Fit, Precision, and Trueness of 3D-Printed Zirconia Crowns Compared to Milled Counterparts

Abstract

Precise fit of a crown and accurate reproduction of the digital design are paramount for successful treatment outcomes and preservation of clinician and technician time. The study aimed to compare the internal fit, marginal adaptation, precision, and trueness of 3D-printed zirconia crowns compared to their milled counterpart. A total of 20 monolithic 3 mol% yttria stabilized-zirconia crowns (n = 10) were made using computer-assisted design (CAD) followed by additive (3D-printed) and subtractive (milled) manufacturing. Digital scanning of the master die with and without a fit checker followed by image superimposition, and analysis was performed to evaluate internal and marginal adaptation in four areas (occlusal, axial, marginal, and overall). ISO 12836:2015 standard was followed for precision and trueness evaluation. Statistical analysis was achieved using a t-test at α = 0.05. Internal fit and marginal adaptation revealed no significant difference between the two test groups (p > 0.05). The significant difference in trueness (p < 0.05) was found between the two groups in three areas (occlusal, axial, and internal). The best and worst trueness values were seen with 3D-printed crowns at occlusal (8.77 ± 0.89 µm) and Intaglio (23.90 ± 1.60 µm), respectively. The overall precision was statistically better (p < 0.05) in the 3D-printed crowns (9.59 ± 0.75 µm) than the milled (17.31 ± 3.39 µm). 3D-printed and milled zirconia crowns were comparable to each other in terms of internal fit and marginal adaptation. The trueness of the occlusal and axial surfaces of 3D-printed crowns was better, whereas the trueness of fitting surface of milled crowns was better. 3D-printed crowns provided a higher level of precision than milled crowns. Although the internal and marginal fit of both production techniques were comparable, 3D printing of zirconia produced more precise crowns.

Manufacturing and Characterization of Dental Crowns Made of 5-mol% Yttria Stabilized Zirconia by Digital Light Processing

“…Mean RMS values for the internal gap and marginal discrepancy were 22.8 ± 1.6 μm and 44.4 ± 10.8 μm, respectively ( Figure 17 B). These values are comparable to those obtained for zirconia dental crowns manufactured using DLP [ 11 , 12 ]. These findings suggest that our DLP technique can offer reasonably high dimensional accuracy with assistance of tightly controlled processing parameters, including initial dimensions of dental crowns, sequential photopolymerization process, and heat-treatment (debinding and sintering).…”

“…From the viewpoint of resolution and accuracy of 3D printing techniques, digital light processing (DLP) and stereolithography (SLA) have been most extensively investigated for the manufacturing of zirconia dental crowns [ 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 ]. These techniques can selectively photo-cure thin layers of zirconia suspensions, where zirconia particles are uniformly dispersed in photocurable monomers, using high-resolution UV engines according to pre-designed 2D images layer-by-layer [ 3 , 4 ].…”

“…However, this bottom-up approach has a potential risk of interfacial failure between photopolymerized layers, caused during detachment of newly photopolymerized layers from a polymer film attached to the bottom of a vat, and frequent damage of the film. On the other hand, in the SLA process, a recoater can directly spread a ceramic suspension onto a previously photopolymerized layer, thus eliminating issues related to the bottom-up approach [ 9 , 10 , 11 , 14 ]. However, this top-down approach requires a large number of ceramic suspensions to fill a vat and the leveling process to ensure uniform thickness is troublesome.…”

“…In addition, our group recently developed a new type of top-down DLP process by employing specifically designed feeding and recoating systems, where ceramic suspensions can be extruded through a nozzle at a controlled rate and then uniformly spread onto previously photopolymerized layers by a recoater [ 6 ]. A number of recent works have demonstrated that DLP and SLA techniques could offer outstanding dimensional accuracies comparable to CAD/CAM [ 10 , 11 , 12 , 13 , 14 , 15 , 18 ]. However, 3D-printed zirconia objects often suffer from imperfections, including pores within layers and weak interfaces between layers, causing severe reductions in mechanical properties [ 5 , 6 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 ] and optical translucency [ 6 , 22 ].…”

Quality Assessment and Comparison of 3D-Printed and Milled Zirconia Anterior Crowns and Veneers: In Vitro Pilot Study

“…Ongoing research aims to improve sintering methods for 3D-printed zirconia. [26][27][28] Cost and fabrication time were not considered, as this was a pilot study. However, the 3D printing workflow can print multiple prosthodontic units at once, related to the size of the build plate.…”