Three-dimensional (3D) digitizing and computerization of dental casts is a trend in dentistry especially for orthodontics to substitute stone casts. Generally used laser scanners have a blind side in the measurement of undercuts. As alternative equipment that can digitize regardless of the undercut, the potential of recent multi-slice medical CT was examined. In 3D shape reconstruction, the CT window level affects the size of the object. It was examined, and a CT window level of 800 was found to be suitable. However, the size became slightly smaller than the real object. Then, a correction ratio of 1.002, 1.015 and 1.013 on the X-, Y- and Z-axis was given, and error within 0.08% was accomplished. The measurement and 3D imaging of dental casts was completed within 10 min. The reproducibility of the complicated morphology of dental casts was slightly inferior to that of the latest laser scanners, but the accuracy and operationality regardless of the undercut is noteworthy for clinical application.