Contraction stress of low-shrinkage composite materials assessed with different testing systems

Objectives. The contraction stress of a silorane-based material and a new low-shrinkage nanohybrid composite were compared to three conventional dimethacrylate-based resin composites using two different measuring systems. It was hypothesized that the silorane-based material and the low-shrinkage nanohybrid composite would exhibit lower contraction stress than dimethacrylate-based composites irrespective of measuring system. Methods. materials tested were Filtek Silorane LS (3M ESPE), Venus Diamond (Heraeus Kulzer), Tetric EvoCeram (Ivoclar Vivadent), Quixfil (Dentsply DeTrey), and Filtek Z250 (3M ESPE). Shrinkage stress was assessed using a stressstrain analyzer consisting of two opposing attachments, one connected to a load sensor and the other fixed to the device, or a system fixed to a universal testing machine with an extensometer as a feedback system. All specimens were light-cured with 20J/cm2; the contraction force (N) generated during polymerization was continuously recorded for 300s. Contraction stress (MPa) was calculated at both 40s and 300s. Data were statistically analyzed by three-way ANOVA and Tukey's post hoc test (a=0.05). Results. Venus Diamond exhibited the lowest stress under both experimental conditions. Stress values scored as follows: Venus Diamond<Tetric EvoCeram<Filtek Silorane LS<Quixfil<Filtek Z250 (p<0.05). Stress values measured with the stressstrain analyzer were significantly lower than those measured with the universal testing machine with feedback. Significance. The hypothesis was partially rejected because only Venus Diamond exhibited the lowest stress values among the tested materials. Contraction stress was higher for all composites when measured in a test system with a feedback. This study confirms that simply reducing the shrinkage does not ensure reduced stress development in composites. (C) 2010 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.