Impact of Cut-out-rescan and Data Exchange by Over-scanning Techniques on Marginal Fit of CAD/CAM Lithium Disilicate Crowns.

ABSTRACT

OBJECTIVE: Evaluate the impact of adjustment procedures - cut-out-rescan (COR) and data exchange by over-scanning (DEOS) techniques - through CAD/CAM software on the marginal fit outcome of ceramic crowns. METHODS AND MATERIALS Twenty-eight de-identified teeth were adapted in a mandibular typodont set. Tooth #19 was prepared for a lithium disilicate crown and seven groups, G0 to G6 (n=10), were created based on the rescanned areas (mesial and/or buccal) on the typodont using an intraoral scanner through COR or DEOS techniques. A digital workflow was used to design and mill 70 crowns according to the groups. Each crown was temporarily cemented on tooth #19 and scanned with micro-computed tomography to measure the marginal fit. The data were analyzed statistically by the Kruskal-Wallis test followed by the Mann-Whitney test to compare the groups pairwise as a post-hoc (α=0.05). RESULTS: Statistically significant differences were found for vertical misfit (µm) between the groups for Marginal Gap Buccal (MGB) and Marginal Gap Mesial (MGM) (p=0.003 and p=0.029, respectively). No significant difference was found for Finish Line Buccal (FLB) and Finish Line Mesial (FLM) (p=0.062 and p=0.092, respectively). G3 (COR buccal and mesial) had the highest MGB (57.75 µm), statistically different from all other groups. G4 (DEOS buccal) (41.60 µm) was different from G6 (DEOS buccal and mesial) (44.21 µm) (p=0.023). For MGM, G0 (control) (53.96 µm) was different from G5 (DEOS mesial) (45.76 µm) and G6 (DEOS buccal and mesial) (48.56 vm) (p=0.013 and p=0.041, respectively) and G2 (COR mesial) (58.43 µm) was different from G5 (DEOS mesial) (45.76 µm) (p=0.016). CONCLUSIONS: Despite a statistically significant difference in certain groups for both techniques, COR and DEOS techniques are viable options for image editing during acquisition. Lithium disilicate crowns can be produced with satisfactory marginal gap values utilizing a chairside CAD/CAM system.