filtek Z250 (p < 0.05). Significance. Flowable composites investigated with this experimental setup showed shrink-age stress comparable to conventional resin restorative materials, thus supporting the hypothesis that the use of flowable materials do not lead to marked stress reduction and the risk of debonding at the adhesive interface as a result of polymerization contraction is similar for both type of materials. (C) 2008 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved