comparison of marginal fit and fracture strength of a cad/cam zirconia crown with two preparation designs

objectives : 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. materials and methods: 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). results: 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. conclusion: 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.