The University Record, April 10, 2000

IADR Research Presentations

Kids’ preferences in dentists, new approaches to growing bone, insights into childhood cavities are among topics faculty discussed at international meeting

By Nancy Ross-Flanigan
News and Information Services

From cellular processes to societal issues, U-M faculty discussed a wide range of dental research topics at the International Association for Dental Research meeting in Washington, D.C., April 5–8. Here are highlights of some of their presentations.

A new view of childhood cavities

According to conventional wisdom, very young children who get cavities in their front baby teeth—known as early childhood caries or baby bottle tooth decay—are much more likely to have dental problems in adulthood. The truth is a little more complicated, says Keith Heller, a research investigator in the School of Public Health.

“The fact that a child has nursing caries does not condemn him or her to a life of cavities, as some people have supposed,” Heller says. This type of decay develops when a child goes to sleep while nursing a bottle of milk, formula, fruit juice or other sweetened liquid. The liquids cling to the teeth overnight, and oral bacteria convert sugars in the liquids to acids, which attack the teeth. Once a child is weaned from the bottle, the source of the problem is gone, and the child is no more likely than others to develop future cavities. However, older children who get cavities in their back baby teeth are at higher risk for problems with their permanent teeth, Heller says, possibly because these caries develop as a result of poor dietary or oral hygiene habits that may continue in later life.

Heller and colleagues Amid Ismail of the School of Dentistry and Stephen Eklund, who has joint appointments in Public Health and Dentistry, used insurance claims data to track the development of cavities in 9,886 children between birth and 8 years. In spite of their findings about front teeth, “I wouldn’t want to say that parents shouldn’t be concerned about early childhood caries,” Heller cautions. “It’s absolutely important to care for the baby teeth, to prevent cavities and to treat decay properly if it does develop.” If the problem progresses too far, the child may need to be hospitalized and sedated for treatment.

Skin, bones and ‘reverse Jell-O’

A School of Dentistry team has produced bone from skin and gingiva (gum tissue) cells, an approach that could someday make bone grafts simpler to accomplish and far less painful for patients. Current methods require harvesting a patient’s bone marrow with a long needle or surgically removing a piece of bone, typically from the hip. With the new method, which is still in developmental stages, a tiny bit of skin or gum tissue is removed, cut into even smaller pieces and placed in a culture dish. The cultured cells are then engineered to secrete a protein, BMP-7, that induces bone formation. The engineered cells are seeded onto collagen sponges, which are placed in the area where bone repair is needed.

The team, which includes Prof. Bruce Rutherford, assistant Prof. Paul Krebsbach, research investigator Keni Gu and associate Prof. Renny Franceschi, tested the system on rats with large sections of bone missing from their skulls. New bone was produced, and the skulls were almost fully healed within just four weeks, “which was startling to me,” Rutherford says. The new bone looks just like naturally-produced bone, with a hard outer coating, a spongy interior and a marrow core. The researchers plan more experiments to determine whether it functions like natural bone. They also are experimenting with using a hydrogel—a material that changes from liquid to gel under certain conditions—instead of the collagen sponges. The particular hydrogel they use acts like “reverse Jell-O,” remaining liquid when cool and firming up when warm. Injected as liquid into a lesion of any size or shape, the material gels as it warms to body temperature, holding the engineered cells in the appropriate place.

Kids show early preferences

Children as young as 4 years of age show distinct preferences in the gender of their dentist or physician, with boys preferring males and girls preferring females, a School of Dentistry study finds. When it comes to race, however, the picture is not as clear-cut. In the study, children ages 4–8 were shown photographs of African American, Asian American and European American men and women and asked which they would want as their dentist or medical doctor and which they would not want. European American children preferred dentists of their own ethnicity, but show no such preference for medical doctors. African American children preferred African American dentists, but wanted their medical doctor to be an ethnicity other than their own.

While the reasons for the children’s choices are perplexing, the results point to the need to teach children that dentists and medical doctors can be male or female and can belong to any ethnic group, the authors say. The study was the graduate thesis of Erin Redwine, who now practices pediatric dentistry in Flint. Redwine’s collaborators on the project were associate Prof. Marita Inglehart, associate Prof. Marilyn Woolfolk, adjunct assistant Prof. Daniel Briskie and Prof. Robert Feigal.

