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X-ray shows a filling in the front tooth

Health Science Center researchers use NASA technique to create new invisible cavity filler

May 2005

by Jacquelyn Spruce

Silver and gold, silver and gold.
Everyone wishes for silver and gold.

The late composer Johnny Marks was right when he wrote these famous holiday song lyrics. As a gift, silver and gold are stunning. But as cavity fillings, all that glitters shouldn’t shine, especially in your two front teeth. That’s why Health Science Center dental researchers have come up with something that’s literally "out of sight."

H. Ralph Rawls, Ph.D., professor in the department of restorative dentistry in the division of biomaterials at the Health Science Center, has spent more than eight years directing the Advanced Dental Restorative System program (ADRS). The program is directed at overcoming the deficiencies of current dental restorative composites and searching for a practical replacement for dental amalgam. The ADRS program is a joint effort between two divisions at the Southwest Research Institute (SwRI) and four departments within the Health Science Center. Together they hold a $5.9 million grant from the National Institute of Dental and Craniofacial Research.

Although amalgam, the most widely used material to fill a cavity, is efficient, it has a less appealing appearance and contains mercury, making it potentially harmful to the environment. Other composite materials are cosmetically appealing but do not last more than 10 years. They lack a strong enough resin to withstand strong chewing and tend to leave spaces between the filling and tooth, allowing room for further infection.

Dr. Rawls leads a research team that is working to develop an environmentally friendly, transparent, low-shrinking material to take the place of amalgam and other composite materials. He said it is imperative that the material shrinks very little, because otherwise gaps form between teeth and fillings, creating a magnet for tooth decay.

"We want this material to last much longer than current materials, making life easier for dentists and patients," said Benjamin Furman, a senior research associate with Dr. Rawls.

By collaborating with SwRI scientist Steve Wellinghoff, Ph.D., Dr. Rawls and his research team have earned eight patents since 2000 for innovative research on dental restoratives.

  Where's the filling?
You’d need X-ray vision to see that the woman in the photo has a filling in her front tooth. Thanks to UTHSC researchers, translucent cavity fillers are more effective and less expensive.

The most recent patent, received in June 2004, focuses on two major areas: 1.) developing a durable resin that undergoes low shrinkage and 2.) using nanometer-sized particles made of zirconium oxide to reinforce the resin. Since the resin is not adequate by itself, the tiny particles are added for reinforcement.

"It is analogous to the structure of a building," Dr. Rawls said. "A building cannot stand with concrete alone. Instead, metal rods serve to reinforce the concrete."

One of the team’s greatest challenges was finding a way to make the dental restorative optically translucent, yet visible on X-ray film.

"If the tooth filling material isn’t visible on an X-ray, dentists cannot see certain features needed to make diagnoses," Dr. Rawls said. "The smaller the reinforcing particles are in the resin, the more durable and translucent the material becomes. So over the years dental composites have been improved by continually reducing the size of the reinforcing particles. This was done by grinding them even finer, but grinding eventually reached its limit. That’s why we contacted Dr. Wellinghoff at the SwRI, to find a way to make extremely small particles that have all the properties needed."

Dr. Wellinghoff described a method he had used to create face shields and spacecraft windows for NASA using tantalum oxide, a limited, relatively expensive element that is similar to zirconium oxide. Tantalum oxide served as a reinforcing, transparent material in the face shields and windows.

"Astronauts experienced blinding flashes while in space because of the extreme cosmic rays," Furman said. "The cosmic rays are not noticeable on Earth because the Earth’s atmosphere blocks them. Dr. Wellinghoff discovered that if you add small enough particles to windows on the spacecrafts and face shields, they don’t interact with light but they filter out the cosmic rays."

Dr. Rawls and his team took Dr. Wellinghoff’s NASA technique and adapted it to their advantage. They used the tiny particles made up of zirconium oxide to create an adequate dental restorative as reinforcement in a low-shrinkage, liquid-crystal monomer. It is strong enough to last about 15 years and shrinks 25 percent to 50 percent less than current composite materials, greatly reducing the chance for leakage and decay. Dr. Rawls hopes it will be available for use in the next three to five years.

"We’re pleased to have had so much success through our collaborative effort with Dr. Wellinghoff and the others at SwRI," Dr. Rawls said. "But our study doesn’t end here. We learned that by using other zirconium compounds we will eventually be able to grow new types of nanometer-sized particles that actually arrange themselves so that they toughen a composite. We’re taking the things nature wants to do and using that to our advantage because it’s producing the materials we want."

Dr. Rawls’ research team is committed to growing these microscopic particles naturally as a physically attractive and more effective alternative to amalgam. The result will be reduced trips to the dentist, lower health costs and better oral hygiene.

What is a patent?

Patents ensure the 20-year right to exclude others from making, using or selling an invention. Throughout the 35 years the Dental School has been in existence, patents have contributed significant amounts of credibility to the school and its faculty and staff. Dr. Rawls currently has 10 patents. Seven are directly related to the dental restorative study. Below is a list of a few other inventions by Dental School faculty and staff who have been issued patents and have produced significant amounts of income for the Health Science Center.

  • "Radiograph Display System with Anatomical Icon for Selecting Digitized Stored Images" - Total income produced - $1,235,777.46

  • "Endodontic Instrument" - Total income produced - $413,214.62

  • "Shape-conforming Dental Wedges" - Total income produced - $58,000.00


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