Influence of milling systems and marginal configurations on the fit of yttrium stabilized tetragonal zirconia polycrystals (Y-TZP)' copings

Reliability of automatic finish line detection for tooth preparation in dental computer-aided software

PURPOSE

This study aimed to investigate the accuracy of automatic tooth finish line registration compared to manual registration with regard to various finish line configurations and dental computer-aided design (CAD) software.

METHODS

Finish line registrations were performed on 15 digital tooth models with different finish line configurations (edge roundness radius = 0 mm, 0.2 mm, and 0.4 mm; edge angle = 30°, 60°, 90°, 120°, and 150°) using automatic and manual methods for designing virtual copings (N = 150). The discrepancies between the registered finish line extracted from the copings and the actual finish line segmented from the digitized tooth model were measured. Three-way analysis of variance (ANOVA) and post-hoc analyses with Bonferroni correction (α = 0.05) were used to analyze the results.

RESULTS

The finish line configurations, registration methods, and CAD software interacted with the accuracy of the registered finish line (p = 0.001). The automatic finish line registration method exhibited larger error values than the manual method, especially at high finish line edge roundness and obtuse edge angles for both EXOCAD and R2CAD software (p < 0.001). The difference in dental CAD software affected the registration accuracy in the automatic method (p < 0.001), but not in the manual method (p = 0.676).

CONCLUSIONS

Finish line registration errors may occur when the automatic registration method is applied to the indistinct edge of tooth preparation. The accuracy of the automatic finish line registration could differ according to the CAD software program.

Marginal Misfit of 3D-Printed (Selective Laser Sintered), CAD-CAM and Lost Wax Technique Cobalt Chromium Copings with Shoulder and Chamfer Finish Lines: An In-Vitro Study

Background and Objectives: The aim was to compare the Misfit of 3D-Printed, Selective laser melting (SLM), milled (Computer aided design-Computer aided manufacture CAD-CAM) and Lost wax technique (LWT) fabricated Cobalt chromium (CoCr) alloy copings on shoulder (SH), radial shoulder (R-SH) and chamfer (CH) finish line configuration. Materials and Methods: Ninety resin, second maxillary premolar teeth were prepared for metal-ceramic crowns, equally divided into (n = 30) SH, R-SH and CH margin preparations. For each preparation design (SH, R-SH and CH), CoCr copings were prepared using SLM, CAD-CAM and LWT. This resulted in nine study groups with 10 CoCr copings each. The marginal misfit of specimens was assessed with a high-resolution digital microscope. Misfit was evaluated in vertical and horizontal dimensions in μm. Data were analyzed using ANOVA and a post hoc multiple comparisons test. Results: For vertical misfit, the highest was observed in SLM samples with chamfer margin (167.96 ± 24.1), and the least was shown by CAD-CAM samples with radial shoulder (58.8 ± 12.53). CAD-CAM and shoulder margins showed the least vertical misfit. For horizontal misfit, the maximum was observed in SLM samples with shoulder margin (137.94 ± 37.85) and the least by LWT samples with chamfer (89.38 ± 14.81). Chamfer margins and LWT samples showed the least horizontal misfit among the group samples. Fabrication technique and finish line design play a critical role in reducing the marginal misfit of CoCr copings. Conclusions: For vertical misfit, SLM copings showed poor outcomes compared to CAD-CAM specimens, however comparable outcomes to Cast specimens. SLM copings showed comparable horizontal misfit outcomes to CAD-CAM specimens and low misfit compared to Cast copings, respectively. Vertical misfit was low with shoulder margins, and horizontal misfit was better with chamfer marginal configuration.

Marginal and Internal Precision of Zirconia Four-Unit Fixed Partial Denture Frameworks Produced Using Four Milling Systems

Background: CAD/CAM systems enable the production of fixed partial dentures with small and reproducible internal and marginal gaps. Purpose: The purpose of this study was to evaluate the reproducibility of the marginal and internal adaptations of four-unit fixed partial denture frameworks produced using four CAD/CAM systems. Materials and Methods: Prepared dies of a master model that simulated the loss of the first left molar were measured. Fifteen frameworks were manufactured using four CAD/CAM systems (A–D). The internal fit was determined by the replica technique, and the marginal gap was determined by microscopy. ANOVA was carried out to detect significant differences, and the Bonferroni adjustment was performed. The global level of significance was set at 5%. Results: The mean gap size ranged from 84 to 132 µm (SD 43–71 µm). The CAD/CAM systems showed significant variance (p < 0.001), and system A (VHF) showed the smallest gaps. The smallest gaps for each system were in the molar part and in the marginal region of the frameworks (p < 0.001). Conclusions: The CAD/CAM systems showed significantly different gap sizes, particularly between premolars and molars and among the marginal, axial and occlusal regions. All of the systems are suitable for clinical application.