FEATURE STORY — January/February 2009

Meet the TEETH

Dr. Thomas Diekwisch, director of Brodie Laboratory for Craniofacial Genetics, is investigating the molecular underpinnings of enamel. Such research may lead to enamel synthesis, which could help prevent cavities or address amelogenesis imperfecta, a disease that makes the tooth’s soft dentin layer particularly vulnerable to rampant decay.

Drs. Thomas Diekwisch and Anne George’s research on enamel and dentin at UIC’s College of Dentistry may extend the life of your pearly whites and unlock breakthroughs ranging from improved fillings to new ways of fighting breast cancer

 

By Sandra Swanson

Throughout our lifetime, we place a heavy workload on small chunks of highly mineralized tissue which encase a soft core of nerves and capillaries. Every time we smile, chew or talk, we depend on teeth—usually 32 of them, for the average adult. Aside from brushing and flossing, their presence generally goes unnoticed.

Our daily reliance on teeth is complicated, considering they present a minefield of potential problems. Despite diligent oral hygiene, they can still crack and decay—leading to cavities, infected root canals and loss of teeth entirely. Often those problems are accompanied by searing pain. If you’ve ever listened to the dentist’s drill and thought, “There must be a better way,” here’s some good news: Researchers at UIC’s College of Dentistry agree with you. And they’re doing something about it.

The Secrets of Tooth Formulation

Like the root below the gum line, the human tooth contains a wealth of information hidden from view. On the fourth floor of the College of Dentistry, researchers have begun to unlock secrets of tooth formation, and that knowledge could one day help revolutionize our experience in the dentist’s chair—including more effective ways to fill cavities or prevent them entirely. Their research may even lead to the creation of a human tooth. What’s more, these discoveries have potential implications far beyond dental health, ranging from bone fractures to breast cancer treatment.

To understand why teeth can be so problematic, consider the silent battle raging in your mouth. It’s filled with bacteria—some benign, some intent on wreaking dental havoc. As you enjoy, say, a slice of chocolate cake, so do the bacterial trouble-makers. They eat the sugar and produce acids that erode enamel—the fortress that covers the tooth above the gum line and protects softer tissues such as dentin and pulp underneath.

As the hardest, most mineralized substance in our bodies, enamel provides a strong defense against invaders, but it’s far from impenetrable. When the smallest flaw appears in enamel, bacteria enter and cause infection. This can result in a root-canal procedure or removal of the entire tooth.

To address those flaws, researchers are investigating enamel’s molecular underpinnings. It’s the focus of Dr. Thomas Diekwisch, director of Brodie Laboratory for Craniofacial Genetics. Broad-shouldered and 6’5”, Diekwisch easily fills the doorway to his office. He has reddish hair, a tidy moustache and beard, and a voice to match his stature—a resonant baritone, like Orson Welles with a German accent.

He underscores the importance of healthy enamel by sharing some worst-case scenarios, which have more dire consequences than a handful of cavities. “There is a congenital disease in which enamel is almost missing,” because the enamel-manufacturing proteins aren’t doing their job, explains Diekwisch. Called amelogenesis imperfecta, this disease makes the tooth’s soft dentin layer particularly vulnerable to rampant decay.

As a result, some patients “get crowns very early [in life] and they often get cavities all over the place. It [doesn’t] look very nice,” he says. “Many of the kids who grow up with amelogenesis imperfecta are suicidal, because they are afraid to open their mouth.”

It’s no surprise that when we sleep, one of our most common dreams involve losing teeth. Their importance transcends essential functions of chewing and pronunciation. “The aesthetics of your teeth have so much to do with your self-image,” says Diekwisch. “The more something takes away from the healthy tooth, the more your self-value—perceived or real—depreciates.”

Diekwisch’s work may help solve the problems created by defective mineralization. When some scientists share their enthusiasm for research, their speech quickens, as though they’re racing to the finish line of each sentence. This is not the case for Diekwisch. As his enthusiasm grows during a discussion, so does the space he leaves between words. Those pauses make a listener feel as though a mystery is unfolding. “I think the longer we immerse ourselves into this research, the more we realize how wonderful nature is—and complex,” he says.

