Women in dentistry: Meet chemist and awarded dental materials inventor Dr. Sumita Mitra

Franziska Beier, Dental Tribune International

Wed. 11 August 2021

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As the second candidate for a series portraying outstanding women in dentistry, Dental Tribune International (DTI) interviewed Dr. Sumita Mitra. During her career at 3M, she developed a unique nanomaterial-based dental filler, for which she received the European Inventor Award 2021. This material and numerous other inventions of hers in the field of dental materials have been patented. DTI spoke with Mitra about how a bunch of grapes inspired her research efforts, about the greatest advantages of her developed material and about how she gives back to the next generation of inventors.

Dr. Mitra at the 3M Innovation Center in Minneapolis in Minnesota in the U.S. (Image: European Patent Office)

Dr. Mitra, thank you for agreeing to this interview. Could you tell us something about your background?
I grew up in India and had my early education there. I did my BSc at Presidency College in Kolkata with chemistry honors. After my MSc in chemistry in India, I came to the U.S. and obtained a doctorate in organic/polymer chemistry in 1977 from the University of Michigan in Ann Arbor. After a year of postdoctoral work at Case Western Reserve University in Cleveland in Ohio I joined the 3M Corporate Research Laboratories in 1978 and later moved to the 3M Dental Products Division (now 3M Oral Care) in 1983. There I held positions of increasing responsibility and in 1998 was appointed corporate scientist, the highest technical position at 3M. I led the new materials/products research and development efforts until my retirement in 2010. From 1999 to 2010, I also served as the industrial director of the Minnesota Dental Research Center for Biomaterials and Biomechanics at the School of Dentistry at the University of Minnesota in Minneapolis. Currently I am a partner at Mitra Chemical Consulting, an independent consulting firm, which I co-founded.

Why did you decide to go into chemistry and how did you become concerned with dental materials?
From a very early age I was fascinated by different materials. I often wondered what makes one material different from another—things like why paper is different from wood, or why fabric is different from our skin. I learnt that the answer is in the molecules—it is chemistry that is the central science that defines materials. I was so awestruck by the subject that I made up my mind to study chemistry in depth. I would often visit my father in his laboratory and peer over his shoulders as he did his chemistry experiments. After I joined the 3M company, I got an opportunity to join its Dental Products Laboratory to develop new polymer matrices for dental composites. I jumped at that prospect and spent most of my career there, developing many new materials technologies, including the development of nanotechnology for use in dentistry.

You have developed a nanocomposite restorative material (Filtek Supreme, 3M), that has already been used for more than 1 billion tooth restorations. How did you come up with the idea of using nanotechnology?
Until the late 1990s dentists wanting to perform natural-looking tooth repairs relied on a combination of two separate materials. Microfills were esthetically pleasing but too weak to be used for stress-bearing regions of the incisal edges and for filling teeth in the posterior region of the mouth. Less attractive hybrid and microhybrid composites were stronger, but lost their shine and became rough from brushing and chewing. This was both inconvenient and expensive for dentists and their patients. So, we wanted to create one material that would not only be strong and durable but also have the long-lasting lustrous beauty of natural teeth.

“Everyone has the power to become an innovator”

I realized that the key problem was that the existing filler technology used to reinforce dental composites had limitations. Around that time, nanotechnology was an emerging science. I hypothesized that developing nanoparticle technology for use as dental fillers could allay most of the problems and afford us a universal filling material. This is because nanoparticles are much smaller in size than the wavelength of light and thus could provide unique esthetic properties. In addition, nanoparticles had the potential of providing mechanically strong materials. With this idea, and with the help of a team of 3M scientists, I set about the task of developing suitable nanofillers and incorporating them into a resin matrix to generate nanocomposites with superior characteristics.

Our initial approach was to make tiny nanoparticles of several sizes, but this approach was disappointing since it did not provide all the desirable characteristics, especially the required rheology or handling properties needed by dentists. I realized that this was because we needed nanoparticles of a wide size distribution to get packing efficiency in the composite. It sounds simple but was not easy to achieve with the initial nanoparticles.

