Direct and semi-direct resin composite restoration in large cavity preparations : analysis of dentin bond strength stability and bottom/top microhardness ratio in a cavity model

[Abstract] To evaluate the influence of the restorative approach and aging time on dentin bond strength (BS), failure mode (FM), and bottom/top microhardness ratio (B/T) in a large dentin cavity model. A total of 102 bovine incisors were used to produce models of conical dentin cavities (4.0 mm thickness * 4.8 mm top diameter * 2.8 mm bottom diameter), which were restored using semi-direct filling (SDF) (Filtek(TM) Z250 XT + Scotchbond(TM) Universal/RelyX(TM) Ultimate luting system), direct bulk filling (DBF) (Filtek(FM) One Bulk Fill), and direct incremental filling (DIF) (Filtek(TM) Z250 XT) techniques. B/T, BS, and FM (n=17) were analyzed in a microhardness tester, a universal testing machine, and a stereomicroscope, respectively, after 24 h and 6 months of water storage. BS and B/T data were analyzed using two-way ANOVA/Tukey post-hoc test (p0.05). Although all restorative approaches provided similar B/T, the semi-direct technique showed better performance on the material bond strength to dentine in large cavities.