Bonding Mechanism of Bioactive Dentin Substitute Material to Composite Resin

Objectives: Bioactive dentin substitute(e.g. Biodentine^®) can served as promising pulp capping material recently. However, the bonding to composite resin remains challenge. We aim to explore the bonding mechanism by shear bond strength (SBS) test according to the phase changes of Biodentine crystallization.
Methods: We analyzed phase changes of Biodentine^® at various time intervals (1d, 2d, 3d, 7d and 14d) in dd-water/HBSS immersion by XRD (2θ: 20–60 degree) and SEM examinations. Seventy-two Biodentine^® specimens were prepared (4-mm diameter/ 2-mm height) for SBS test. After 7d storage, the specimens were randomly divided into two groups, with additional Monobond Plus primer or not. Each group was allocated into 3 subgroups (n=12 for each): Prime & Bond NT^TM (PNT), Single Bond Universal (SBU) and Xeno V (Xeno), for bonding to composite resin (SDR^TM). SBS was measured using universal testing machine(crosshead speed:1 mm/min).The data was analyzed with one-way ANOVA and post-hoc Tukey’s test (α=0.05). We investigate fractography under SEM examination.
Results: XRD showed main components were CaCO₃, ZrO₂ and Ca₃SiO₅; the intensities increased in first 3d and became stable after 7d. Biodentine^® treated with additional primer (10-MDP contained) exhibited significant higher SBS (p < 0.05) except PNT subgroup (SBU: 17.5 ± 3.6 vs. 10.8 ± 2.3; Xeno: 12.9 ± 3.8 vs. 9.2 ± 1.4 MPa; PNT: 12.2 ± 4.2 vs. 10.8 ± 4.4 MPa). SEM indicated most specimens of failure mode were mixed failure in Biodentine^® side. No specimen failed cohesively in composite resin. The unfilled porous among CaCO₃ and Ca₃SiO₅ grains might be the risk area of fracture.
Conclusions: Zirconia crystals grew in Biodentine might be an impact for the bonding. Monobond Plus primer would enhance SBS, especially in SBU adhesive which also contains 10-MDP. However, the benefit did not appear in etch-and-rinse PNT adhesive.