Evaluation of microstructure and mechanical properties of PMMA Matrix composites reinforced with residual YSZ from CAD/CAM Milling process

Abstract

Background: Reinforcement of dental acrylics with fillers has yielded positive results. Different proportions of fillers have been added to strengthen the dental acrylics, but no consensus has been reached. Aim: The purpose of this study was to investigate the effects of the addition of different concentrations of yttria-stabilized zirconium (YSZ) obtained from the residues generated from the CAD-CAM milling of YSZ on the microstructure and mechanical properties of poly-methyl-methacrylate (PMMA)-YSZ composites. Materials and methods: Composite materials with different amounts (0.0 to 70.0% by weight) of recycled YSZ reinforced PMMA resin matrix were produced. Scanning electron microscope (SEM), energy dispersive electron spectrometer (EDS) and Fourier Transform Infrared Spectrometer (FTIR) were used for microstructural analysis. Among the mechanical properties, the Vickers microhardness test method for hardness, 2D profilometer for surface roughness and composite densities were evaluated by Archimedes method. Data were analyzed using a one-way analysis of variance (ANOVA) at a pre-set alpha of 0.05. Results: Microhardness and density increased until 60% by weight YSZ addition, while surface roughness remained unchanged but increased after 60% by weight YSZ addition. The addition of more than 60% by weight of YSZ caused agglomeration in the microstructures. The mechanical properties of poly-methylmethacrylate decreased with more than 60% YSZ by weight. Conclusion: Reinforcement of PMMA with residue zirconia powder will increase the usage chance of residue YSZ powder and provide a safer use of PMMA.

Current prospect of dental zirconia recycling: A scoping review

“…Moreover, if recycled zirconia is not suitable for producing dental prostheses, it can be utilized in other applications while maintaining its high value. For instance, owing to its good chemical resistance and thermal stability, recycled zirconia powder has been used as a reinforcing filler to improve the mechanical properties of PMMA [33].…”

“…PMMA is commonly used in dentistry to make denture bases, but its low mechanical strength makes it prone to fractures [42][43][44]. Previous studies demonstrated that incorporating recycled zirconia powder into PMMA can increase its mechanical strength by enhancing the physical molecular interactions between the PMMA matrix and zirconia through hydrogen bonding and van der Waals forces [33,34,45]. The strength of PMMA may not necessarily increase in direct proportion to the quantity of zirconia powder added, as excessive filler can disrupt the continuity of the resin matrix, leading to a decrease in the strength of the reinforced PMMA [33,34].…”

“…3). The predominant zirconia material used for recycling is 3 mol% Y-TZP (3Y-TZP) [4][5][6][11][12][13][25][26][27][28][29][30][31][32][33]. Among the included studies, one was published in Chinese [6], while the others were published in English.…”

“…Ten studies focused on examining the direct recycling of dental zirconia residue powder [4,[11][12][13]25,26,30,31,33,34]. Six of these studies involved pressing the recycled zirconia powder into green zirconia bodies, which were then sintered [4,[11][12][13]25,30].…”

“…Six of these studies involved pressing the recycled zirconia powder into green zirconia bodies, which were then sintered [4,[11][12][13]25,30]. Two studies utilized recycled zirconia powder as reinforcing fillers in polymeth-ylmethacrylate (PMMA) [33,34]. One study successfully produced nanometer-sized zirconia powder from recycled zirconia powder through ball milling [31].…”