Air abrasion effective for small cavities

Tiny cavities are a dilemma for dentists. There’s a limit to how small the bur on a dental drill can be, so drilling out a miniscule area of decay with even the smallest bur will likely destroy some perfectly good tooth structure. And sometimes an area that has just begun to decay will remineralize, stopping or reversing the decay process. “So little cavities may just go away or at least not get any bigger,” explains James Hamilton, clinical assistant professor of dentistry. Many dentists have begun treating tiny cavities with air abrasion, a relatively painless process that uses compressed air to shoot tiny abrasive particles at the tooth surface, but until now, the technique’s effectiveness had not been thoroughly evaluated, Hamilton says. In a randomized, controlled clinical study conducted by Hamilton, dentistry Prof. Joseph Dennison and clinical assistant Prof. Kenneth Stoffers, the method appeared to prevent small cavities from developing into bigger ones. The researchers expected about 25 percent of small cavities to become larger within one year, but in patients treated with air abrasion, only 5 percent to 10 percent did. The researchers now plan to follow groups of patients for two to three years and to try to find ways of predicting which small cavities are likely to get bigger.

A science fiction fix

A scene in the movie Face/Off shows a laser-based machine manufacturing a human ear. That’s science fiction, but real-life researchers are working on a similar process. The idea is to use a patient’s own CT scan or MRI image to custom-build a replacement joint or repair a skeletal defect, says Scott Hollister, an associate professor with joint appointments in the College of Engineering and the Medical School. Hollister is collaborating on the project with Stephen Feinberg, associate professor of dentistry and of surgery; Paul Krebsbach, assistant professor of dentistry; John Halloran, professor of materials science and engineering; Tien Min Chu, post-doctoral fellow in materials science and engineering; and Juan Taboas, doctoral student in biomedical engineering.

From the CT or MRI image, Hollister creates a computer file of data describing the size and shape of the structure to be replaced. A computer-aided manufacturing machine can then use the data to create the structure from polymers or other materials. Instead of creating the structure directly, however, the researchers typically use the machine to make its inverse, which they use as a mold. The actual structure is cast from a biopolymer or a bioceramic and seeded with cells or growth factors. When implanted into the appropriate part of the body, the structure acts as a scaffold on which new bone can grow, eventually taking the shape of the scaffold. The researchers also use microscopic CT images of bone to make the interior of the scaffold resemble real bone, a feature that encourages new bone growth. The team has tested parts of the system in animals and soon plans to use it to reconstruct the temporomandibular joint in pigs. In humans, the temporomandibular joint is susceptible to damage from arthritis, and current approaches to treating the problem are “not totally satisfactory,” Hollister says.

Minorities: Desire for healthy teeth doesn’t match reality

National health statistics show that minority children have poorer oral health than white children, but the reasons for the disparity have been unclear. While some research has documented differences due to lack of access to dental services, less attention has been paid to psychosocial factors, such as oral health habits, the value placed on healthy teeth, and knowledge of preventive measures, such as sealants. To explore these factors, a School of Dentistry team surveyed 203 Hispanic migrant worker children in Northern Michigan and 50 African American parents in a Western Michigan inner city dental practice. While 90 percent of the children and parents said that good oral health was important to them, their oral health habits and knowledge of preventive measures were poor. Fifteen percent of the migrant worker children did not own a toothbrush, and 57 percent had no dental floss at home. One out of five children had never seen a dentist before coming to clinics operated by the School of Dentistry. Not surprisingly, many of the children had dental problems, such as toothaches and difficulty chewing. “It is obvious that parents and children from disadvantaged minority groups have a strong desire for good oral health, but need professional support to be able to achieve it,” concluded the authors, dentistry student Damon Watson, associate Prof. Marita Inglehart and Prof. Robert Bagramian.

Diagnosing periodontal disease

The effects of periodontal disease are unmistakable—receding gums and, in severe cases, breakdown of bone. But it’s not so easy to tell whether the disease is still active or whether treatment measures have stopped it in its tracks. Assistant professor of dentistry William Giannobile and colleagues at the U-M and the State University of New York are working to develop a simple test for active periodontal disease that could be done in a dentist’s office. The researchers have found that levels of a protein called ICTP are a good indicator of active periodontal disease. This protein, which is released when bone breaks down, also is found in the blood of patients with osteoporosis and bone cancer. In a recent study of 70 patients with periodontal disease, Giannobile’s group found that ICTP levels declined after successful treatment, which suggests that measuring ICTP levels could be a useful way to monitor the disease. Currently, tests for ICTP must be performed in a laboratory, but the researchers are working with a Long Island company, BioMimetic Pharmaceuticals Inc., to develop a simpler, chair-side test.