The effect of viscoelastic behavior of resin-based dental materials on the resin-dentin shear bond strength.

Objectives: 1) To clarify the effect of static or dynamic viscoelastic behavior of dentin and three resin-based dental materials on resin-dentin interfacial shear bond strength. 2) To investigate the influence of resin-based dental materials' viscoelastic behavior on residual stress at resin-dentin interface using finite element analysis (FEA).

Methods: Resin-dentin bonded specimens of three resin-based dental materials underwent monotonic compression, static and dynamic bulk compressive creep tests. Then shear bond strength, failure modes, and interface morphology were assessed. Additionally, polymerization shrinkage (s) and Young's modulus (E) for the materials were determined using buoyancy method and dynamic mechanical analysis (DMA), respectively. Cylindrical specimens underwent static/dynamic creep tests to collect stress-strain data. Finally, FEA was employed to assess the residual stress distribution at resin-dentin interface with/without creep tests.

Results: 1) Compared to monotonic compression, both static and dynamic creep significantly increased resin-dentin bond strength (p < 0.05), with dynamic creep superior. 2) Monotonic compression primarily caused mixed adhesive and cohesive failures, while bulk compressive creep tests reduced adhesive failure and increased cohesive failure. 3) Monotonic compression caused more hollow dentin tubules and pulled-out resin tags, whereas bulk compressive creep tests revealed resin tags inside tubules and cracks between resin and dentin. 4) FEA indicated stress concentration at margins of the bonded area, with the resin adhesive layer experiencing the highest stress. After bulk compressive creep tests, stress distribution became more uniform, and residual stress decreased by 50 % or more.

Conclusions: Bulk compressive creep improves resin-dentin bond strength by facilitating interfacial stress relaxation. The resin-based dental materials' viscoelastic behavior mitigates polymerization shrinkage stress, enabling effective stress relaxation at resin-dentin interface.

Clinical Significance: During direct restoration process, resin-based dental materials with appropriate viscoelastic properties can effectively reduce polymerization shrinkage stress. This, in turn, promotes efficient stress relaxation at the resin-dentin interface and enhances bonding performance.