Regenerating Enamel to Prevent Cavities

Complexity pervades the evolution of enamel. The insights gleaned from its developmental biology will yield important real-world applications. For instance, the more Diekwisch and his team learn how nature manufactures enamel, the more it helps them understand how to regenerate enamel. “You could use those [developmental biology] principles to re-mineralize human enamel,” says Diekwisch. That could help prevent cavities (and address dental congenital diseases) by strengthening the enamel fortress. One day, dentists may apply a coating to our teeth to help spur re-mineralization, he says.

Within the next several years, Diekwisch and his team may have the ability to create human enamel in a lab setting, taking researchers one step closer to creating an entire human tooth. But enamel synthesis will have other immediate benefits.

For example, synthesized enamel could provide a better alternative to current cavity-filling materials. Diekwisch speculates that a piece of synthesized enamel could be molded to fit the cavity. It wouldn’t be as stiff as porcellian inlays (which can cause cracks in teeth) nor as soft as amalgam (which abrades over time). In addition, it wouldn’t have the potentially toxic side effects associated with composite and amalgam fillings.

“The mechanical quality of human enamel hasn’t been surpassed by anything,” he explains. “It is extremely hard and extremely resilient.” As such, it holds promise beyond dental advances.

“We are trying to decipher the elements of enamel fabrication,” explains Diekwisch, “not only to replace aspects of human enamel, but also as a wonderful biomaterial for many other purposes.”

Diekwisch does have some specific purposes in mind, but remains tight-lipped for now, saying that the University isn’t ready to reveal details about such intellectual property. He does note that enamel’s fracture-resistant properties—and low cost—would make it ideal for certain consumer products. “Once we have figured ... how to make it, reproduction would be fairly inexpensive.”

To reach that point, however, requires more lab work. “We have not achieved enamel synthesis, but we have done experiments to understand the principles of enamel growth,” says Diekwisch.

Studying the evolutionary arc of enamel among species holds important clues for enamel synthesis. In his lab, Diekwisch has grown frog enamel on the teeth of mice. Now he’s repeating that process with cow enamel. In these experiments, Diekwisch is studying two extremes of enamel. Frog enamel breaks easily, while cows have some of the most resilient enamel in the animal kingdom (humans and mice fall somewhere in the middle). By analyzing the evolution of enamel resilience, Diekwisch hopes to uncover the function of enamel’s major protein, amelogenin.

Specifically, he wants to understand how amelogenin’s three main blocks of amino acids (commonly referred to as “domains”) work. “Once we [determine] the function of the individual domains, we believe we can then use this information to [assemble the] elements to grow enamel,” says Diekwisch.

Dr. Anne George and her researchers have made progress toward dentin regeneration in rats (above). They have also conducted research on regenerating a whole tooth. In one experiment last year, they grew mouse teeth underneath the top layer of a mouse’s kidney.

Dentin for Fillings

When it comes to regenerating dental tissue, Diekwisch isn’t alone at UIC. In another lab on the fourth floor, Dr. Anne George and her team have made critical discoveries about the production of dentin. This resilient layer of mineralized tissue provides a cushion underneath enamel and is destroyed when cavities form. Instead of filling cavities with artificial materials, such as polymers or resins, George wants to coax specific tooth cells to produce dentin. “It would be a much better way to fill the cavities,” she says.

Protein-mediated dentin regeneration would be biocompatible and non-toxic, unlike some filling material used today. While studies show that the trace amounts of mercury and other toxic substances in dental materials have no adverse health effects, George says those carcinogens aren’t exactly helping cells in the immediate vicinity.

But there’s a more pervasive problem with artificial materials: Even the best filling won’t provide a perfect fit. “Artificial materials don’t form a very good seal with existing dentin. So you always have bacteria seepage [which is] detrimental to the tooth,” she explains.

It doesn’t take much—even a nano-sized gap is large enough for foreign matter to infiltrate and destroy dentin, along with the rest of the tooth.

Prompting dentin production by using cells in the vicinity of the trauma, George hopes to solve that problem. If the cells make dentin to fill the cavities, “you [won’t] have any gaps,” says George.

Like cavity fillings, root-canal procedures are often stop-gap measures at best, and can lead to long-term problems. “Once you have a root canal, the dentist removes the pulp, fills the hole with calcium phosphate or similar material. So [the tooth is] dead,” says George. This creates complications, because the tooth no longer has the resilience to withstand activities such as chewing. “It cannot take all the mechanical forces … and so you have breakage at some point.”

George would like to revise the root-canal procedure by prompting cells to replace damaged tissue with natural dentin. This approach would keep the pulp in place and the tooth alive.

