Sumita Mitra, Inventor of Filtek Nanocomposite Dental Materials at 3M, Inducted into National Inventors Hall of Fame

Dr. Sumita Mitra. From the National Inventors Hall of Fame website.

There are more than 35 million people living in the United States who are missing all of their teeth in one or both jaws, according to statistics published by the American Academy of Implant Dentistry (AAID). Worldwide, there are approximately 1.7 licensed dentists but only about 10 percent of them place dental implants, like crowns or bridges, for tooth restoration. The AAID estimates that 15 million people in the U.S. have had dental operations involving the use of crowns or bridges to replace teeth and another 3 million Americans have dental implants.

Although the population of Americans who are completely edentulous, or lacking teeth, in at least one jaw is generally more elderly, nearly 70 percent of adults aged 35 to 44 have lost at least one tooth due to an accident, tooth decay, gum disease or some other reason according to statistics from the American Association of Oral and Maxillofacial Surgeons. Those statistics also show that more than one-quarter of adults reaching the age of 74 have lost all of their permanent teeth, posing major issues to an individual’s nutritional intake. Individuals with multiple missing teeth also have a higher risk of suffering from diabetes or cardiovascular disease.

While dental crowns and other tooth restoration options typically feature some sort of metallic feature to anchor the implant within the mouth, some tooth restoration work is accomplished with the use of dental composite resins, such as those used in filling cavities. Between 2017 and 2022, the global market for dental composite fillings was expected to increase by a compound annual growth rate (CAGR) of 4.8 percent to exceed $509 million by 2022, according to market analysis firm Research and Markets.

This year, the National Inventors Hall of Fame will be inducting a new class which includes the inventor of a dental composite material which was revolutionary for its high durability and wear resistance compared to other filling materials at that time. This Friday, May 4th, marks the 14th anniversary of the issue of one of the dental filling material patents held by Dr. Sumita Mitra, a former 3M chemical engineer responsible for the development of Filtek dental restorative material. With this patent anniversary upon us, we return again to our Evolution of Technology series to take a long view at the history of dental implants and the impact of Mitra’s contributions to this field of research.

History of Tooth Restoration From Ancient Times Onward

Evidence of tooth restoration extends all the way back to 2500 BC as the ancient Egyptians used ligature wire composed of gold in an attempt to stabilize teeth along the jaw. Two thousand years later, around 500 BC, Etruscans living in the area which today is the Tuscany region of Italy used animal bones to create tooth replacements. Going back two thousand years from today, evidence of dental implants can be found in cultures around the world including those inhabiting regions of Middle Asia, the Mediterranean as well as North and South America. Scientific evidence has also shown that the Mayans were embedding carved bones, seashells and stones into jaws for tooth replacement which actually exhibited the ability to fuse to the jawbone by 600 AD.

Through the Middle Ages, Europeans experimented with tooth restoration techniques involving allografts, tissue grafts from other humans which aren’t genetically identical to tissues in the recipient, and xenografts, tissues grafts from animals. Dental implants collected from cadavers were also employed in tooth restoration techniques during this period of history. These techniques also carried with them the high risk of infectious disease as well as increased risk of mortality.

The use of tooth transplants and metallic anchoring elements would develop slowly over the next few hundred years until World War II when U.S. Army dentist Norman Goldberg, inspired by the work of a Swedish doctor, developed tools and techniques for performing subperiosteal implants, which utilize a metal frame installed under the gum tissue but above the jawbone. Dental implants advanced even further in the late 1950s when Swedish physician Per-Ingvar Brånemark, a 2016 inductee into the National Inventors Hall of Fame, developed techniques for osseointegration which secured dental implants by encouraging the formation of bony tissue to anchor the implant.

Sumita Mitra Uses Nanoparticles to Dramatically Improve Dental Filling Materials

Evidence of the use of dental fillings to restore teeth still in the jaw of patients extends even further before the use of dental implants. In 2012, researchers announced the discovery of a beeswax filling used in dental reconstruction dating back all the way to 4500 BC. Dental amalgam fillings, or metallic alloy mixtures used to fill in teeth, have their origins in China’s Tang Dynasty in the 7th century and were adopted by European cultures in the 16th century. The use of amalgam fillings would increase through the 19th century when such techniques were brought to America but their use would lose popularity with the discovery of the negative health impacts of mercury, a normal component of amalgam fillings.

Dental composites for filling teeth did exist in the 20th century but it would take the contributions of Sumita Mitra to create a reliable composite filling material with high cosmetic and durability characteristics. Mitra joined 3M in 1978 after receiving her Ph.D. in organic/polymer chemistry from the University of Michigan. She would work in 3M’s Oral Care division and by 1998, she attained the position of corporate scientist for the company. Mitra worked with a team of researchers at 3M to develop nanomers and nanoclusters as filler compounds in a composite which could be handled as a paste but could be cured to provide superior long-term optical qualities. Not only was the mixture capable of curing into a material which was indistinguishable from natural teeth but the cured material also had high resistance to fractures and wear.

On May 4th, 2004, the U.S. Patent and Trademark Office issued U.S. Patent No. 6730516, titled Clustered Particle Dental Fillers and one of three patents for which Mitra has been inducted into the Hall of Fame. It covers a filler for dental materials comprising a substantially amorphous cluster of non-heavy metal oxide particles and amorphous heavy metal oxide particles having an average diameter of less than 100 nanometers (nm). The resulting invention provides dental filling materials which are strong, highly aesthetic and radiopaque, allowing for better examination using standard dental X-ray equipment.

Mitra is also being inducted into the Hall of Fame based on her research and development leading to two other patents issued to 3M. In May 2002, the USPTO issued U.S. Patent No. 6387981, titled Radiopaque Dental Materials with Nano-Sized Particles. This patent covers a dental material comprising heavy metal oxide particles having an average diameter of less than 300 nm, an acid modified heavy metal oxide and a hardenable resin. This invention offers similar characteristics to the dental materials developed by Mitra, including high resistance to abrasion. In June 2003, the USPTO issued U.S. Patent No. 6572693, titled Aesthetic Dental Materials. It covers a material comprised of a hardenable resin and a filler composed of nano-sized particle clusters of heavy and non-heavy metals which are not fully densified as well as non-agglomerated nano-sized heavy and non-heavy metal oxide particles.

Filtek Supreme Restorative, the commercial dental filler material based on Mitra’s work, was first introduced to the market in 2002 and new generations of the product have been introduced in 2005 and 2012. According to Mitra’s entry in the National Inventors Hall of Fame, Filtek products have been used in 600 million tooth restorations worldwide. Before retiring from 3M in 2010, Mitra would go on to obtain 98 patents covering a variety of composites used for dental procedures. She continues to work in the field of chemical engineering through her work with Mitra Chemical Consulting, which she runs with her husband Sam.