Objective To investigate the influenee of the consistency of resin composite and insertion techniques on the homogeneity of the Class I restorations.Methods Standardized Class I cavities were prepared in polymethyl methyacrylate(PMMA) blocks and restored with three resin composites (Prodigy,Tetric EvoCeram and Tetric Ceram HB)using either a packing or an injection technique by six operators.Then the restorations were sectioned longitudinally and inspected for the presence of porosities and voids with microscope.The consistence of the three resins was tested using an area method.Results There is little porosity in original resin.After insertion,large numbers of porosities were observed in restorations,with Tetric EvoCeram presented much more porosities(1137.1±365.0 for packing and 566.1 ±206.4 for injection)than Prodigy(241.0±116.1,195.8±28.7)and Tetric Ceram HB(193.1±35.8,156.3±33.0).Tetric Ceram HB showed the highest consistency,followed by Tetric EvoCeram and Prodigy.No linear correlation was found between the consistency of the composite and the porosity of their restorations.For Tetric EvoCeram.the restorations inserted with packing showed significant more porosity than that with injection.Contrastively,the restorations of Prodigy or Tetric Ceram HB presented no apparent difference for the two filling techniques.Conclusions The porosity in restoration was primarily created during the insertion.There was no linear correlation between the consistency of the composite and the porosity of their restorations.The porosity of composite resin is material-brand dependent.The influence of filling techniques on the porosity of restoration is depending on the composite used.