The Effect of Shade and Thickness on the Depth of Cure of Bulk-Fill Composites with Different Viscosities

Statement of the problem: in an attempt to enhance and simplify the restoration process, a new class of composite resins, called the bulk fill composite resins have been introduced. it is claimed that a depth of cure (doc) of 4 mm can be achieved without affecting the prop-erties of this material. purpose: the purpose of this study was to investigate the effect of different shades, thicknesses, and viscosities on the doc of bulk-fill composites. materials and method: in this experimental study, four bulk-fill composites [filtek™ bulk fill flowable (fbf), filtektm bulk fill posterior (fbp), tetric® n-flow bulk fill (tnf), tetric® n-ceram bulk fill (tnc)] and a conventional composite, filtek™ z250 xt uni-versal (fz) were evaluated. the samples (n=5) were made using two different shades (light and dark), thicknesses (2 and 4mm), and viscosities (flowable and sculptable). microhard-ness test was conducted on top and bottom surface using vickers microhardness tester and doc was calculated as the bottom/top ratio of yielded scores. statistical analysis was done using a mann whitney test at p< 0.05. results: doc ranged between 52-95%. fbf composite exhibited the lowest overall hard-ness numbers. at 2-mm thickness, all the samples achieved an appropriate doc. however, at 4mm thickness, only the light shades for fbf and tnf samples achieved a doc very close to 0.8. at 4-mm thickness, the light shades for fbf, tnf and fz samples exhibited significantly higher doc compared to dark shades. for 4-mm-thick samples, the doc of filtektm bulk fill (dark and light shades ( and the doc of tetric® bulk fill (light shade) were different in flowable type from the sculptable type. conclusion: the shade and the viscosity of bulk-fill composites influence their doc at 4-mm depths. moreover, 20 seconds of light curing appears insufficient for 4mm thickness of bulk-fill composite.