Marginal and internal fit of Cerec 3 CAD/CAM all-ceramic crowns.

Purpose: The purpose of this study was to examine the effects of the occlusal convergence angle of the abutment and the computer's luting space setting on the marginal and internal fit of Cerec 3 computer-aided design/manufacturing (CAD/CAM) all-ceramic crowns.
Materials and Methods: Mandibular second premolar all-ceramic crowns were fabricated for nine different conditions using Cerec 3: all combinations of abutments with three different total occlusal convergence angles (4, 8, and 12 degrees) with three different luting space settings (10, 30, and 50 microm). The completed crowns were seated on the abutments, and the marginal gaps were measured. The internal gaps between the crowns and abutments were also measured, using test-fit silicone paste.
Results: When the luting space was set to 10 microm, the marginal gaps of the crowns were greater than when it was set to 30 or 50 microm. When the luting space was set to 30 or 50 microm, the marginal gaps ranged from 53 to 67 microm and were not affected by the occlusal convergence angle of the abutment. The internal gaps were within a range of 116 to 162 microm and tended to decrease as the occlusal convergence angle of the abutment decreased.
Conclusion: When the luting space was set to 30 microm, crowns with a good fit could be fabricated on the Cerec 3 system, regardless of the occlusal convergence angle of the abutment.