Fracture toughness, vibration modal analysis and viscoelastic behavior of Kevlar, glass, and carbon fiber/epoxy composites for dental-post applications

The use of flexible dental posts concentrates the stress at the dentin and the use of stiff posts increases the stress at the interface. Efforts were directed toward introducing inhomogeneous materials for resolving the disadvantages of both flexible and stiff posts. The main objective of this study was to develop three different fiber/epoxy composite posts. These composites were fabricated using carbon, glass, and Kevlar fibers. Characterization tests were conducted. In the tensile tests, the carbon, glass and Kevlar fiber composites exhibited tensile strengths of 200%, 91%, and 40% of the stainless-steel tensile strength, respectively, and exhibited stiffness values of 62%, 33%, and 12% of the stainless-steel stiffness. The carbon fiber/epoxy composite have a fracture toughness close to that of aluminum alloy. Vibration modal analysis indicated that the frequency response of the carbon fiber composite was lower than those of the glass and Kevlar composites. The highest tensile strength, storage moduli, and stiffness were recorded for the carbon fiber composites and the lowest were for Kevlar fiber composite. The low stiffness and strength of the Kevlar composite are attributed to the fact that Kevlar fibers had lower wettability with epoxy resin than both glass and carbon fibers. Moreover, the Kevlar fiber composite exhibited higher delamination. However, the stiffness and strength of Kevlar made its composite more sensitive than the other composites to free vibrations generated by a simple force induced by a hammer. Based on the results, the carbon fiber/epoxy composite has appropriate characteristics for application in new dental posts.