Identifying a novel approach to improving the fit of 3D-printed dental restorations 

University of Perugia Research Fellow Dr. Giulia Pascoletti and Professor Elisabetta Zanetti explore the future of dental 3D-printing materials  

3D printing continues to grow in popularity among dentists around the world. The technology allows for the faster in-lab production of custom manufacturing of crowns, bridges, and aligners. But desktop 3D printing is far less established than traditional molding in the dental field. While there are many reasons for this, it’s largely due to a lack of available materials.  

For those unfamiliar with 3D printing, it’s not unusual for materials to be “qualified” for manufacturing. This means identifying a set of parameters that consistently delivers desired results. Challenges to qualifying new dental resins include speed, biocompatibility, and of course, sample size. It’s also essential to get geometric accuracy spot-on: poorly fitted implants can come loose, necessitating another trip to the dentist or even leading to infections.  

Coming up with a solution requires a balance between precision and efficiency in R&D. This is no mean feat, but our team at the University of Perugia (https://www.unipg.it/) is now making progress. As part of a nationwide initiative, we’re working on ways to automate metrology at our Smart Manufacturing Laboratory. This has led to the development of an enhanced workflow, currently built on intraoral scanning, but we see a lot of potential for 3D scanning to accelerate qualification even further.   

Methodology  

Early testing has revolved around Zirconia 5Y and 8Y, two promising ceramic candidates, and our goal was simple: using the tools in our new metrology lab to identify deviations between nominal and realized shapes. As readers will appreciate, checking for defects is important as they can lead to cracks, which develop into breakage — so fit and mechanical integrity were prioritized.  

We started by digitizing reference samples with a 3Shape Trios 5 (https://www.3shape.com/en/scanners/trios-5) intraoral scanner. These were later compared to samples 3D printed with a commercial SprintRay Pro digital light processing (DLP) system (https://sprintray.com/pro2-dental-3d-printer/). We had to tune many parameters to get the best possible results, including print speed, temperature, and humidity, but after some trial and error, we found a good balance.  

Captured scans were eventually sent to CloudCompare, an open-source cloud processing software, for alignment, registration, and deviation analysis (https://cloudcompare.org/). Statistical analysis was carried out in MATLAB, a program with more advanced tools that’s better at crunching complex datasets (https://www.mathworks.com/products/matlab/data-analysis.html).  

Results  

 Initial results showed clear performance differentiation between tested materials. Standard deviation was much higher in one set of samples than the other. Spatial distribution analysis (visualized in the form of color maps) also showed that weak points were distributed differently across occlusal and bottom surfaces. One day, this data could be valuable for identifying design weak points, improving the crown-tooth interface, and avoiding implant failure.  

Both materials also met minimum stability requirements, making them potential candidates for future end-use applications. The project is still ongoing — two further zirconia materials are now being analyzed in our lab, with results looking similarly promising. This testing is being carried out using an Artec Micro II 3D scanner in place of our intraoral scanner (https://www.artec3d.com/portable-3d-scanners/artec-micro). Provided by 3DZ, a known player in the Italian dental 3D printing space, the device offers improved precision (https://3dzgroup.com/).  

Micro II automatically digitizes objects, projecting white light patterns onto surfaces mounted on a platform, which twists and turns to ensure complete data capture. Already, this desktop unit is accelerating our workflow, picking up enough data in one sweep, without us needing to use technologies like X-rays and optical tomography for deeper inspection. Its enhanced precision also allows for a broader range of deviations to be found – and unlocks further fine tuning. 

Conclusions  

We see significant potential for our approach in the biomechanical evaluation of dental manufacturing discrepancies. With additional research, we believe it’ll also be possible to test other factors such as wear and tribology. This will lend greater clarity to R&D and help bring new materials to users, including those using 3D printers at their clinics for in-house production.  

Moving forward, we plan to continue experimenting. We’re currently working on auto-viewpoint generation, for example, which calculates the minimum number of scans needed from each position for high-quality models. Ultimately, we aim to accelerate material qualification. In order to achieve this, we need to fully understand how each parameter, whether it be print speed, temperature, or shrinkage, affects the implant manufacturing process. 

At the beginning of our research, it seemed that it would be impossible to find resins that are both malleable enough for 3D printing, and sufficiently resilient for making robust implants. Our promising early results show that this is possible with certain parameters and ceramic formulations. Continuing to work with public and private partners, we’re confident of developing our approach further, and shedding new light on the potential of 3D printing in dental.  

The research project “3D printing and digital twinning ceramic restorations for dentistry” (3DCer4Dent) is being carried out with funding from the Italian Ministry of University & Research (as a PRIN initiative) with Next Generation EU backing (J53D23012190). 

Project contributors include several schools in Italy: Dental School at the University of Turin, Turin Polytechnic, the University of Catania, and the University of Perugia. Those seeking more information can reach out directly to Prof. Elisabetta Zanetti at elisabetta.zanetti@unipg.it. 

What does this mean for dentists?  

To get a better understanding of their research and its potential impact in dental, we also spoke with Prof. Nicola Scotti at the Dental School at the University of Turin, who participated in the study. 

What can be 3D printed from ceramic? 

The 3D printing of dental ceramics is still experimental. No material has been certified for clinical use, but promising results have been obtained using 3D-printed zirconia with different amounts of yttria (yttrium oxide Y2O3). Lithium-disilicate is also 3D printable, but still far from minimal standards. Nowadays, polymers with ceramic fillers are easier to process with 3D printing.  

How do these compare to traditional materials?  

Dental zirconia and lithium disilicate restorations are traditionally obtained through milling processes, which presents some limitations, including tensions during milling, limited geometries, difficulties in reproducing anatomical details, and material waste. 

How do you plan to use 3D scanning in the future? 

Scanning is now recognized as the best way to register teeth and manufactured product analysis — and it’s better integrated with technologies that allow for intraoral and extraoral impression. In the future, the use of 3D scanning will be useful for diagnosis, measuring dental wear, and patient monitoring over time.