Under quasi-clinical conditions, Dicor, Hi-Ceram, Ceraplatin and PFM (porcelain butt margin) crowns with ceramic shoulders manufactured by commercial laboratories for the same metal master die were examined for marginal defects under the electron microscope. With equal cementing conditions and points of measurement for all crowns, the PFM crowns were found to be significantly superior to the other crown types. However, this result becomes relativistic in view of the great statistical variances involved.