Her lab has already made progress toward dentin regeneration in rats. In one experiment, researchers opened a rodent’s root canal, and filled it with a scaffold—a collagenous matrix needed for dentin formation. Just as they aid the construction and repair of buildings, scaffolds inside our bodies provide temporary structures that allow cells to interact and grow.

Researchers also added stem cells to the mix. These cells have the ability to regenerate dentin. With a nudge in the right direction, stem cells can develop into specialized cells. This is achieved by adding a signaling molecule, which directs the stem cells into forming specialized dentin-making cells (called odontoblasts).

After three months, the hole in the rat’s tooth was completely filled with a mineralized tissue. However, “it’s hard to classify it as dentin,” remarks George. “We’re still working on it. We see ... that it can undergo mineralization, but what are the in-between mechanisms?”

It’s also a big step from rodent to human. George says it’s possible that a similar compound could be available in 10 years, as a method for filling a cavity or root canal. “We would certainly like to see this being used as a compound for various hard-tissue regeneration. But that is a long way off, because this is only the rat model.”

The Possibility of Cloned Teeth

George’s current field of research can be traced to her post-doctoral project at Northwestern University. The head of her lab, Dr. Arthur Veis, had identified a protein that was abundant in dentin. The protein’s genetic sequence was unknown, so George helped establish its DNA code, which was later named dentin matrix protein 2, or dentin phosphophoryn. Since then, she’s identified and cloned other dentin matrix proteins that play a role in dentin production (DMP1, DMP2, DMP3 and DMP4).

“Each one of them is fascinating,” relates George. For example, the signaling molecule used in the rodent root canal was DMP1. George thinks it can lead to a number of medical improvements for both future and existing technologies such as titanium dental implants.

Currently, these dental implants are surrounded by fibrous tissue when placed in the alveolar bone (jaw), which doesn’t provide a solid anchor. George wants to try a different approach—namely, coating the implant with a DMP1 peptide. The cells would make a mineralized matrix around the implant, grounding it into the socket, she explains. Consequently, the implant would behave like a pillar stuck in cement, instead of one surrounded by sand or mud.

One aspect of DMP1 that’s particularly intriguing to George: It doesn’t just show up in dentin. DMP1 also has been identified in bone, and in breast cancer and prostate cancer, where calcifications take place.

Although George’s lab isn’t studying cancer specifically right now, she says it’s an area of interest. Her ongoing research with proteins—and the role they play in mineralization—could have future implications for some cancer treatments. “Breast cancer cells … synthesize proteins such as DMP1, DMP2, which can bind calcium and phosphate and form these small mineralized nodules,” explains George. “If you know exactly how this mineralization process takes place, then you can create [cancer] therapies to target these proteins.”

Because DMP1 also plays an instrumental role in bone formation, George wants to explore the possibility of using a DMP1 compound to repair fractures and treat osteoporosis.

Her lab is also conducting research to regenerate a whole tooth. In one experiment last year, her research team dissected teeth from embryonic mice and separated two main cell types—epithelial and mesenchymal—which interact in tooth formation. They then recombined those two cell types in another mouse, and placed them just underneath the top layer of the animal’s kidney, a spot with a steady supply of nutrients. To show what happened next, George points to a photograph in the hallway outside her office, taken about 10 days after the procedure was performed. It’s a magnified view of tooth formation in a mouse’s kidney capsule and shows the formation of more than a dozen teeth.

Growing teeth this way in humans may be possible. “If you could take the cells and combine them, implant them under [human] skin (or where there is a supply of nutrients), you could grow a tooth, harvest it and put it back,” says George. “If you [could] develop similar ambient surroundings that can help it grow, that would be something.”

That’s a huge hurdle for science. But while we’re waiting for researchers to create brand-new pearly whites for us, the next few years will likely bring improved techniques for keeping the teeth we already have. And George will do her best to accelerate that process—after all, she has her own mouth to consider. “Personally, I’ve had two root canals,” says George, who grew up in India. “We didn’t have much preventive oral care back home.” Then she starts to laugh. “Every time I go to the dentist, I always feel like saying, ‘Can I just take some of my proteins and dump them in there?’”

According to George, the past several years of research have been focused on basic science, trying to understand molecular mechanisms. Now it’s time to parlay that into enhancements for our teeth and beyond. Says George: “The next 10 years will be focused on applications, so that humanity at large can reap the benefits of [us] knowing so much.”