Dental zirconia residuals recycling: processes, applications, and future perspectives: a scoping review.

Background: This review aimed to address the growing interest in recycling dental zirconia residues, which are a significant byproduct of the CAD/CAM milling process, contributing to environmental and economic concerns. Further, the review evaluates the potential applications of recycled zirconia in dentistry.

Methods: This scoping review followed PRISMA-ScR guidelines. Eligible sources included peer-reviewed articles, theses, and conference papers, with no restrictions on time or language; unrelated studies and opinion pieces were excluded. A systematic search was conducted across PubMed, Scopus, and Web of Science databases, as well as relevant grey literature. Two independent reviewers handled study selection, data extraction, and qualitative synthesis. Findings are presented in a narrative format with tables and figures.

Results: The search yielded 26 pertinent studies on recycled zirconia, concentrating on recycling methodologies, sintering parameters, and prospective applications. The findings revealed that sintering parameters, including temperature, time, and atmospheric conditions, significantly impacted recycled zirconia's mechanical, physical, and optical properties. The mechanical properties, such as flexural strength, are still lower than those of commercially available dental zirconia. However, the microstructure, density, and shrinkage ratio, alongside the clinically acceptable flexural strength, are encouraging for the clinical adoption of recycled dental zirconia, particularly for short-span bridges. Moreover, the recycled zirconia powder can be applied as fillers in polymethyl methacrylate (PMMA) and as powders for digital scanning.

Conclusion: Recycling dental zirconia is both feasible and beneficial; the utilized recycled materials might be adoptable for clinical applications with optimized recycling processes and sintering parameters. Despite the promising findings, challenges remain, particularly in using mechanical behavior compared with commercially available zirconia.