Shrinkage Assessment of Regular and Flowable Bulk-fill Composites Using Micro-computed Tomography

Objectives: The aim of this study was to compare and characterize the volumetric polymerization shrinkage and gap formation of five different composites (one regular and four bulk fill) in class I cavities using three-dimensional (3D) micro-computed tomography (μCT).
Methods: Standardized class I cavity preparations (4 mm depth X 4 mm length X 4 mm wide for Bulk Fill composites and 2.5 mm depth X 4 mm length X 4 mm for Regular Composites) were prepared in 30 extracted caries-free human third molars, which were randomly divided into 5 groups (n=6) according to the different filling materials: G1 – regular composite Filtek Z100 (Z100 - 3M ESPE); G2 – high viscosity EvoCeram Bulk Fill (EB - Ivoclar Vivadent); G3 – low viscosity Evoflow Bulk Fill (EF - Ivoclar Vivadent); G4 – high viscosity Filtek Bulk Fill (FB - 3M ESPE); and G5 – low viscosity Filtek Bulk Fill Flow (FF - 3M ESPE). Each tooth was scanned via μCT at 3 different times: after cavity preparation, immediately after cavity filling, and after light-curing. Acquired μCT data was imported into a 3D-image reconstruction software (Amira, FEI Visualization Group) for analysis in volumetric changes. Data were submitted to one-way analysis of variance and post-hoc comparisons.
Results: The regular composite Z100 (G1) obtained the highest percentages of volumetric shrinkage (3.96%), although not significantly different than the flowable bulk fill composites EF (G3 – 2.75%) and FF (G5 – 3.50%). The high viscosity bulk fill composites EB (G2 – 2.31%) and FB (G4 – 2.40%) showed the lowest percentages of volumetric shrinkage, although not significantly different than the flowable bulk fill composite groups G3 and G5.
Conclusions: Volumetric polymerization shrinkage is material dependent, and high viscosity bulk fill materials showed better results regarding this aspect. Shrinkage was mostly observed at occlusal surface.