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Evaluation of the Vertical Marginal Fit of CAD-CAM Zirconia, Pressable Lithium Disilicate, CAD-CAM Cobalt Chromium and Direct Metal Laser Sintered Cobalt Chromium Copings- An Invitro Comparative Analysis

Introduction: The longevity, durability and success of conventional fixed partial dentures and single crowns have been known to be attributed to the marginal fit of these restorations. Therefore, many studies lay emphasis on accurate marginal fit of the crowns. It has been the focus of various investigations in literature. However, there is limited literature comparing marginal accuracy CAD/CAM zirconia, Pressable Lithium Disilicate, CAD/CAM Cobalt-Chromium and Direct Metal Laser Sintered (DMLS) copings. Aim: Verification and comparative evaluation of the vertical marginal adaptation of CAD/CAM Zirconia, Pressable lithium Disilicate, CAD/CAM Cobalt-Chromium and DMLS copings. Materials and Methods: This invitro study was planned with an aim to evaluate the vertical marginal adaptation of CAD/CAM Zirconia, Pressable Lithium Disilicate, CAD/CAM Cobalt-Chromium and DMLS copings. A custom- made metal master model was prepared simulating the shape and dimension of tooth preparation resembling a first premolar using a Computer Numerically Controlled (CNC) milling machine. An elastomeric impression of the custom-made stainless steel model was made with addition silicone using dual mix/double step technique. All impressions were poured in Type IV dental stone and 60 stone dies were obtained. The samples were divided into four groups and each group had 15 samples (stone dies)- CAD/CAM zirconia (Group A), Pressable Lithium Disilicate (Group B), CAD/CAM Cobalt Chromium (Group C), and Direct Metal Laser Sintered Cobalt Chromium copings (Group D). The marginal fit was analysed at four reference marks on the working die stone model i.e., 0° (Buccal surface), 90° (Mesial Surface), 180° (Lingual surface), and 270° (Distal surface) on the stone die using a stereomicroscope. Comparison between groups was done by using one-way ANOVA test followed by a Post-Hoc Tukey-Kramer multiple comparisons test. Results: The mean marginal gap (in μm) for Group A was 53.185±25.83, respectively. The mean marginal gap (in μm) of Group B was 66.08±22.27, respectively. The mean marginal gap (in μm) of Group C was 108.62±23.93, respectively. The mean marginal gap (in μm) of Group D was 28.54±13.53, respectively. Tukey’s post-hoc analysis showed that the mean difference in the vertical marginal gap in Group C and the other three groups was statistically significant (p<0.05) i.e., marginal discrepancy of group C was more than Group A, Group B and Group D. Conclusion: The marginal fit of DMLS copings is more accurate as compared to CAD/CAM Zirconia, Pressable Lithium Disilicate and CAD/CAM Cobalt-Chromium copings.