Objectives: To compare the marginal gap and internal fit of two milling systems with different milled internal gaps.
Method: A standardised crown preparation was digitised to calculate the preparation surface area and to create 20 stereolithographic replicas. 10 crowns were milled in the CEREC system and 10 in the E4D system. In each, 5 were milled with a luting space of 100μm and 5 with 200μm. The crowns where seated onto their relevant replica, un-cemented, and the marginal gap measured at 20 points around the circumference using a reflex microscope yielding a 2-dimensional vertical gap and a 3-dimensional measurement which included any horizontal gap. The crown and replica combinations were weighed before and after being luted with a light-bodied polyvinyl siloxane (PVS) and with Rely-X luting cement. The internal fit was measured using the formula: internal fit = weight/(surface area x density).
Results: When comparing the internal fit of the two systems no significant difference was found (P>0.05). For the marginal gap a significant difference (p<0.05) was found in: (a) Un-cemented: 2D @ 200μm luting space; 3D @100μm; (b) Silicone Cementation: 2D @ 200μm and 100μm; (c) Rely-X cementation: 2D @100μm.
Conclusion: The internal fit closely followed the milled space but there was variation in the marginal gaps for the two systems; which had few and inconsistent statistically significant differences. Of concern was the increased 3-D gap in both systems over the 2-D gap, which is an expression of greater horizontal discrepancies between the milled crowns and the replica. For the cemented CEREC crowns, this difference was statistically significant @ 200μm luting space but not @ 100μm. For the E4D, the difference was statistically significant with both the 200μm and 100μm spaces.