Comparison of the Marginal Adaptation of Zirconium Dioxide Crowns in Preparations with Two Different Finish Lines

Purpose: The purpose of this study was to evaluate the marginal adaptation of zirconium dioxide crowns in preparations with two different finish line configurations before and after porcelain firing cycles, after a glaze cycle, and after cementation. Materials and Methods: Twenty human molar teeth were prepared to receive full crowns; ten were prepared with a 90 degrees round shoulder and another ten with a 45 degrees chamfer finish line. Zirconium dioxide copings were fabricated using CAD/CAM technology (Lava (TM) system). They were then veneered with a low-fusing glass-ceramic (IPS e.max (R) Ceram). Finally, they were glazed and cemented with a resin-composite cement (RelyX (TM) Unicem, Aplicap (TM)). Measurements for marginal adaptation using stereomicroscopy (40 x) were performed at four stages: copings (S1), after porcelain firing cycles (S2), after glazing (S3), and after cementation (S4). One-way ANOVA was used to assess the influence of the finish line design on the marginal adaptation in each stage. Two-way ANOVA with repeated measurements was performed to assess the influence on the marginal adaptation of the porcelain firing cycles, glaze firing cycle, and cementation. Results: The measured marginal gap mean values for the shoulder group (mu m) were: 50.13 (S1), 54.32 (S2), 55.12 (S3), and 59.83 (S4). The values for the chamfer group were: 63.56 (S1), 71.85 (S2), 74.12 (S3), and 76.97 (S4). When comparing marginal gaps between specimens with two different finish lines, differences were noticed at the four studied stages (p= 0.0165, p= 0.0027, p= 0.0009, and p= 0.0009, respectively). No differences were manifested in the marginal gap measurements of the shoulder group at the different stages of fabrication (p= 0.4335); however, in the chamfer group, differences were noticed between S1 and S3 (p= 0.0042). Conclusions: Marginal adaptation was influenced by the finish line design. The firing cycles significantly affected the chamfer group; nevertheless, the marginal gap was within the range of clinical acceptability.