Gums and resins.

Periodontal disease wears out most patients' patience and tolerance for pain--and it may indirectly soften their fillings as well, a new study suggests.

Where there's gum disease, there are inflammatory cells, including monocyte macrophages, which release a host of enzymes. One of those enzymes, cholesterol esterase, softens the polymers, or resins, used in dental work, Shiu Heman Tsang of the University of Toronto in Ontario reported last week at the American Association for Dental Research in San Antonio. Other studies suggest that a number of enzymes weaken dental polymers.

Tsang and his coworkers exposed three commonly used methacrylate polymers to buffer solutions both with and without cholesterol esterase for periods of 2 to 8 days. They used enzyme concentrations typical of what a filling sitting next to inflamed tissue would encounter. The researchers now plan to investigate how the enzyme softens the polymers.

Dentists often use polymer fillings because they can be made to match the color of teeth and have few known side effects. However, they fracture more easily than metallic fillings. Restorations wear out mainly because of chewing, but if they soften, they'll degrade more easily.

Scientists worry about the durability of dental polymers, in part because of the possibility--as yet undemonstrated--that toxic chemicals are released when the polymers degrade, says Tsang's research supervisor, J. Paul Santerre.