For centuries, people have used all kinds of materials for bone or dental repair, such as gold, ivory and plastic. 'Much more than before, we are now developing materials from biological knowledge of the body,' says Professor Sander Leeuwenburgh. 'By now we can even administer targeted drugs, such as antibiotics, via very small particles.'
Cavities in teeth have existed for a very long time. The oldest evidence of a hole in a molar and an attempt to treat it is 14,000 years old. A molar found in a cave in northern Italy shows traces of someone who tried to scrape away the rotten part of the tooth with a sharp stone. Filling cavities also goes very far back in history. The very first filling was found in a 6,500-year-old fossil jawbone in a cave in Slovenia. In it, a damaged canine tooth had been filled with beeswax. So that's the oldest known patchwork in dentistry.
Dentures with horse teeth
'The use of materials to fill teeth or bone goes back thousands of years and is of all cultures,' says Sander Leeuwenburgh, professor of Regenerative Biomaterials. 'The Egyptians, Chinese and Incas, for example, were very active and tried everything that was available: ivory, bamboo, gold, lead. Because these materials replace biological tissue, today we call them biomaterials. The use did not always go well; lead, for example, is too toxic.'
The oldest known denture dates back to the Renaissance. It consists of five teeth from different people. The teeth were attached to each other with metal wires. A few centuries later, George Washington was a famous wearer of a whole collection of dentures. When he became president of the United States in 1789, he had only one tooth of his own. His dentures consisted of teeth from humans and animals such as horses, held together by bronze and gold.
World War II gave a boost to the development of new high-performance materials, including plastics such as plastic. Those materials were initially developed to make lightweight parachutes, for example. But they also turned out, often by accident, to be very suitable as biomaterials in the human body. Sander: "For example, plastic has been successfully used to repair bones or blood vessels. These plastics were cheap, light, strong and long-lasting. They also found their way into dentistry, as dentures are still made of plastics.'
After the war, the development of materials continued. So researchers tested different types of metal, ceramics and plastics, all with their own advantages and disadvantages. But what are the latest developments? What are the biomaterials of the future? Sander: 'They will be designed much more than current materials, based on knowledge of biology and the functioning of the human body.'
From filler to tool
'Nowadays we often develop materials that consist of multiple components, just like bone itself,' explains Sander. 'These ingredients are similar in composition to the components of bone, which is made up of a mix of hard and soft nanoparticles. These particles, even smaller than a bacterium, offer the great advantage that you can load them with biologically active substances, which, for example, promote bone repair and combat bone diseases.'
The biomaterial then serves not only as a filler, but also as a tool for very local administration of drugs. For example, addition of antibiotics to biomaterials can treat infections around implants. Biomaterials can also deliver anti-cancer drugs, so that tumor cells left behind after tumor removal still die. And substances that promote growth (so-called growth factors) stimulate the growth of the surrounding healthy bone.
Just like in the ball pit
Future biomaterials will not only consist of different kinds of particles, but they can also be much more flexible and soft. Sander: "For a long time, researchers thought that biomaterials must necessarily be hard, just like bone. But the hardness of the current generation of biomaterials means that they often break too quickly. Moreover, bone arises from a soft precursor phase. So we now imitate that more, for example, by building up biomaterials entirely from nanoparticles.'
'You can compare these new biomaterials to a ball pit,' Sander explains. The balls move past each other and therefore the material can deform quite easily. When a child crawls through the balls, they move aside. In this way, hopefully, cells can also crawl between nanoparticles.'
Those cells can come from the healthy surrounding bone and grow through the material, eventually replacing the biomaterial. The body then slowly breaks down the biomaterial. Stem cells can also be added to the material, which grow into new bone and seek to connect to the body's own tissue. In this way, modern biomaterials put the body's own work much more into practice.
The materials with nanoparticles can be made and used in different ways. Sander: 'We make a paste of the various ingredients that we can inject into a hole, for example. But we also build up materials in a specific shape with a 3D printer. And sometimes material is malleable, or even elastic like a bouncy ball. The form chosen depends on the application.'
Finally, modern materials for filling bone are often biodegradable. 'We would like the body to replace the material itself as much as possible. It is important that we pay attention to the balance between the biodegradation rate of the material and the recovery of the body. If that is in balance, it ultimately provides a sustainable solution that lasts a lifetime.'
This article previously appeared in Radbode #3 2022.
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