The aim of this study is the evaluation of powder injection molding (PIM) binder compositions for the material extrusion (MEX) additive manufacturing of zirconia parts. Four commercial PIM binder compositions were selected and mixed with 45 vol% of yttria-stabilized zirconia powder. Due to the brittle characteristic of the obtained ceramic feedstocks, a screw based pellet printing head was used for printing dense zirconia structures. To compare 3D printing performance, additionally a commercially available zirconia filament was used in this study. Application of PIM binder compositions was limited either due to phase separation during processing, poor printing performance or delamination during solvent debinding. Only one of the PIM based feedstock compositions could be successfully printed, debound and sintered. A ring-on-ring setup was used to investigate the equibiaxial flexural strength after sintering for both pellet and filament printed disks. For benchmarking, cold isostatic pressed (CIP) ceramic discs were fabricated by commercial, ready-to-press, zirconia powder. The ring-on-ring results showed a low Weibull modulus (3 <m<5) for all samples, regardless of the manufacturing process. Fractography on selected samples demonstrated, that the origins of failures are close to the area of the loading ring which indicates an uneven stress distribution along the contact area between the setup and the sample. The pointwise stress concentration is the reason for the immature failure of the samples and the low Weibull modulus. The characteristic strength and 90% confidence intervals were used to compare the strength of ceramic samples produced via additive manufacturing and CIP. Almost similar mechanical properties were obtained for the CIP pressed (σ0 = 657 MPa) and filament printed (σ0 = 531 MPa) samples. However, a lower strength was obtained by the pellet printed samples based on commercial PIM Binder (σ0 = 203 MPa). Fractography analysis indicated poor fusion of printed layers for the samples produced with PIM binder composition as the main reason for poor mechanical performance. 

Material extrusion additive manufacturing of zirconia parts using powder injection molding feedstock compositions

Three-dimensionally printed metals and polymers have been widely used and studied in medical applications, yet ceramics also require attention. Ceramics are versatile materials thanks to their excellent properties including high mechanical properties and hardness, good thermal and chemical behavior, and appropriate, electrical, and magnetic properties, as well as good biocompatibility. Manufacturing complex ceramic structures employing conventional methods, such as ceramic injection molding, die pressing or machining is extremely challenging. Thus, 3D printing breaks in as an appropriate solution for complex shapes. Amongst the different ceramics, bioinert ceramics appear to be promising because of their physical properties, which, for example, are similar to those of a replaced tissue, with minimal toxic response. In this way, this review focuses on the different medical applications that can be achieved by 3D printing of bioinert ceramics, as well as on the latest advances in the 3D printing of bioinert ceramics. Moreover, an in-depth comparison of the different AM technologies used in ceramics is presented to help choose the appropriate methods depending on the part geometry.

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3D Printing of Bioinert Oxide Ceramics for Medical Applications

PURPOSE This in-vitro analysis aimed to compare the intaglio trueness, the antagonist’s wear volume loss, and fracture load of various single-unit zirconia prostheses fabricated by different manufacturing techniques. MATERIALS AND METHODS Zirconia crowns were prepared into four different groups (n = 14 per group) according to the manufacturing techniques and generations of the materials. The intaglio surface trueness (root-mean-square estimates, RMS) of the crown was measured at the marginal, axial, occlusal, and inner surface areas. Half of the specimens were artificially aged in the chewing simulator with 120,000 cycles, and the antagonist’s volume loss after aging was calculated. The fracture load for each crown group was measured before and after hydrothermal aging. The intaglio trueness was evaluated with Welch’s ANOVA and the antagonist’s volume loss was assessed by the Kruskal-Wallis tests. The effects of manufacturing and aging on the fracture resistance of the tested zirconia crowns were determined by two-way ANOVA. RESULTS The trueness analysis of the crown intaglio surfaces showed surface deviation (RMS) within 50 µm, regardless of the manufacturing methods (P = .053). After simulated mastication, no significant differences in the volume loss of the antagonists were observed among the zirconia groups (P = .946). The manufacturing methods and simulated chewing had statistically significant effects on the fracture resistance (P < .001). CONCLUSION The intaglio surface trueness, fracture resistance, and antagonist’s wear volume of the additively manufactured 3Y-TZP crown were clinically acceptable, as compared with those of the 4Y- or 5Y-PSZ crowns produced by subtractive milling.

