Shrinkage assessment of low shrinkage composites using micro-computed tomography

Objectives: The aim of this study was to quantify the polymerization volumetric shrinkage of one regular and two low shrinkage bulk fill composites in class I cavities with or without an adhesive layer, using three-dimensional (3D) micro-computed tomography (μCT). Methods: Class I cavity preparations (2.5 mm depth × 4 mm length × 4 mm wide) were standardized in 36 extracted human third molars, which were randomly divided in six groups (n = 6 each) as follows: Group VIT (regular composite without bonding agent); Group SDR (low shrinkage flowable composite without bonding agent); Group TET (low shrinkage composite without bonding agent); Group VIT/P (regular composite with bonding agent); Group SDR/X (low shrinkage flowable composite with bonding agent); TET/T (low shrinkage composite with bonding agent). Each tooth was scanned via μCT at cavity preparation, immediately after cavity filling, and after light-curing. Acquired μCT data were imported into Amira software for analysis and volume values evaluated between steps from cavity preparation until light-curing. Results: Both low shrinkage composites showed a significantly less volumetric shrinkage than VIT. The use of dental adhesive significantly decreased the average volumetric contraction similarly for the three composites, by about 20%. Conclusion: Both low shrinkage composites showed less volumetric polymerization contraction than the regular composite. The use of dental adhesive decreased the total volumetric shrinkage for all evaluated composites.