Clinical performance and chemical-physical properties of bulk fill composites resin -a systematic review and meta-analysis. 
The objective of this study was to perform a meta-analysis of clinical and laboratory studies to compare the performance of bulk-fill and conventional composite resins in terms of polymerization shrinkage, polymerization stress, cusp deflection, marginal quality, degree of conversion, microhardness, flexural strength, fracture strength and clinical performance.  One hundred three articles were included in this study, and the Peto method was used to compare the bulk-fill and conventional composites using the RevMan software.  Searches were performed in the PubMed and Scopus databases.  Laboratory studies and randomized clinical trials comparing one of the previous detailed outcomes between bulk-fill and control composites were included.  The bulk-fill composite resins showed less shrinkage, polymerization stress, cusp deflection and microhardness than conventional composites, while both materials presented a similar marginal quality, flexural strength and fracture strength.  Also, bulk-fill materials with regular viscosity showed similar shrinkage.  The conversion of bulk-fill materials with flowable consistency were similar to conventional composite resins with a thickness of up to 2mm and greater than conventional composites with a thickness greater than 2mm.  Despite these in vitro differences, the clinical performance of bulk-fill and conventional composite resins was similar in randomized clinical trials, with one to ten years of follow up.  In conclusion, the bulk-fill materials show better or similar performance to the conventional materials in clinical trials and laboratory studies in terms of volumetric shrinkage, polymerization stress, cusps deflection and marginal quality, with the only exception being the lower level of microhardness observed for bulk-fill composites with thickness up to 2mm.