In a recent article in the magazine Journal of the European Ceramic Societythe researchers discussed the development of fully dense zirconia ceramics printed in three dimensions (3D) by extrusion for dental restorations.
To learn: Extrusion-based 3D printing of full-density zirconia ceramics for dental restorations. Credit: Bencemor/Shutterstock.com
Due to their special properties, zirconium oxide ceramics are of increasing interest in biomedical applications. Zirconia presents a challenge in fabricating a 3D structure with complex geometry due to its exceptionally high chemical inertness and melting temperature. Subtractive computer-aided manufacturing (sCAM) has become the primary method used in dentistry to fabricate zirconia dental crowns and bridges. Although this method is well known and offers several advantages, it also has some disadvantages.
A viable alternative to the limitations of sCAM technology is 3D printing (3DP). Dental ceramics can be manufactured using various 3DP processes. The extrusion-based 3DP technique is considered the simplest and most economical of these technologies. Initial research has produced encouraging results of comparable strength and accuracy; however, there are significant problems with this method that prohibit its acceptance in dentistry. To prevent the overhang structure from collapsing, the system typically requires a support strategy. In addition, the carrier materials must be easy to remove without contaminating the components.
About the study
In this study, the authors discussed the fabrication of detailed, fully dense ceramics based on gelled zirconia suspensions, and an improved extrusion-based 3D printing technique was developed. The viscoelastic properties of the suspensions were adjusted to provide self-supporting characteristics and smooth flow through a 150-250 micron nozzle at a high solids volume fraction of 52%. Due to the low content of organic substances, the freshly dried zirconium oxide samples could be sintered directly without having to remove the binder.
The team showed that the flexural strength, maximum specific gravity and hardness of the sintered zirconia ceramic were 1010 MPa, 99.3% and 15.9 GPa, respectively. By co-printing a unique polyacrylate support material, which could be removed by cooling due to its temperature-dependent rheological behavior, zirconia dental restorations were fabricated while maintaining the occlusal properties. An improved extrusion-based 3DP ceramic technique was developed to create flawless, fully functional ceramics suitable for dental restorations.
Researchers demonstrated that to achieve self-supporting properties, the aqueous suspensions for 3DP containing ZrO2 acting as the ceramic phase were designed with low organic binder content and high solids loading. In addition, a brand new polyacrylate (PAA) gel suspension-based freeze-removable support system has been developed. The rheological properties of both suspensions and the ZrO2 examined the suitability of the suspension for 3D printing. The mechanical properties of the sintered samples under different sintering conditions were characterized after the green bodies of the samples were designed. Tooth crown and tooth specimens were prepared to confirm the feasibility of the procedure.
In order to properly make delicate parts with overhangs, the support was one of the most important components. A new freeze-removable support material scheme was created based on a gelled PAA suspension. This suspension showed temperature-dependent rheological properties and served as a supporting substance in this process. Thus, cooling made it easy to remove the carrier.
Both zirconia and PAA suspensions could be easily 3D printed with the proposed technique. Due to the extremely low organic binder content, the dried zirconia samples could be sintered without the need for debinding processes. The sintered zirconia samples had a flexural strength of 1010 MPa, maximum specific gravities of 99.3% and a hardness of 15.9 GPa. The information showed that the proposed method could produce ceramics from totally thick ZrO2.
In addition, with the right ZrO2, tooth crowns with color and translucency gradients can be produced without time-consuming post-processing2 Suspensions with different colorants or transparency modifiers were synthesized and mixed prior to extrusion. However, the milling process continued to outperform this extrusion-based 3DP ceramic technology. Printing was extremely sluggish and surface roughness was unacceptable.
In summary, this study explained the development of a 3DP technique based on an optimized extrusion for gelled zirconia suspensions. The viscoelastic properties of the suspension were tailored to form self-supporting features and allow flow over a 0.15-0.25mm nozzle with a high solids volume fraction. The ZrO2 The suspension was extruded with an extremely precise progressive cavity feeder. To show how the proposed approach could produce tooth restorations with a complex geometry when used with the PAA carrier ZrO2 Tooth and tooth crown fabrication were performed.
The authors mentioned that the above properties provide good process accuracy for the fabrication of complex ceramic structures. The special composition of the gelled ZrO has opened up a new way of producing flawless, absolutely dense tooth restorations with a comparatively high level of accuracy2 and PAA suspensions and the insight that comes from the effects of equipment and parameters on process precision.
The team believes it is imperative to continue exploring optimization techniques to increase production accuracy and efficiency.
Jiaxiao, S., Xie, B., Zicai, Z., Extrusion-based 3D printing of full-density zirconia ceramics for dental restorations. Journal of the European Ceramic Society (2022). https://www.sciencedirect.com/science/article/abs/pii/S095522192200855X