KU researchers work to increase durability of newer dental fillings

LAWRENCE — A team of researchers at the University of Kansas is hoping to curb tooth decay – while saving dental patients thousands of dollars – by working to improve the material used by dentists to fill cavities.

Distinguished Professor of Mechanical Engineering and Director of the Bioengineering Research Center Paulette Spencer and Associate Professor of Pharmaceutical Chemistry Jennifer Laurence received a $1.8 million, five-year grant from the National Institutes of Health to study enhancements to the polymer material used in fillings.

The two are leading a team of experts at KU’s Bioengineering Research Center to solve a problem that came about in the mid-1980s. Concerns about small amounts of mercury in the metal material that had been used to fill cavities for more than a hundred years led the dental industry to seek new options. Dentists switched to a plastic polymer filling that is safer, but less durable. The polymer lasts an average of 5.7 years compared with metal fillings that typically hold up for decades.

“Major problems with the plastics include a lack of resistance to the acid produced by bacteria present in the mouth, an inability to tolerate the wet environment, and surface features that attract the bacteria that lead to decay,” Spencer said. “The material tends to break down right at the point where it meets the tooth. The team’s research focuses on how salivary and microbial proteins interact and how to interfere with that interaction by engineering new polymers. “We are designing materials that would absorb the active part of that acid to neutralize it, preventing decay from starting in the first place,” Spencer said.

The durability issue with plastic fillings is especially problematic for those under age 10, who often lack the manual dexterity required to brush their teeth and have trouble sitting still, leaving the dentist to work on a moving target. Add in a lack of dental insurance – as of 2008, 4.6 million children did not obtain needed dental care because their families could not afford it – and the fact that a parent might be uncertain of a child’s dental needs, and it’s easy to see why an estimated 40 percent to 50 percent of those under age 10 have decay that’s untreated.

That leaves the parent in a tough spot if a child needs a filling at age two or three, Spencer said. The back teeth, where decay is most common, typically start coming in at about 12 months, and permanent teeth don’t replace these teeth until about age 9. With fillings failing at an average of 5.7 years, a parent could have to pay twice to have a filling put in the same tooth; one the child is going to lose anyway.

“The parent may opt to remove the tooth entirely, but the dentist still has to put in a brace, because the baby teeth serve as a guide post for the permanent teeth,” said Spencer, a licensed dentist with a doctorate in oral biology and physics and a master’s degree in materials engineering. “If we don’t have that, permanent teeth erupt without a guide. The permanent teeth will erupt in a manner that takes advantage of the available space, and this can leading to crowding and other problems. These problems may impact chewing, speech, and the child's smile.”

Spencer’s efforts to get to the root of the plastic polymer-filling problem would be stymied if she pursued a solution on her own. Research collaboration with experts from several disciplines is critical to finding unconventional solutions to engineering and scientific challenges, and is a key component of the research experience at KU’s Bioengineering Research Center. Laurence, with a pharmaceutical chemistry background, brings expertise on how proteins function, which plays a key role in breaking new ground in the research.

“We have two layers of defense in working to solve this problem. One is trying to minimize attachment of microbial proteins, which minimizes the overall damage to the tooth. The other is a buffer on the polymer material that serves as a defense against the acid generated by these microbes that destroy the tooth,” Laurence said.

More is at stake than just reducing a patient’s dental costs.

Studies show that in 2000, untreated tooth decay in children led to an estimated 50 million hours of school lost because of pain and discomfort, which most likely translated to parents missing a similar amount of hours from work. Laurence said when factoring in the pain, money and lost time associated with tooth decay, the research could have major benefits to all of mankind.

“This going to help almost every person on the planet,” Laurence said. “It’s really a quality of life issue at a very fundamental level.”