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Influence of Cement Thickness on Adhesive Properties of CAD/CAM Fabricated One-piece Fiber Post-and-core: Micro Push-out and Finite Element Analysis Study

Jing Su,Qing Cai*,Zhixin Huang,Hongcheng Zhang,Xuliang Deng*,Xiaoping Yang

This study is to test if the bond strength between fiber post and dentin is inversely relative to the thickness of adhesive cement, basing on a kind of CAD/CAM fabricated one-piece fiber post-and-core (OPFPC), which was designed for individual-based endodontical treatment.

Twenty-seven noncarious single-canal extracted human teeth were endodontically treated, with the crown being removed perpendicular to the tooth long axis. OPFPC specimens with different designs in the diameter of the post were fabricated with the aid of CAD/CAM and fitted into corresponding root canals, accordingly, cement thicknesses between the post and the dentin were set as ~300, ~150 and ~10 µm, respectively. Samples were prepared by sectioning the OPFPC-fitted tooth perpendicularly to tooth long axis, and subsequently submitted to micro push-out test. By using Finite Element Analysis (FEA), the Contact Press Stress (CPS) and Maximum Principal Stress (MPS) in the OPFPC-fitted tooth with different cement thicknesses were calculated.

The micro push-out test proved that the bond strength between fiber post and dentin increased apparently as the cement thickness decreasing. A common failure mode found in the test was the damage occurring at the Adhesive-Dentin (AD) interface, but the Adhesive-Post (AP) interfacial failure mode was likely to be observed when the cement was relatively thick. FEA modelling indicated that interfacial stress deriving from CPS on both AD and AP interfaces increased along with thicker adhesive layer, and the MPS distribution area was reduced on both the interfaces when the cement thickness was increased. All the data suggested that better bond condition was confirmed at the thinner adhesive layer between the fiber post and the dentin. CAD/CAM fabricated OPFPC, which could fit the root canal perfect, thus demonstrated advantages over the conventional fiber post for clinical endodontical therapy.