Modifying Digital Occlusal Spacer Effect on the Marginal Gap of Zirconia-Reinforced Lithium Silicate Crowns: In Vitro Scanning Electron Microscopy Evaluation.

PURPOSE: To evaluate the effect of modifying digital occlusal spacers on the marginal gap of full monolithic zirconia-reinforced lithium silicate (ZLS) crowns using a 4-axis machine. MATERIALS AND METHODS: In total, 45 acrylic teeth with preparation for full crowns were divided into three groups with different occlusal digital spacers (60, 90, and 120 μm). All 45 abutments were scanned by an intraoral scanner (IOS), and a 4-axis machine grinded ZLS crowns. Each crown was cemented to the abutment using universal resin cement, and for each unit (crown and abutment) a scanning electronic microscope (SEM) was used to assess the marginal gap. For comparing the marginal gap between the three groups, Kolmogorov-Smirnov test was performed on the study variables and indicated a normal distribution (P > .05) followed by one-way ANOVA with post-hoc Bonferroni test (α = .05). RESULTS: The total mean marginal gap (TMMG) for the 120-µm (101.38 ± 17.94 µm) occlusal spacer was found to be significantly higher compared to the 90-µm (72.84 ± 27.21 µm) and 60-µm (60.16 ± 29.34 µm; P < .05) occlusal spacers. There was no significant difference between the 90-μm (72.84 ± 27.21 µm) and 60-μm (60.16 ± 29.34 µm) groups (P = .533). CONCLUSIONS: A clinically acceptable marginal gap (< 120 µm) was obtained for all three occlusal spacers (60, 90, 120 µm), and as the digital occlusal spacer was reduced the marginal gap reduced as well. The 120-µm occlusal spacer showed a significantly higher marginal gap compared to 90 and 60 µm. The digital occlusal spacer that should be favorable for ZLS crowns is 60 µm.