Predicting marginal fit of CAD/CAM crowns based on the presence or absence of common preparation errors

Confusion exists as to what constitutes an ideal ceramic crown preparation and whether certain deviations from the ideal can affect the marginal fit of the milled restoration.

This study evaluated the marginal gap of E4D crowns fabricated on preparations completed by clinicians with varying levels of expertise to identify whether common errors affect marginal fit.

The fit of 75 crowns fabricated with the E4D system on preparations of varying quality were examined for marginal fit by using the replica technique. These same preparations were then visually examined for common criteria for ceramic restorations and placed in one of 3 categories: excellent, fair, or poor. These visual examinations sought the presence of common preparation errors, particularly those involving the finish line. The average marginal gap values and standard deviations were calculated for each category, and the Kruskal-Wallis test was used to determine significance.

The results showed a statistically significant correlation between the marginal fit of a CAD/CAM fabricated crown and the quality of the preparation. The mean marginal gap of the crowns fabricated on ideal preparations was 38.5 µm, those considered fair had a mean marginal gap of 58.3 µm, while those categorized as poor averaged 90.1 µm. The fit differences among all 3 groups were statistically significant (P<.05).

Within the limitations of this in vitro study, it can be concluded that preparation quality has a significant impact on marginal gap on crowns fabricated with a CAD/CAM system.