Analysis of the marginal gap and internal fit accuracy of 3D printed zirconia crowns using the triple scan protocol.

Abstract

Statement of problem: Zirconia restorations must achieve micrometer-level accuracy in both marginal and internal fit to ensure an adequate fit with the abutments and to reduce the likelihood of clinical failure. Limited research exists on the fit accuracy of 3-dimensionally (3D) printed zirconia crowns, hindering the confirmation of additive manufacturing's effectiveness in producing zirconia restorations.

Purpose: The purpose of this in vitro study was to analyze the marginal gap and internal fit of zirconia crowns fabricated through 3D printing compared with those manufactured by traditional milling.

Material and methods: A mandibular typodont tooth was prepared to receive a monolithic zirconia crown, and 24 epoxy resin replicas were obtained and scanned with a dental laboratory scanner. Using a computer-aided design (CAD) software program (Dental CAD 3.0; evoked GmbH), 24 identical zirconia crowns were designed and sent for additive (LithaCon 210 3y; Lithoz GmbH) and subtractive (Nacera Zirconia; Dental Direkt) manufacturing. The triple scan protocol was used to evaluate the marginal gap and internal fit of all zirconia specimens. All scans were obtained using a laboratory optical scanner (Medit T710; Medit Corp). The resulting STL files of each specimen were superimposed and analyzed using a 3D analysis software program (Medit Design v.2.1.4; Medit Corp). Heat maps were generated to represent all deviations. An independent (nonpaired) t test was performed to compare the fit of crowns fabricated with both techniques (α=.05).

Results: The 3D printed zirconia crowns exhibited a significantly higher marginal gap (87.7 ±7.4 µm) compared with the milled crowns (57.5 ±7.0 µm) (P<.05). Similarly, the internal gap was greater in the 3D printed group (107.4 ±4.9 µm) than in the milled group (86.6 ±7.6 µm) (P<.05).

Conclusions: While 3D printed zirconia crowns demonstrated higher marginal and internal gap values compared with the milled crowns, both types were within clinically acceptable limits.