Marginal Integrity of Monolithic Zirconium Oxide Crowns with Two Marginal Designs: (An In-Vitro Study)

Aim: The aim of this study was to assess the marginal integrity of monolithic zirconium oxide crowns with two marginal designs (chamfer and edgeless).Materials and methods: Two maxillary right second premolar typodont teeth were prepared with 2 finish line designs (Chamfer and Edgeless) to receive 22 monolithic zirconia crowns. The crowns were divided into 2 groups according to the design of the finish line (n=11). Preparations were directly scanned, crowns were designed using Exocad software, milled using a five-axis milling machine and checked for seating under magnification. Stereomicroscope and image analysis software were used to measure the vertical marginal gaps (VMG) and marginal chippings. Calculations for the mean VMG and the chipping factor (CF) of each crown were tabulated for statistical analysis.Results: The crowns of chamfer group were associated with VMG mean value (12.85 ± 2.42 μm), while, those of edgeless group recorded (11.42 ± 0.73 μm). Independent t- test revealed no statistically significant difference between the two groups. Regarding CF measurement, chamfer group recorded mean value (0.21 ± 0.62), while the edgeless group recorded (2.92 ± 2.57). Mann-Whitney U test was performed and revealed a statistically significant difference with value (p=0.001) between chamfer group and edgeless group. Conclusions: Monolithic zirconia with chamfer and edgeless finish line preparation designs proved to have superior marginal accuracy. Edgeless margin had higher chipping tendency in comparison to chamfer margin. Five axis milling strategy proved to be a reliable construction protocol for edgeless zirconia crown margins.