Comparison of Marginal Fit and Fracture Strength of a CAD/CAM Zirconia Crown with Two Preparation Designs

The purpose of this in vitro study was to compare the marginal adaptation and fracture resistance of a zirconia-based all-ceramic restoration with two preparation designs.
Twenty-four mandibular premolars were randomly divided into two groups (n=12); the conventional group received a peripheral shoulder preparation and the modified group received a buccal shoulder and proximal/lingual chamfer preparation. The marginal fit of the zirconia crowns (Cercon) was evaluated using a stereomicroscope. After cementation, load was applied to the crowns. The mean fracture load and the mean marginal gap for each group were analyzed using t-test (P=0.05).
The mean marginal gap was 71±16µm in the conventional group and 80±10µm in the modified group, with no significant difference (P=0.161). The mean fracture strength was 830±153N for the conventional group and 775±125N for the modified group, with no significant difference (P=0.396). All but one fracture occurred in the veneering ceramic.
Less aggressive preparation of proximal and lingual finish lines for the preservation of tooth structure in all-ceramic restorations does not adversely affect the marginal adaptation or fracture strength of the final restoration.