Zirconia-based materials are widely used in dentistry due to their biocompatibility and suitable mechanical and tribological behavior. Although commonly processed by subtractive manufacturing (SM), alternative techniques are being explored to reduce material waste, energy consumption and production time. 3D printing has received increasing interest for this purpose. This systematic review intends to gather information on the state of the art of additive manufacturing (AM) of zirconia-based materials for dental applications. As far as the authors know, this is the first time that a comparative analysis of these materials’ properties has been performed. It was performed following the PRISMA guidelines and using PubMed, Scopus and Web of Science databases to select studies that met the defined criteria without restrictions on publication year. Stereolithography (SLA) and digital light processing (DLP) were the techniques most focused on in the literature and the ones that led to most promising outcomes. However, other techniques, such as robocasting (RC) and material jetting (MJ), have also led to good results. In all cases, the main concerns are centered on dimensional accuracy, resolution, and insufficient mechanical strength of the pieces. Despite the struggles inherent to the different 3D printing techniques, the commitment to adapt materials, procedures and workflows to these digital technologies is remarkable. Overall, the research on this topic can be seen as a disruptive technological progress with a wide range of application possibilities.

Polylactic acid (PLA) has been used as a matrix material to produce composites with natural fibers, which present several advantages, being one of them the addition of value to agricultural waste. Thus, this study aims to develop a PLA 3D filament with the incorporation of a waste agriculture product (rice husk (RH)). For that, RH fibers were prepared, and PLA was loaded up to 20% RH. The filaments were obtained by extrusion. Finally, samples were produced by fused deposition modeling (FDM). The fibers and filaments’ density and thermal stability (TGA) were determined, and their chemical structure changes due to alkali treatment were accessed by Fourier Transform Infrared Spectroscopy (FTIR). Printability tests were performed, and printed samples were characterized in terms of density, water absorption, and mechanical behavior (compression, tensile, and flexural tests). The results showed that the alkali treatment changed the chemical structure of RH fibers and TGA showed that the filaments did not degrade significantly until 250ºC. The best printability was achieved with 5% of HR content and was the one that showed the lowest mechanical properties reduction. Overall, the present work showed that RH fibers can be successfully used as a filler in PLA filaments for FDM.

This review focuses on the wear mechanisms of natural and restorative dental materials, presenting a comprehensive description and analysis of the works published in the last two decades on the wear at the interface of occlusal surfaces. Different groups of tribological pairs were considered: tooth-tooth, tooth-restorative material (tooth-ceramic, tooth-resin-based-materials, and tooth-metal), and restorative-restorative materials. The lack of standardization of the wear tests impairs the direct comparison of the obtained results. However, it was possible to infer about the main wear mechanisms observed on the different classes of dental materials. Concerning ceramics, their toughness and surface finishing determines the wear of antagonist tooth. Abrasion revealed to be the main wear mechanisms at occlusal interface. In the case of resin-based composites, the cohesion of the organic matrix and the nature, shape, and amount of filler particles greatly influences the dental wear. The protruding and detachment of the filler particles are the main causes of abrasion of antagonist enamel. Metallic materials induce lower wear on antagonist enamel than the other classes of materials, because of their low hardness and high ductility. Most of the studies revealed plastic deformation and adhesive wear as the main wear mechanisms. Overall, more research in this area is needed for a better understanding of the mechanisms involved at the occlusal surfaces wear. This would be essential for the development of more suitable restoration materials.