Marginal Adaptation of Different Monolithic Zirconia Crowns with Horizontal and Vertical Finishing Lines: A Comparative in Vitro Study

Abstract

Background: A tooth preparation design determines marginal accuracy, which is crucial to the durability of all-ceramic restorations. Objective: An evaluation of marginal adaptation to different tooth preparation techniques and zirconia materials was conducted in this study. Materials and Methods: Based on the preparation design, 48 human maxillary first premolars in good health were divided into two main groups. Group A (chamfer) and Group B (vertical). Within each main group were three subgroups, comprising eight teeth each, distinguished by the type of zirconia material employed (Zircad LT, MT, and Prime by Ivoclar Vivadent). All samples were prepared by the same operator using a dental surveyor. Intra-oral scanning was performed on the prepared teeth. SironaInLab CAD 20.0 software was used to design crowns, which were subsequently generated using a 5-axis milling machine. Crowns were bonded to their corresponding teeth using self-adhesive resin cement. Marginal gap measurements were taken in micrometers ( m) before and after cementation at sixteen sites per sample using a digital microscope at 230x magnification. The collected data were evaluated using statistical analysis using the independent t-test, paired t-test, and ANOVA, with a 0.05 significance level. Results: The vertical preparation group exhibited the smallest marginal gap, while the chamfer group displayed the largest. This disparity was statistically significant across all materials for both pre-and post-cementation measures. The differences between monolithic zirconia crowns were not statistically significant. Conclusion: The vertical preparation design illustrated significantly better marginal adaptation than the chamfer preparation design; materials comparisons showed a comparable marginal gap. The mean value of the marginal gap after cementation significantly increased in all groups.