New post and core systems such as glass fiber posts with composite resin cores, are continuously developed and praised for their esthetics and similar elastic modulus to dentin. In this study, three groups of post and core systems (cast post and core, glass fiber and prefabricated metal posts) are tested for resistance to fracture under a continuous load and cyclic loading under similar oral conditions. Zinc phosphate and Panavia 21 were used as cements of choice because of their long history of reliability and dependability. Marginal gap measurements were acquired using a high powered microscope before and after testing in the cyclic loading groups. For the load to failure groups, a constant but slow speed load was applied to the teeth till failure. The two hypotheses for this study were: the glass fiber group would have less marginal gap opening on the lingual after cyclic loading than the other groups. The second hypothesis was the cast post and core would have a higher load to failure than the other groups in this study.