Push-out Bond Strength of Bulk-Fill Composites Used as Intracanal Anchorage Material

Purpose: Evaluation of different composites with varying viscosity for their suitability as intracanal anchorage (ICA) materials using push-out bond strength testing.
Materials and Methods: 48 human maxillary incisors were root filled, crowns partially removed except one residual wall, and distributed into four groups (n = 12), according to one of the following ICA composites: Ormocer (AFx), preheated composite (VB), core build-up (RDC) or flowable (SDR). A 4 mm deep root canal enlargement was prepared using Gates Glidden burrs, and hard tissues were conditioned using a universal adhesive in etch-and-rinse mode. Intracanal cavities were filled using the groups’ specific ICA material and a nanohybrid composite (GrandioSO, VOCO) for crown reconstruction. Two samples per group were scanned using phase-contrast-enhanced µ-computer tomography (PCE-CT). The remaining samples were thermo-mechanically loaded (TML), and push-out bond strengths and fracture patterns of ICA materials were analyzed.
Results: Push-out bond strengths were significantly affected by ICA materials (P = 0.001) and location inside the root canal (P 0.005; generalized estimating equations). VB showed a significantly lower bond strength (13.5MPa ± 5.3MPa) compared to RDC (19.6MPa ±7.6MPa) and AFx (21.4MPa ±7.6MPa), but did not differ significantly from SDR (20MPa ± 10.3MPa). All groups demonstrated predominantly adhesive failures between the composite and dentin (P 0.05; Chi-square test). µ-CT scans indicate material-dependent localization and quantity of voids.
Conclusion: The survival rates after TML and the push-out bond strength values indicate a sufficient bonding of all ICA materials. Frequently occurring voids highlight problems of application and the effects of materials’ viscosity on void formation and bond strength. Keywords: 3D analysis, adhesive/material interface, bulk-fill composite, intracanal anchorage, micro-CT, post endodontic restoration, push-out bond strength, porosity