factors affecting marginal integrity of class ii bulk-fill composite resin restorations

Background. bulk-fill composite resins are a new type of resin-based composite resins, claimed to have the capacity to be placed in thick layers, up to 4 mm. this study was carried out to evaluate factors affecting gap formation in cl ii cavities restored using the bulk-fill technique. methods. a total of 60 third molars were used in this study. two cl ii cavities were prepared in each tooth, one on the mesial aspect 1 mm coronal to the cej and one on the distal aspect 1 mm apical to the cej. the teeth were divided into 4 groups: a: the cavities were restored using the bulk-fill technique with filtek p90 composite resin and its adhesive system and light-cured with quartz tungsten halogen (qth) light-curing unit. b: the cavities were restored similar to that in group a but light-cured with an led light-curing unit. c: the cavities were restored using the bulk-fill technique with x-tra fil composite resin and clearfil se bond adhesive system and light-cured with a qth curing unit. d: the cavities were res-tored similar to that in group c but light-cured with an led light-curing unit. the gaps were examined under a stereomi-croscope at ×60. data were analyzed with general linear model test. in cases of statistical significance (p<0.05), post hoc bonferroni test was used for further analyses. results. the light-curing unit type had no effect on gap formation. however, the results were significant in relation to the composite resin type and margin location (p<0.001). the cumulative effects of light-curing unit*gingival margin and light-curing unit*composite resin type were not significant; however, the cumulative effect of composite rein type*gingival mar-gin was significant (p=0.04) conclusion. x-tra fil composite exhibited smaller gaps compared with filtek p90 composite with both light-curing units. both composite resins exhibited smaller gaps at enamel margins.