Effect of bur grit size on the marginal adaptation of glass ceramic restorations

Purpose This in vitro study aimed to investigate the effect of different grit sizes of dental burs on the marginal adaptation of lithium-reinforced glass-ceramic restorations. The objective was to determine if finishing with fine-grit burs after initial preparation with coarser-grit burs enhances the marginal adaptation of restorations produced using computer-aided design and computer-aided manufacturing (CAD-CAM) technology. Materials and methods Fifty impacted human molar teeth with intact enamel were extracted and divided into five groups (n = 10 per group). For group 1, a neutral band chamfer bur (107 mu m) was used, while for group 2, a black band bur (181 mu m) was used. A green band bur (151 mu m) was used for group 3. For group 4, preparation was done using a black band bur and finished with the red band bur (46 mu m), while for group 5, a green band bur was used for preparation and finished with the red band bur. Three-dimensional (3D) scans of the prepared teeth were obtained using an intraoral scanner (Virtuo Vivo, Dental Wings), and CAD software was used to design the crowns. The restorations were milled from lithium disilicate blocks (IPS e.max CAD, Ivoclar Vivadent) on a chairside milling machine (M10, Camcube). Marginal gap assessment on the buccal, mesial, palatal/lingual, and distal surfaces by a stereomicroscope at 20x magnification and with 840 LP/mm resolution was performed. The measurements were performed for 32 equidistant points per sample, totaling 1600 points. ImageJ software was used for the analysis. Additionally, scanning electron microscopy (SEM) was used on 10 samples for validation. Statistical analysis was conducted using the Kruskal-Wallis and Mann-Whitney U tests at the 0.05 significance level. Results There was a statistically significant difference in marginal adaptation between the different groups, with groups 4 (Black-Red) and 5 (Green-Red) showing a better marginal fit (p < 0.05). Within each group, no significant difference was observed between the buccal, mesial, distal, and palatal sides. Conclusion Finishing tooth preparation with a fine-grit red diamond bur after using coarser-grit burs significantly enhances the marginal adaptation of glass-ceramic restorations produced by CAD-CAM technology. This technique could lead to better clinical outcomes in patients treated with such restorations.