Flow characteristics and film thickness of flowable resin composites

Flowable resin composites have been recommended for many clinical uses and have been formulated in a variety of compositions and viscosities to meet various uses. This study compared the variation in viscosity of flowable resin composites using the ADA Flow Test and measured film thickness with a test to simulate flow during cementation. The film thickness test for the flowable resin composites was performed at three different seating pressures to simulate pressure variation during seating of porcelain veneers, one of the potential uses of flowable resin composites that may favor a lower viscosity. The following flowable resin composites were evaluated: Revolution, StarFlow, Aeliteflo LV, Aelite, Flow-It, FloRestore, Versaflo, Durafill Flow and Tetric Flow, with Nexus2, a composite luting resin used as a control. Flow characteristic measurements suggest that resin composites may be divided into high flow (StarFlow, Revolution, Aeliteflo LV), medium flow (FloRestore, Durafill Flow, Flow-It) and low flow (Tetric Flow, Versaflo, Nexus2, Aelite) groupings. The film thickness measurements agreed with the ADA flow test, except for two exceptions. Durafill Flow resin composite had a higher film thickness than expected based on the ADA flow test. Also, Aeliteflo unexpectedly had a lower film thickness. At the lowest seating pressure (.016MPa) tested, eight out of the nine resin composites tested as well as the control luting resin had a film thickness greater than the 25 microns used as the clinical standard for cement film thickness. However, at the highest seating pressure (.038 MPa) tested, only two and the control, Versaflo, Durafill Flow and Nexus2, had film thicknesses significantly greater than 25 microns. The highly filled Nexus2 luting resin had the highest film thickness at all seating pressures.