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 fasten and simplify the restoration process, a new class of composite resins, called the bulk fill composite resins have been introduced, which has been claimed to achieve a depth of cure (DOC) of 4 mm without affecting the properties of the material.

The Purpose of this study was to investigate the effect of different shades, thicknesses and viscosities on the DOC of bulk-fill composites.

Four bulk-fill composites [FiltekTMBulkfill Flowable (FBF), FiltekTM Bulkfill posterior (FBP), Tetric N-Flow bulkfill(TNF), Tetric N-Ceram bulkfill(TNC)] and a conventional composite, FiltekTM Z250XT Universal (FZ) were evaluated. samples (n=5) were made using two different shades( light and dark), thicknesses (2 and 4mm) and viscosities (flowable and sculptable). Microhardness was conducted on top and bottom surface using Vickers microhardness tester and DOC calculated as the bottom/top ratio. Statistical analysis was done using a mannwhitney test at p < 0.05.

DOC ranged between 52-95%. FBF composite exhibited the lowest overall hardness numbers. At 2-mm thickness, all the samples achieved an appropriate DOC. However, at 4-mm 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, DOC of FB )dark and light shades (and DOC of TN (light shade( were different in the flowable type from the sculptable type.

Shade and viscosity influence DOC of bulk-fill composites at 4-mm depths. For bulk-fill composites, 20s light curing appears insufficient for 4mm bulk-fill placement.