Together with scientists at 3M, Dr. Mitra invented the nano-based filling material Filtek Supreme. (Image: European Patent Office)

The decisive idea for the material was inspired by a particular fruit. Could you tell us more about this?
The breakthrough moment came as I was looking at a cluster of grapes in a bowl. If one observes a bunch of grapes, there are grapes of different sizes, some small and some large, with the small ones fitting in between the gaps created by the large ones, leading to optimum use of space. Also, the sizes of the bunches can vary greatly—there can be clusters of five, 20 or 100 grapes, and so on. If one or two individual grapes are plucked out, the overall cluster doesn’t change that much. My theory was that we could first assemble the nanoparticles into nanoclusters of wide size distribution and then combine them with individual nanomeric particles to fill any voids to provide a synergistic mix that could then be incorporated in a dental resin to create the composite. This is what I set out to do, with the help of the excellent team at 3M.

The end result of all that hard work is the universal filling material 3M Filtek Supreme. Since the original material was introduced in 2002, several updates have been made and a family of Filtek products has been introduced for the benefit of dentists and their patients.

Would you please explain how the material works exactly and what some of its greatest advantages for dentists and their patients are?
The 3M Filtek Supreme product is an uncured composite paste, which comes in a number of shades that make it possible to exactly match the patients’ dentition. After using a dental adhesive, the dentist places the composite and shapes it according to the required anatomy, finally curing it in place by a short exposure to blue light. The greatest advantage is that the material is very versatile and can be used in all areas of the mouth—anterior, posterior, and on incisal or molar surfaces. It is highly esthetic and has the shine and opalescence of a natural tooth. It is extremely durable and withstands the forces of chewing and brushing without losing its shine for a long time. Dentists all over the world have expressed their enthusiasm and shared examples of their work, which is very gratifying.

Dr. Mitra loves art and enjoys painting with watercolors in her free time. (Image: European Patent Office)

Your material has been patented. Aside from this product, do you hold any other patents for dental applications?
I hold 100 U.S. patents, 58 European patents and their corresponding equivalents in other countries. The majority of my patents are in the area of dental materials.

You have been awarded and honored many times, including being inducted into the U.S. National Inventors Hall of Fame in 2018. Only recently, you won the European Inventor Award 2021—in the category Non-European Patent Office countries. Congratulations! How meaningful are these awards to you?
I feel greatly honored to be recognized by organizations like the National Inventors Hall of Fame, the American Chemical Society and many others, including most recently the European Patent Office for this invention. It is quite humbling to be included in the same league as so many well-known inventors whose work has greatly benefited society. This type of recognition validates the importance of the scientific contributions of scientists and increases public awareness of the pivotal role that science and technology play for the advancement of society. Another important aspect is that the award creates role models for aspiring scientists who pursue careers in science, technology, engineering and mathematics (STEM)-related fields. Furthermore, awards like these give a voice to science and help in influencing greater funding for scientific research and policymaking.

In your opinion, what are the essential characteristics that a person needs in order to start an innovation?
Basically, it is a combination of curiosity, exploration and imagination. Of course, you need a scientific training, but above all, you have to try new ways of doing things—a way that is more convenient and or easier. The other thing is to have passion coupled with persistence. The first attempts may not be successful, but failures should never discourage us. They only show us that there is another pathway toward achieving a goal.

How do you inspire young people and what would you tell the next generation of potential innovators?
After my retirement, I have spent many hours volunteering and teaching at a number of local organizations, encouraging STEM education at all levels, primary school to postgraduate. It is a way for me to give back to society for all the opportunities I have had.

Everyone has the power to become an innovator. The important thing is to understand that a solid foundation in STEM-related fields gives young people the toolset to unleash their creativity and design better approaches to improving the well-being of society. I always tell young people, “Believe in yourself, seek help when needed, and never give up.”

Editorial note: The first part of the series, featuring dental technician and senior researcher Dr. Joanne Choi, can be accessed here.

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