Physical Properties Assessment of Flowable Bulk Fill Resin Composites

Objectives: The achievement of predictable and long lasting restorations in posterior teeth had always been a major objective. With the development of bulk fill resins, claimed to be used in large increments and to generate lower polymerization shrinkage and stresses, simpler and reliable results should be possible, mainly with flowable composites. The objectives of the present study were to assess the depth of cure, volumetric shrinkage and shrinkage stress of different resin composites (Filtek Z350XT-Z3XT, Filtek Z350XT Flow-Z3F, Surefill SDR-SDR, Xtra Base-XB and Filtek Bulk Fill Flowable-FBF).
Methods: For depth of cure, longitudinal Knoop microhardness was performed in the specimens (n=8) right after 20s light curing, using a 50g weight during 20s. Values equal or higher than 80% of surface microhardness were considered as adequate. For volumetric shrinkage, seven specimens of composite (4x4x4mm) were scanned in micro-CT before and right after 20s light curing, the images were processed and analyzed for changes in dimensions. For shrinkage force assessment, the polymerization stress was measured through deformation of a load cell adapted in an Universal testing machine, up to 300s after polymerization of the composites with 12/24mm³ (n=7). Data was evaluated through one-way ANOVA (volumetric shrinkage and depth of cure), three-way ANOVA (shrinkage force) and Tukey’s test, all with p<0.05.
Results: The results showed higher values of depth of cure for SDR(6.93±0.41), followed by XB(6±0.88) and FBF(5.62±0.35), with Z3F(3.62±0.23) and Z3XT(2.62±0.23) showing the lowest values. Considering the polymerization shrinkage, similar values were observed for all groups: FBF(3.34±0.59), XB(3.11±0.16), SDR(3.36±0.62), Z3F(3.84±0.23) and Z3XT(3.07±0.61). Regarding polymerization stress, respectively 12 and 24mm³ after 300s: FBF(6.32±0.43/8.7±0.65), XB(6.3±0.25/9.24±0.62), SDR(4.63±0.25/5.43±0.44), Z3F(10.56±0.49/13.39±0.41), and Z3XT(5.67±0.21/9.97±0.43), bulk fill composites generated equal/lower stress when compared with conventional composites.
Conclusions: It can be concluded that the tested bulk fill composites were able to be polymerized in large increments (>5mm), while presenting equal/lower volumetric shrinkage and shrinkage stress.