Interview: Marta Kazmierowska On Metal 3D Printing in Dentistry

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Marta Kazmierowska graduated from Hunter College, the City University of New York, with a Bachelor’s degree in chemistry. After returning to Poland she pursued a Master’s degree in green chemistry at Gdansk University of Technology. During her second degree studies, she gained extensive practical knowledge about various 3DP technologies. She practiced at LITHOZ in Vienna where she worked with the lithography-based ceramic manufacturing (LCM), and in Pomeranian Science and Technology Park in Gdynia with selective laser sintering (SLS) and PolyJet technology. Right now she is a CAD/CAM supervisor and EOS M100 operator at a dental prosthesis laboratory. She is interested in all 3D printing technologies and their application in medical and non-medical fields. In her free time, she is building anatomical models from CT data.

Before I discovered 3D printing (3DP), I had several work experiences. In college, I worked as an assistant in a chemistry laboratory and in a pharmacy. I had also previously been a babysitter, a secretary and later on a teacher in an international school. Each of these jobs provided me with different and rich experiences that shaped my personality and way of thinking. However, for me, none of these experiences were truly fulfilling, truly absorbing, or my own… I felt that I was doing things that were already established by somebody else, sort of a template that I’d fill in. And I had an everlasting feeling that I need to do something innovative. I decided to quit the teaching position I had and enrolled on a master course at the Gdansk University of Technology. I quickly found a mentor and during one of our conversations she mentioned 3DP. I started researching the topic – I was mesmerized. That was it! There was one more thing that I knew right away, there is no time to waste! I need practice, practical knowledge, hands-on experience, not only dry facts from books. Through my professor, I contacted amazing people at LITHOZ in Vienna and left for a three-month practice. That experience was one in a lifetime, I gained knowledge, experience and I made true friends. When I came back to Poland, I saw that the 3DP Lab in the Pomeranian Science and Technology Park in Gdynia was opened, so I went there and asked if I could do some volunteering. I was lucky, again. The people were kind and open to share and exchange their knowledge.
The freedom, almost limitless possibilities of different 3DP techniques and the people from the field inspire and motivate me every day. I want to use and spread the power of 3DP to people’s advantage because many things can be done better, faster and generate less waste.
Therefore, I’m happy to be a CAD/CAM supervisor and EOS M100 operator working with CoCr at the dental prosthesis laboratory in Gdansk. I embarked on a mission to convince people from the dental and dental prosthesis field about advantages of the innovative CAD/CAM technologies with the focus on 3D printing.
Creation of precise, fully-functional and biocompatible metal crowns and bridges using conventional lost-wax casting methods is a laborious, multi-step, and time-consuming process, which may not always produce high-quality dental prosthesis parts. The errors can occur at early stages, during impression collection at the dentist, and build up during wax modeling, during metal casting, and during post-processing. The casting process by itself is difficult to control. As a result, the obtained part can have many irregularities, gaps, and air bubbles, which complicate and extend the post-processing step. Also, thick casting sprues, which are directly melted with the crowns, have to be cut away and the surface of a crown have to be polished.

Fig.1. 6-point bridge and one crown obtained with the conventional lost-wax casting technique. Irregular surface, air bubbles, thick and heavy sprues require laborious and time-consuming post-processing, which also generates a lot of waste.

A metal crown that is too tight, too loose or doesn’t fit on a model, is a nightmare that can happen to the most skilled and experienced dental prosthesis technician. Additionally, when producing big and multi-pontics bridges, there is a high chance that they will bend. Another disadvantage of the conventional metal casting is waste production.
Innovative CAD/CAM technologies allow to: collect precise digital impressions, and then design and produce very detailed metal crowns and bridges. The intraoral scanners are more comfortable for the patient since no goopy, short-lived impressions are needed. The entire scanning procedure happens in real-time at the dentist’s office. A doctor, in a split of a second, electronically sends obtained scans to a dental prosthesis CAD/CAM department, where specialized technicians make projects of metal crowns and bridges on the computers. The scans and projects can be stored and accessed at any time, eg. for retrospective studies, whereas most of the impressions can be only used once. The digital impressions can also be 3D printed in eg. digital light processing (DLP) technology. The 3DP models are more detailed than the gypsum models and almost no waste is generated during their production. If the dentist’s office doesn’t have an intraoral scanner, conventional impressions can be sent to our laboratory. In this case, we make our .stl projects by scanning gypsum models.
Obtained .stl project is then analyzed in additional programs, which check for errors in a digital net, orient the part and generate the support structures. Once the part and its support structures are ready, they are transferred to the EOS M100 printer which uses the direct metal laser sintering (DMLS) 3DP technology.

Fig.2. EOS M100 printer which uses the direct metal laser sintering (DMLS) 3DP technology.
M100 produces precise, high-quality, high-density metal crowns and bridges in a matter of few hours with no human interference. The parts are built in a layer-by-layer fashion, by application of a thin metal powder layer by the ceramic coater and exposition of layers by a high-intensity ytterbium laser.

Fig.3. Ytterbium laser tracing and melting the contours of support structures on a thin surface of the evenly distributed powder.
Fig.4. Metal crowns and bridges produced on an EOS M100 printer in the DMLS technology. The detail of the parts is precise due to scanners which replicate exact morphologies of patient’s teeth and due to 30µm printing layer thickness. The surface of parts is smooth and easy to finish. More than 80 metal points can be produced in a single cycle!
After the finished run, the printer is carefully cleaned. The biocompatible, medical-grade CoCr powder is screened on a sieve of a specific size and reused in next cycles. Therefore, almost no waste is produced because only the material that is needed for the part and its supports are used. The parts on a building platform are then sanded and placed in the oven. The thermal treatment in the inert Ar atmosphere gives parts final structural properties and reduces the tensions so the probability of twisting and bending is minimal. After the thermal cycle, the parts are detached from the building platform and undergo post-processing. The support structures have a form of small pins they do not go deep inside the part. Therefore, they can be easily removed with pliers by a squeezing and twisting motion. Once the supports are removed, the parts need surface polishing and quick sanding, since the surface of printed crowns and bridges is already smooth and regular.

Fig.5. A Precise, detailed and smooth surface of DMLS metal dental prosthesis parts together with tiny, easy to remove support structures.
Due to the exact and detailed image obtained with a scanner and thin printing layer (30 µm) the fitting of even the biggest 14-point bridge is almost perfect, so no laborious fitting on the model is needed. Such parts are ready to be used for eg. porcelain application. Due to the precise DMLS technology, the density of produced metal crowns and bridges reaches almost 100% so there is no gassing during the porcelain application process.

Fig.6. Building platform with CoCr crowns and bridges.
Thanks to the innovative CAD/CAM technologies we are able to produce in one cycle more than 80 metal points in a matter of few hours! And we are able to do more than four cycles a day! Therefore, this technique minimizes the errors, amount of work and waste, producing a large number of high-quality parts in less than a workday!
I speak with dentists and dental prosthesis technicians on a daily basis and try to convince them to these innovative approaches. I believe that big and small obstacles can be overcome because of a wide variety of options and solutions that are recently available on the market. Every day these solutions expand and right now are at a hand’s reach and they don’t have to be costly. Therefore, I’m motivated to speak to doctors and technicians and make small steps towards creating better future for them and their patients.

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