Microstructural impact of additive and subtractive manufacturing on the flexural strength of zirconia: A scoping review.

Abstract

Additive manufacturing (AM) and subtractive manufacturing (SM) are common techniques used for the fabrication of zirconia dental prostheses. However, variability in zirconia composition, AM technologies, and processing parameters has led to heterogeneous microstructural and mechanical results. This scoping review aims to map and critically describe the available in vitro experimental evidence on how composition, manufacturing route (AM or SM), and processing variables influence the microstructural characteristics and flexural strength of zirconia. The review followed PRISMA-ScR guidelines and was registered on the Open Science Framework. A comprehensive search was conducted in PubMed, Embase, Web of Science, ScienceDirect, ProQuest, and Google Scholar, with no time restrictions. Two independent reviewers performed study selection in a blinded manner using predefined eligibility criteria, which included exclusively in vitro experimental studies. Of the 145 articles identified, only eight met the inclusion criteria. The included in vitro studies showed substantial heterogeneity in zirconia compositions, AM technologies, thermal processing protocols, and mechanical testing conditions. SM was generally associated with lower porosity and higher flexural strength values, whereas overlapping ranges of flexural strength and microstructural features were observed in some AM systems depending on composition and processing parameters. Current evidence remains limited and heterogeneous, precluding consistent comparisons between AM and SM zirconia, as well as generalized conclusions regarding their relative performance. These findings highlight the need for standardized experimental protocols and composition-specific analyses in future studies.