Purpose: This study evaluated the marginal gap of crowns fabricated using two new chairside computer-aided design/computer-aided manufacturing systems on preparations completed by clinicians with varying levels of expertise to identify whether common preparation errors affect marginal fit.The null hypothesis is that there is no difference in the mean marginal gaps of restorations of varying qualities and no difference in the mean marginal gap size between restorations fabricated using the PlanScan (D4D, Richardson, TX, USA) and the CEREC Omnicam (Sirona, Bensheim, Germany).
Material and Methods: The fit of 80 lithium disilicate crowns fabricated with the E4D PlanScan or CEREC Omnicam systems on preparations of varying quality were examined for marginal fit by using the replica technique.These same preparations were then visually examined against common criteria for anterior all-ceramic restorations and placed in one of four categories: excellent, good, fair, and poor. Linear mixed modeling was used to evaluate associations between marginal gap, tooth preparation rating, and fabrication machine.
Results: The fit was not significantly different between both systems across all qualities of preparation.The average fit was 104 microns for poor-quality preparations, 87.6  for fair preparations, 67.2  for good preparations, and 36.6  for excellent preparations.
Conclusion: The null hypothesis is rejected. It can be concluded that preparation quality has a significant impact on marginal gap regardless of which system is used. However, no significant difference was found when comparing the systems to each other.

W. Renne, B. Wolf et al,Evaluation of the Marginal Fit of CAD/CAM Crowns Fabricated Using Two Different Chairside CAD/CAM Systems on Preparations of Varying Quality J Esthet Restor Dent 27:194–202, 2015