Fracture resistance and reliability of new zirconia posts

Abstract

Statement of problem The radicular portion of zirconia endodontic posts often need to be reshaped to achieve a definitive form and may be airborne-particle abraded to improve adhesion during luting. Therefore, the surface of the tetragonal zirconia ceramics may be transformed and damaged, influencing the mechanical properties of the material. Purpose This study compared the fracture resistance of prefabricated zirconia posts with a new retentive post-head after different surface treatments. Material and methods Experimental zirconia posts of 2 different diameters, 1.3 mm and 1.5 mm, were produced from commercially available zirconia powder. A cylindro-conical outline form was used for the root portion of the system and a post-head with 3 retentive rings was designed. Sixty posts of each diameter were divided into 3 groups (n=20). Group 1 was ground with a coarse grit diamond bur; Group 2 was airborne-particle abraded with 110-μm fused alumina particles, and Group 3 was left as-received (controls). Posts were luted into the root-shaped artificial canals with the Clearfil adhesive system and Panavia 21 adhesive resin luting agent. The posts were loaded in a universal testing machine at an inclination of 45 degrees with the constant cross-head speed of 1 mm/min. The fracture load (N) necessary to cause post fracture was recorded, and the statistical significance of differences among groups was analyzed with 1-way ANOVA followed by the Fischer LSD test (α=.05). The variability was analyzed using Weibull statistics. Results Load to fracture values of all zirconia posts depended primarily on post diameter. Mean fracture loads (SD) in Newtons were 518.4 (±101.3), 993.6 (±224.1), and 622.7 (±110.3) for Groups 1 through 3, respectively, for thicker posts, and 385.9 (±110.3), 627.0 (±115.1), and 451.2 (±81.4) for Groups 1 through 3, respectively, for thinner posts. Airborne-particle-abraded posts exhibited significantly higher resistance to fracture ( P<.05) than those in the other 2 groups for diameters 1.3 mm and 1.5 mm. Grinding reduced Weibull modulus compared with controls, and the values were 4.1 and 6.5 for thicker and thinner posts, respectively. Conclusion Within the limitations of this study, the results suggest that grinding leads to a significant drop in load to fracture of zirconia posts, whereas airborne-particle abrasion increased the fracture load.