The aim of this study is to investigate the internal morphology of all-ceramic prostheses before seating. Micro X-ray CT was used to inspect three dimensionally the locations and sizes of pores within experimentally fabricated all-ceramic crowns as well as measure the veneer and core thickness. Scanning electron microscopy (SEM) was used to examine the fracture sites of clinically failed prostheses. Micro X-ray CT analysis revealed the distribution patterns of pores within the all-ceramic prostheses, and SEM fractographic analysis indicated a strong relationship between the existence of pores and crack propagation. Therefore, micro X-ray CT is a useful tool for nondestructive inspection of the internal morphology of all-ceramic prostheses to identify the critical defects before seating.