Factors affecting flexural strength of 3D-printed resins: A systematic review

The strength of 3D-printed resins is affected by different factors, but review articles clarifying these factors are limited. This review lists the factors affecting the strength of 3D-printed resins and the possible correlations between them to answer the study question: What are the factors affecting the flexural strength of 3D-printed resins?

A database search (PubMed, Google Scholar, and Scopus) was performed, limited to English-language publications between 2010 and February 1, 2022. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were used for study selection. The modified Consolidated Standards of Reporting Trials (CONSORT) checklist was used to determine the risk of bias of the included studies in this review. The data analysis was descriptive due to the presence of many variables in the included studies.

Out of 123 studies, 26 were reviewed for full-text analysis, and 19 met the inclusion criteria and were thus included in this systematic review. The included studies were divided according to the investigated resin: 5 studies tested provisional restorations, seven tested denture base resins, 2 tested occlusal devices, 3 tested orthodontic appliances, 1 tested denture teeth, and 1 tested surgical guide resins. These studies investigated the flexural strength of 3D-printed resins, with different factors, such as reinforcement with fillers or nanofillers; printing orientation, angulation, and directions; post-polymerization time and temperature; third-party printing (switching between printers and materials); printing layer thickness; and post-printing rinsing time. Most factors significantly affected the flexural strength of 3D-printed resin.

The strength of 3D-printed resins could be improved with one or more of the following factors: filler or nanofiller addition; printing orientation, angulation, or directions; printing layer thickness; and post-polymerization time and temperature. However, further studies combining these factors are recommended.