Accuracy of 3-dimensional printing of dental casts: A proposal for quality standardization
The Journal of Prosthetic Dentistry
Statement of problem
A digital workflow in fixed prosthodontics may use a 3D printer to obtain a cast for porcelain application. Standards exist that define the accuracy of traditional casts, but the accuracy requirements of 3D-printed casts have not been defined.
Purpose
The purpose of this retrospective study was to investigate how the accuracy of 3D-printed casts affected prosthesis fit and whether they correctly reproduced interproximal contacts.
Material and methods
Copings with different die spacings were used to test different 3D-printed casts of the same dental arch. The accuracy of the 3D casts was assessed by imaging and comparing the resulting standard tessellation language (STL) files with the original through a matching software program. Accuracy scores were then correlated with a score measuring how well the copings fit the casts. The first data set was obtained from a patient receiving restoration of the 4 maxillary incisors. The teeth were prepared, the dental arch was imaged intraorally, and 10 resin casts were printed with four 3D printers. Two sets of 4 zirconia test copings were prepared, and 3 clinicians assessed their fit on each cast. A further set of casts was created from a second patient requiring prosthetic restoration for 5 adjacent teeth to assess whether undersizing affected the best fit of the copings on their dies.
Results
The clinical scores and accuracy scores did not correlate. The results suggested that printed dies showing a certain degree of undersizing might provide a better fit than those showing better correspondence to the actual anatomic structure. The oversized dies were the worst. Only 7 of 17 casts being assessed were deemed suitable for veneering of the copings. The undersized casts tested clinically better than casts printed by using the same printer under standard settings.
Conclusions
This retrospective study indicated that 3D-printed casts that do not allow copings to fit appropriately usually show mean excess oversizing. Axially undersizing the printed dies on casts might allow a better fit of copings to be veneered.
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