Bulk-fill Versus Conventional Composites: Microhardness at Increasing Depths
Objectives: Bulk-fill composites may provide more time-efficient placement, as well as reduced patient chair-time compared to their conventional counterparts. These materials are reported to have improved polymerization for greater depths, and can be placed in larger increments.The aim of this research was to measure microhardness of three representative bulk-fill composite materials and compare them to conventional composites produced by the same manufacturers. Methods: Composite coupons (5mmx5mmx2mm thick and 5mmx5mmx4mm thick) (N= 5 each) were made of the following resin materials: Tetric Evoceram® (TE) & Tetric Evoceram® BulkFill (TEB) (Ivoclar Vivadent, Inc, Amherst, NY); and Filtek™ Supreme Ultra (F) & Filtek™ BulkFill (FB) (3M, St. Paul, MN); Grandioso® (G) X-tra fil® (XF) (Voco America, Inc, Indian Land, SC). Samples were cured according to manufacturer instructions using a Bluephase20i (Ivoclar Vivadent Inc, Amherst, NY) broadband LED curing light (> 1000 mW/cm2). Samples were wet polished through 2.5 microns particle size grit. Knoop microhardness (Buehler Wilson Microhardness tester, Buehler, Lake Bluff, IL) values were obtained by applying a 50gr load for a 15 second dwell time. Triplicate measurements were taken every 200µ throughout the entire sample depth and averaged. Data were collected at three time points: immediately post-cure, following storage at 37C and 100% humidity for 24-hr and 30-days. Results were compared using ANOVA with post-hoc Tukey (α=0.05). Results: For 4mm samples, XF and F reached their maximum hardness value at T=0 and did not increase over time. TEB reached its highest value at 24-hr post-cure. Microhardness values in TE, G, and FB did not increase after 24-hr, however, significant increase was observed after 30-days post-cure.
For 2mm samples, XF and FB showed increased microhardness from T=0 to 24-hr, and reached their maximum at the 24-hr time point. G’s microhardness measured at 24-hr was statistically similar to values at T=0 and continued to increase to its maximum value at 30-days. For F, TE, and TEB, microhardness values reached maximum at T=0 and did not increase post initial cure. Conclusions: Microhardness values over time were material dependent, with some reaching maximum microhardness immediately after cure and other increasing over time, up to one month.