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Wanted: Research on 3D-printed zirconia restorations

There is great need for research when it comes to zirconia restorations, regardless of the manufacturing process. (Image: Gorynvd/Shutterstock)

JAZAN, Saudi Arabia: Zirconia-based restorations, renowned for their durability and aesthetics resembling natural teeth, have gained popularity over the past 20years and are increasingly being produced using CAD/CAM. A recent systematic review and meta-analysis comparing milled versus 3D-printed zirconia prostheses has found continual gaps in the research, including biases, and potential underrepresentation of the performance capabilities of 3D-printed restorations. A complete lack of clinical studies on the efficacy of 3Dprinted zirconia crowns and fixed dental prostheses (FDPs) also highlights how far research into zirconia crown fabrication has yet to go.  

Zirconia, dubbed “ceramic steel” for its robustness, is a preferred choice for various dental restorations owing to its high strength and biocompatibility, among other attributes. The introduction of CAD/CAM technologies has enhanced the precision of manufacture of zirconia restorations by minimising human error. There are two main fabrication methods: subtractive (milling) and additive (3D printing). Each technique has its advantages. Milling is cost-effective and less sensitive to minor design imperfections, while printing offers more design flexibility and efficiency in intricate structures. While 3D printing of dental restorations is nascent, studies comparing the effectiveness of milled versus printed zirconia are scarce.  

The present review was conducted in an effort to bridge this knowledge gap by seeking to determine whether the performance of zirconia crowns and FDPs produced by both methods compares favourably with that of conventionally produced ones. The review included various in vitro studies, necessary in lieu of any available clinical studies on 3D-printed zirconia restorations, and the results are intended to guide clinicians in selecting the best method for creating crowns and FDPs. The included articles were published from 2004 to November 2022 and reported on the placement of over 1,500 zirconia restorations, predominantly in the posterior regions. The studies involved a variety of clinical designs, and most patients were followed for over a year.  

Clinically, zirconia crowns and FDPs showed impressive biological and physical properties, with few reported issues. The meta-analysis revealed that, regardless of variables like age, glazing/staining, location and marginal integrity, the pooled survival rate of these crowns and FDPs was consistently high, at 100%. In the context of in vitro studies comparing 3D-printed and milled zirconia crowns and FDPs, findings suggested that both methods offered comparable accuracy, adaptability and strength, positioning 3D printing as a viable option for clinical use. 

The main biological outcome observed across the board was bleeding on probing. Technical issues, such as crown fractures, were noted, one study recording a survival rate of 91.5%. Proper polishing was found to reduce the chance of crown fracture. Other key findings in the review were that patients with bruxism should be treated with zirconia crowns and FDPs with great caution and adjustments might be needed after crown placement owing to occlusal issues or pain. The average preservation of marginal integrity was high, but varied depending on the study. Zirconia was found to cause wear on opposing teeth, but less so than other ceramics.  

There is limited literature on zirconia’s aesthetic aspects, especially concerning colour. The review faced challenges like technique variability and limited patient sample size. Conclusively, zirconia crowns and FDPs, whether 3D-printed or milled, are promising but require more extensive research, especially long-term studies, to validate their benefits over traditionally produced prostheses. Although in some cases the literature suggests that milled crowns and FDPs are superior to 3D-printed ones, there were no identified direct comparisons performed in any studies. The lack of research into 3D-printed crowns and FDPs may have contributed to this result. 

The study, titled “Clinical effectiveness of 3D-milled and 3D-printed zirconia prosthesis—a systematic review and meta-analysis”, was published on 27 August 2023 in Biomimetics 

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