Interfacial integrity of bulk-fill resin composite restorations in deep Class-II cavities

This study evaluated the interfacial integrity of deep (6 mm) Class-II (OM/OD) restorations placed using different bulk-fill resin composites [Filtek (TM) Bulk Fill Flowable Restorative (BF) and Filtek (TM) Bulk Fill Posterior Restorative (BP) (3M ESPE, St. Paul, MN, USA)] of different increment thicknesses (2 or 4 mm). BP was used for capping in all cases, while Filtek (TM) Z250 Universal Restorative (3M ESPE) was used as the control material. Interfacial debonding was measured during curing through acoustic emission (AE), followed by image analysis using micro-computed tomography and scanning electron microscopy. Microhardness testing was also conducted to assess degree of conversion. Depth of cure was adequate in all restorations. Specimens with 4-mm thick first increment of BF, which had a higher shrinkage strain, produced most AE events and debonding. Thus, bulk filling of deep cavities using bulk-fill resin composites with a high shrinkage strain should be avoided.