Is Additive Manufacturing of Dental Zirconia Comparable to Subtractive Methods When Considering Printing Orientation...

The aim of this systematic review and meta-analysis was to determine whether the production of monolithic dental zirconia using additive manufacturing (AM), with consideration of different printing directions and layer thicknesses, enhances its mechanical and physical properties relative to subtractive manufacturing (SM).

This systematic review followed PRISMA guidelines and was registered on the Open Science Framework. The PICO strategy was used, focusing on monolithic dental zirconia, comparing AM (stereolithography [SLA] and digital light processing [DLP]) with SM (i.e., CIPing/presintering/milling). In vitro studies were included. Electronic searches were conducted across multiple databases and gray literature, followed by data selection and extraction. Methodological quality was assessed using the QUIN tool for in vitro risk of bias. Mean and standard deviation of flexural strength, density, roughness, and specimen count per group were used to calculate the mean difference (MD) with a 95% confidence interval (CI) in the meta-analysis.

A total of 31 studies were included in the qualitative synthesis and 21 in the quantitative analysis. Most were classified as having a medium risk of bias. The meta-analysis indicated that AM zirconia exhibited lower flexural strength than SM zirconia. However, subgroup analyses revealed no significant difference in the flexural strength of samples fabricated using SLA technology or printed at the 0° orientation relative to SM zirconia. Individually, AM zirconia fabricated with 25 or 50 μm layer thicknesses possessed lower flexural strength than SM zirconia, regardless of print direction. No differences were observed between the manufacturing methods regarding surface roughness, although SM demonstrated significantly higher density than AM zirconia.

AM dental zirconia demonstrated lower flexural strength when pooled across printing technologies, build orientations, and layer thicknesses. However, it exhibited comparable strength to SM zirconia at 0° or fabricated using SLA technology. Both AM and SM methods yielded similar surface roughness, with SM producing higher density. Most studies had a medium risk of bias, suggesting the need for further research and methodological rigor, particularly regarding translucency.

Based on current in vitro evidence, AM zirconia may show potential for posterior crowns; however, further clinical validation is needed, especially for the anterior region due to insufficient translucency to meet esthetic demands.