The Effect of Diamond Bur Wear During Grinding on the Marginal Gap of Zirconia Lithium Silicate Single Crowns: An In Vitro SEM Analysis

Objectives: In this in vitro study, we aimed to evaluate the effect of bur wear during grinding on the marginal gap of Zirconia Lithium Silicate (ZLS) single crowns. Methods: A single maxillary right canine typodont tooth, pre-prepared for a full ceramic crown, was scanned using an intra-oral scanner. A total of 32 ZLS crowns were ground using a four-axis grinding unit and divided into four equal groups (n = 8) based on the grinding sequence to represent progressive bur wear: Group 1 (crowns 1–8), Group 2 (crowns 9–16), Group 3 (crowns 17–24), and Group 4 (crowns 25–32). All crowns were ground consecutively using the same set of diamond burs. Each crown was temporarily cemented to the typodont tooth, and the marginal gap was measured at four reference points (buccal, palatal, mesial, distal) using scanning electron microscopy (SEM) at ×250 magnification. A Kolmogorov–Smirnov test performed on the study variables indicated a normal distribution (p > 0.05). Results: One-way ANOVA revealed no significant differences in the mean total marginal gap between the groups (p = 0.117), with values of 47.20 ± 5.16, 44.62 ± 7.23, 54.14 ± 10.02, and 48.53 ± 7.87 μm for Groups 1, 2, 3, and 4, respectively. Furthermore, no significant differences were found regarding a specific surface (distal, mesial, palatal, buccal) (p > 0.05). Conclusions: The cumulative wear of diamond burs after the consecutive grinding of 32 ZLS crowns did not significantly affect the marginal adaptation. All recorded marginal gaps were well within the clinically acceptable range (<120 μm).