Objective To compare the retention of selected cores to all- ceramic posts in post- and- core system, in which the ceramic core was combined with the post by direct sintering, adhering, and the composite resin core was formed onto the post. Methods A total of 15 all- ceramic post fabricated by alumina- zirconia nano- composite infiltrated ceramics were divided into three groups. In group A, forming and combining the ceramic core with the post by direct sintering. In group B, combining the ceramic core with the post by adhering. In group C, forming composite resin core onto the post. Each specimen was placed into a special jig along the post axis and subjected to a load on INSTRON 4302 universal testing instrument until failure. Results There was a statistically significant difference between the groups（P0.05）. Conclusion A reliable retention of the core to the post can be achieved when the alumina- zirconia nanocomposite infiltrated ceramic core is formed and combined with the post by direct sintering, which offers significantly higher retention than adhering and forming composite resin core onto the post.
