Thermal and cyclic loading of endodontic posts

The intent of this study was to determine pullout (shear) strength of carbon and stainless steel serrated posts from teeth. The tooth-posts groups were controls, thermal-cycled, load-cycled (load applied at either a 45 degrees angle or along the long axis of the post), and thermal- and load-cycled. Human extracted third molars were embedded in denture acrylic. Post space was prepared and the posts cemented with a resin cement according to manufacturer's instructions. The testing was in tension at a loading rate of 2 mm/min. The pullout (shear) strengths (MPa+/-SD) for the carbon posts were: controls 6.1+/-3.3; load-cycled 4.3+/-2.2; and thermal-cycled 4.2+/-2.2. The thermal-cycled and then load-cycled carbon posts all fractured during testing and were unable to be evaluated for shear strength. The pullout (shear) strengths (MPa+/-SD) for the stainless steel posts were: controls 6.6+/-2.9; load-cycled 7.1+/-3.2; thermal-cycled 4.8+/-2.0; and thermal load-cycled 6.8+/-3.5. The statistical analysis indicated no significant difference in the pullout (shear) strength between any of the post groups tested. Two different operators then prepared specimens using carbon posts abraded with 50 microm alumina and non-abraded carbon posts. The alumina abrasion caused a decrease in the post bond strength with the alumina particles impinging on the carbon fibers resulting in their fracture. The significant difference between bond strengths was attributed to each operator's years of clinical experience.