Purpose: This study was to compare adaptations of lithium disilicate CAD/CAM crowns fabricated with different scanning systems. Methods: This study selected the mandibular right first molar as an abutment for experiments and produced 10 working models. Lithium disilicate crowns appropriate for each abutment were produced by using a CEREC$^{(R)}$ CAD/CAM system. The independent t-test was then used to compare and analyze the data obtained from the two groups(${alpha}$=0.05). Results: Mean(SD) adaptation were $86.93(22.82){mu}m$ for the InS group, $88.42(26.77){mu}m$ for the ExS group. They were no statistically significant differences between groups for adaptation(p>0.05). Conclusion: Within the limitations of this study, the results suggest that the accuracy of all investigated optical scanner were satisfactory for clinical use. Further assessment and improvement of the lithium disilicate ceramic for the fabrication of FPDs is evidently still required.