https://doi.org/10.4047/jap.2022.14.2.122

Evaluation of intaglio surface trueness, wear, and fracture resistance of zirconia crown under simulated mastication: a comparative analysis between subtractive and additive manufacturing

The present study comprehensively compared the microstructure, flexural strength, and fracture toughness of zirconia ceramics prepared via two different methods, subtractive milling (SM) and stereolithography (SLA). Disc- or rectangular-shaped zirconia specimens (Prettau (SM) and 3DMix Zirconia (SLA)) were prepared following each manufacturer’s instructions and polished. The microstructures of the two different zirconia specimens were studied by scanning electron microscopy, X-ray diffractometry, energy-dispersive X-ray spectroscopy, and electron backscattered diffractometry. The flexural strength and fracture toughness based on the indentation fracture method were measured for the two different zirconia ceramics. A greater number of small pores and smaller grains were found in the SLA specimen than in the SM specimen. The crystal structure and microstructure analysis revealed that both ceramics had a similar phase composition to each other. No significant differences in flexural strength (p = 0.242) or fracture toughness (p = 0.101) were detected between the two ceramics. The mean flexural strength of the SLA-fabricated zirconia as well as the SM zirconia satisfied the class 5 criteria (>800 MPa) in the ISO 6872 standard.

/pdf/microstructure-flexural-strength-and-fracture-toughness-1m117cgp.pdf

Microstructure, Flexural Strength, and Fracture Toughness Comparison between CAD/CAM Milled and 3D-Printed Zirconia Ceramics

Tooth enamel wear occurs because of daily mastication and occlusion. This study investigated the wear behavior of bovine teeth against aesthetic restorative materials in vitro. Abrader specimens were fabricated using four tooth-colored restorative materials (zirconia, lithium disilicate glass ceramic, dental porcelain, and resin composite), with bovine tooth enamel as a control. Flattened bovine tooth enamel was used as the substrate specimen. These materials were characterized by Vickers hardness tests and surface roughness measurements. Two-body wear tests between the abrader and substrate specimens were performed, and the worn topographies were evaluated using a contour-measuring instrument and 3D laser microscope. The restorative materials and bovine tooth enamel had similar surface roughness but different hardness and wear behaviors. Bovine teeth showed the largest wear in tooth–tooth contact as the abrader and substrate specimens. Compared to bovine teeth, zirconia, lithium disilicate glass ceramic, and dental porcelain showed greater hardness and less wear on their surfaces, and less substrate wear of the opposite tooth enamel. The lowest hardness resin composite showed intermediate wear on its surface, resulting in the lowest substrate wear. Accordingly, dentists should pay attention to the selection of restorative materials to reconstruct their morphologies owing to different wear behaviors.

/pdf/wear-behavior-between-aesthetic-restorative-materials-and-3utu5we2.pdf

Wear Behavior between Aesthetic Restorative Materials and Bovine Tooth Enamel

Additive manufacturing (AM) has many advantages and became a valid manufacturing technique for polymers and metals in dentistry. However, its application for dental ceramics is still in process. Among dental ceramics, zirconia is becoming popular and widely used in dentistry mainly due to its outstanding properties. Although subtractive technology or milling is the state of art for manufacturing zirconia restorations but still has shortcomings. Utilizing AM in fabricating ceramics restorations is a new topic for many researchers and companies across the globe and a good understanding of AM of zirconia is essential for dental professional. Therefore, the aim of this narrative review is to illustrate different AM technologies available for processing zirconia and discus their advantages and future potential. A comprehensive literature review was completed to summarize different AM technologies that are available to fabricate zirconia and their clinical application is reported. The results show a promising outcome for utilizing AM of zirconia in restorative, implant and regenerative dentistry. However further improvements and validation is necessary to approve its clinical application.

Ali Tahmaseb

Papers

Additive Manufacturing of Zirconia Ceramic and Its Application in Clinical Dentistry: A Review.