Purpose: Evaluation of marginal and internal fit of monolithic zircon crown restoration fabricated by scanning three different die material ;3D printed resin versus stone and epoxy resin dies.
Materials and methods: A standardized Computer Numerical Control machine (CNC) will be used to fabricate a stainless steel master die simulating a prepared tooth with an occluso-gingival height of 6 mm, a taper of 6° and 1 mm shoulder circumferentially. The overall diameter of the die at the base is 8.5 mm Three groups of zircon crown (Prettau® Zirconia manufactured by Zirkonzahn® and E-Denstone®). 10 crowns per each group fabricated digitally from three different dies as follow: 1) First group (G1) 3D printed resin die (light cured methacrylate (Envision TEC). 2) Second group (GII), Epoxy resin die. 3) Third group (GIII) Type IV stone die (Zhermach spa, Bouazecchino ST, Badia polesine, Italy). Each crown fabricated from its specific die seated and stabilized on the master stainless steel die. Demark certain points on the crown margin and photographed using USB Digital microscope with a built-in camera (Scope Capture Digital Microscope, Guangdong, China) connected with an IBM compatible personal computer using a fixed magnification of 45X. Internal discrepancy of the copings was measured by a replica technique. Each coping was filled with light-body silicone (zetaplus, zhermack, italy), the replicas (heavy and light –body silicon) were carefully removed from the crown and sectioned mesio-distally into two equal segments with three regions measured on each section (margin, axial and occlusal), yielding 8 internal measurements for each coping. A digital image analysis system (Image J 1.43U, National Institute of Health, USA) was used to measure and qualitatively evaluate the gap width.
Results: Data analysis was performed in several steps. Initially, descriptive statistics for each group results. One-way ANOVA followed by pair-wise Tukey's post-hoc tests were performed to detect significance between all groups. The absolute marginal gap mean ±SD values recorded for first group were (18.0305±6.99717), for II group were (41.0989± 21.55940) and for III group were (18.2960 ± 7.177245). It was found that the highest absolute marginal gap mean value recorded for IIgroup followed by III group mean value.While the lowest absolute marginal gap mean value recorded for I group. The difference between all die groups was statistically significant as revealed with one-way ANOVA test (p=0.01). Pair-wise Tukey's post-hoc test showed non-significant differences while (p=0.99) between (groups III,I), While between (groups II, III) and (groups II, I) there is significant differences where (p=0.01). Descriptive statistics, showing mean values and standard deviations (SD) for internal fit measured in µm recorded for all die groups are summarized as following: One way ANOVA showed that there is a significance between the three groups p ≤ 0.05 and also Pair-wise Tukey's post-hoc test showed non-significant differences (p=0.926) between group I and III, While the difference between group I and II was significant P=0.001 and groupII and III was significant where p=0.001.
Conclusion: With the limitation of this study, it was found that: 3D printed resin die provide a restoration with good marginal and internal fit . All the die materials provided crown restorations with acceptable fit.