Effect of build orientation on marginal and internal discrepancies of zirconia crowns fabricated by using digital light processing 3D printing: A clinical study.
STATEMENT OF PROBLEM Digital light processing (DLP) 3-dimensional (3D) printing enables the additive fabrication of monolithic zirconia crowns; however, the effect of build orientation on their marginal and internal discrepancies in vivo, relative to conventionally milled zirconia crowns, remains insufficiently characterized. PURPOSE The purpose of this clinical study was to compare the marginal and internal discrepancies of zirconia crowns fabricated by conventional milling and by DLP 3D printing and to evaluate the influence of build orientation (0, 45, and 90 degrees) on the fit of DLP- printed crowns. MATERIAL AND METHODS Ten participants requiring a single posterior zirconia crown in the maxilla or mandible were enrolled. For each participant, 4 crowns with identical designs were fabricated: 1 milled crown (Ceramill Motion 2; Amann Girrbach AG) and 3 DLP-printed crowns (TD 6; 3D Controls Co Ltd) at build orientations of 0, 45, and 90 degrees. 4Y PSZ zirconia blocks (Ceramill Zolid FX; Amann Girrbach AG) and a 3Y TZP zirconia slurry (3DCera; 3D Controls Co Ltd) were used. The silicone replica technique (Fit Checker; GC Corp) was used to measure the absolute marginal discrepancy (AMD), marginal gap (MG), and internal discrepancies at the chamfer, axial, line angle, and occlusal regions. Replica thicknesses were quantified under a digital microscope. Data were analyzed with a 1-way repeated measures analysis of variance, with fabrication condition treated as a within-subject factor. Post hoc pairwise comparisons were adjusted with the Holm procedure, and partial η2 values were calculated to quantify effect size (α=.05). RESULTS Fabrication condition significantly affected AMD, MG, chamfer discrepancy, angle discrepancy, and occlusal discrepancy in the omnibus repeated-measures ANOVA (all P<.05), but not axial wall discrepancy (P=.073). Holm adjusted pairwise comparisons showed significant differences for AMD, angle discrepancy, and occlusal discrepancy (all P<.05), whereas no adjusted pairwise difference remained significant for MG or chamfer discrepancy (P>.05). CONCLUSIONS Zirconia crowns fabricated at 0-degrees build orientation using the TD-6 DLP printer and 3DCera 3Y TZP slurry exhibited marginal and internal discrepancies comparable with those of Ceramill Zolid FX 4Y PSZ conventionally milled crowns, whereas 45- and 90-degree build orientations resulted in inferior adaptation, particularly at the occlusal surface. Build orientation is therefore a critical parameter for DLP printed zirconia crowns using this specific system and should be carefully controlled to achieve acceptable adaptation in clinical practice.