In vitro fitting accuracy of copy-milled alumina cores and all-ceramic crowns

The purpose of this study was to evaluate the marginal and internal fit of alumina cores and all-ceramic crowns in a new preparation design for abutment teeth devised for copy milling.

Using conventional dies and dies from the new type of preparation design, 20 alumina cores were produced by copy milling, 10 cores in each die type. Also using the new type of die, another 10 final crowns were fabricated. Each of the 30 specimens was returned to its original die and embedded in epoxy resin. Each specimen was then sectioned labiolingually and measured for gaps at the margin, in the central area, and at the incisal edge.

The alumina cores fabricated using the new type of die had mean gaps of 30 to 40 microns at the margins of the labial and lingual sides, which was significantly smaller than the gaps (67 to 130 microns) found in the alumina cores produced with the conventional type of die. The final crowns had mean gaps of 44 to 63 microns at the margins and on the inner surfaces. There was no significant difference in the gaps between the alumina cores produced using the new type of die and those found in the final crowns.

The new type of die was effective in allowing the fabrication of all-ceramic crowns that provide excellent marginal and internal fit by copy milling.