Abstract:

BACKGROUND: Glass fiber reinforced plastic (GFRP) has been introduced as an alternative root canal post material for conventional metal cast- and prefabricated posts, but the unique shape and small sizes of the commercial GFRP posts has made the mechanical evaluations difficult using conventional bending tests.
OBJECTIVE: To evaluate the bending properties of three types of commercial GFRP posts using a sensitive cantilever test.
METHODS: Three commercial GFRP posts with different diameters were used in this study, and tested posts were divided into four groups based on diameter ranges (0.9-1.0 mm, 1.2-1.25 mm, 1.4-1.5 mm and 1.6 mm). Bending specimens were prepared by embedding half of each post into resin cement in a mould, and then fixed into the jig and subjected to a cantilever test in a texture analyzer with a load speed of 6 mm/min.
RESULTS AND CONCLUSION: Typical load-deflection curves of the GFRP posts included a number of sharp decreases of load after the proportional limits and before fractures. The peak load before the first decrease of load was defined as a pop-in load, and used as an index of an important mechanical property. Debending of the fibers from the matrix and crack initiation after the pop-in load appeared in scanning electron microscopy photomicrographs of the GFRP post surfaces. The maximum bending load tended to increase with an increase of post diameter; however, the bending strength decreased with an increase in diameter. The elastic modulus of GFP and FBK posts decreased significantly with an increase of post diameter. The bending strength and elastic moduli of FBK posts with a diameter of 1.0 mm were the highest among the tested posts. The bending properties of GFRP posts may be evaluated under clinical situation using a sensitive cantilever test. The behavior of pop-in load was a useful index of evaluation of clinical prognoses of GFRP posts.