The European Patent Office (EPO) announces that the Indian-American chemist Sumita Mitra has been nominated as a finalist in the “Non-EPO countries” category of the European Inventor Award 2021. Mitra was the first to apply nanotechnology to the production of dental materials, leading to the creation of a new composite to repair teeth which have many advantages over conventional materials.
Mitra's material overcomes many of the limitations of previous dental composites, which were either too weak to be used on biting surfaces, or quickly lost their polish and became physically unattractive. In addition, her invention is more versatile than other composites, meaning it can be used in any area of the mouth and simplifies the filling procedure for dentists. Commercialised as Filtek Supreme Universal Restorative since 2002 by 3M, the US multinational for whom Mitra worked for more than 30 years, the technology and the products developed from it are today used by dentists around the globe.
“Mitra's invention takes what was an emerging technology at the time — nanotechnology – and applies it to a new sector to provide a solution for dentists and relief for patients,” says EPO President António Campinos, announcing the European Inventor Award 2021 finalists. “Patents have protected Mitra's material and helped ensure that her invention remains commercially successful nearly 20 years after its launch.”
The winners of the 2021 edition of the EPO's annual innovation prize will be announced at a ceremony on 17 June which has this year been reimagined as a digital event for a global audience.
Making a new nanomaterial
Until the late 1990s, dentists wishing to perform natural-looking tooth repairs relied on a combination of two materials: composite microfills, which were aesthetically pleasing but too weak to be used in teeth towards the back of the mouth and biting surfaces; and stronger, but less attractive hybrid composites. A key problem was the size of the filler particles which are suspended in the resin to impart it with strength, colour, and opacity. Traditionally, these fillers consisted of dense, large particles, such as quartz or glass, milled down into finer particles – but as the resin gradually wore away, these particles begin to protrude from the material or were plucked from its surface, resulting in bumps and craters which scattered light. The result was a filling that quickly lost its reflectivity and polish.
It was while working in the oral care division of US multinational 3M that Sumita Mitra became aware of the limitations of existing composite materials. At the same time, nanotechnology was emerging as a field of research and Mitra decided to explore how these new developments could be applied to dentistry. She began working on nanotechnology-based solutions for new dental material, driven by a desire to use her expertise in polymer chemistry and materials science to develop inventions that solve real-life problems for people.
Mitra's idea was to replace composite fillers with nanoparticles – ultrafine particles measuring between 1 and 100 nanometres in diameter – which are smaller than the wavelength of visible light and do not, therefore, scatter it, resulting in a material that retains its shine. At first, Mitra and her team at 3M incorporated uniform nanoparticles measuring less than 20 nanometres in size (1 nm is a billionth of a metre) into resins, but although the materials they created were strong and attractive-looking, they were difficult to mould, making them unsuitable for dentistry.
She and the team, therefore, developed a technique for creating linked clusters of nanoparticles, which they called ‘nanoclusters', combining these with a single nanoparticle of varying diameters, resulting in a strong, durable and shiny material, with excellent handling properties. By adding tiny amounts of pigment, and altering the chemical composition of the nanoparticles, the team also created a range of different shades, which can be matched to individual patients' teeth, and layered to create a more natural finish. “The use of nanotechnology gave me the opportunity of making a new material,” says Mitra. “It restores peoples smiles and improves the quality of their lives”.
Following the successful development process, Mitra worked closely with 3M's patent attorneys to construct the patents to protect her ground-breaking work. Besides her contribution to the Filtek range, Mitra is named as an inventor on 58 granted European patents for inventions that have resulted in various dental innovations including resin-modified glass ionomers and new adhesives which can be found in other 3M products. “The patent was essential for safeguarding the invention so that others could not infringe on the technology,” she says.
Lasting impact in dentistry innovation
The material based on Mitra's work, Filtek™ Supreme Universal Restorative, was launched by 3M in 2002 and, although several new generations have been developed since the current line of products is still based on Mitra's European patents. 3M regards the material as unique because it combines durability with aesthetic qualities not reached by competitors' products which rely on micro- or nano-hybrid fillers instead.
Mitra's invention has contributed to the company being named as one of the top three manufacturers for the global composite filing in the dental restoration market in 2019. The material's strength is its versatility according to her: “You have all the desired properties of a tooth filling in one material. That is why this technology has been used to make so many different types of tooth restorations around the world.”
Although Mitra retired from 3M in 2010, the enduring success of her invention continues with Filtek products used in one billion tooth restorations worldwide by dentists to date. Today she continues to contribute to research and development through her own consulting company. She also volunteers in her community and hopes to inspire young people to develop an interest in science.