Polymerization shrinkage stress of modern condensable resin composites

Objectives: To evaluate the polymerization shrinkage stress (PSS) of modern low shrinkage resin composites and to discuss methodological aspects.

Methods: The PSS test was performed using 6mm diameter PMMA rods as bonding substrates (high compliance system). The rod surfaces were sandblasted prior to adhesive bonding. An extensometer was used to control the cylindrical specimen height at 1mm. PSS measurements (n=10) were carried out in a universal testing machine. The data were analyzed using ANOVA (S-N-K post hoc, a=0.05). Eleven commercial materials were selected for the test: CeramXMono (CXM), ClearfilMajestyEsthetic (CME), ClearfilMajestyPosterior (CMP), EsteliteSigmaQuick (ESQ), FiltekSupremeXTE (FIS), GrandioSO (GRA), Kalore (KAL), SDR (SDR), TetricEvoCeramBulk (TEB), TetricEvoCeram (TEC), VenusDiamond (VED).

Results: The PSS [in MPa] for the evaluated resin composites is 0.94 ± 0.11 (CMP) a, 1.13 ± 0.11 (ESQ) b, 1.16 ± 0.17 (FIS) b, 1.19 ± 0.09 (VED), 1.20 ± 0.10 (CME) b, 1.21 ± 0.06 (KAL) b, 1.23 ± 0.11 (TEC) b, 1.26 ± 0.09 (GRA) b, 1.37 ± 0.06 (SDR) c, 1.51 ± 0.12 (CXM) c, 1.56 ± 0.06 (TEB) c (small letters indicate statistically homogenous subgroups).

Conclusions: Generally all materials show low PSS values mainly due to the high compliance of the measuring system. The results need to be discussed carefully since some of the materials might produce a different outcome in a low compliance setup.  The data shown here should be used for internal comparisons and is strongly related to the used method and experimental factors.