Antibiotics take a bite out of bad gums.

Bleeding, receding gums may signal a serious disease that affects the roots of teeth and, if unchecked, can lead to tooth loss. To combat it, dentists scrape or plane away the root-level plaque and tartar caused by bacteria. In severe cases, oral surgeons make cuts at the gum line to improve access to affected roots-a procedure that can cost as much as $3,000.

Now, with treatments costing less than one-third of that, researchers at the University of Michigan School of Dentistry in Ann Arbor have successfully fought severe root-level bacterial infections with antibiotics, usually without surgery.

They treated 90 inner-city clinic patients who had advanced gum disease; in every case, other experienced periodontists had recommended surgery. After standard nonsurgical cleaning of tooth roots, all participants received drug capsules to be taken for 2 or 4 weeks, depending on the severity and extent of gum disease. The dentists followed up recalcitrant cases with as many as three rounds of topical antibiotics that they administered by temporarily gluing an experimental, drug-impregnated cellulose film to the root surface. Some patients received placebos during parts of the trial.

Using this antibiotic regimen, the researchers averted surgery or extraction for 690 of the 783 teeth initially deemed to need it. About 67 percent of the "hopeless teeth"-those identified by experienced specialists as being too far gone to save-no longer needed extraction or surgery, notes Walter J. Loesche, a leader of the study.

Overall, 81 percent of the patients avoided surgery, his team reports in the May Journal of Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology, and Endodontics. "And ones who still needed it required a greatly reduced amount," Loesche says.

He says that future studies will attempt to identify the most effective dose of antibiotics and work toward Food and Drug Administration approval for the drug-impregnated films used in the topical treatments.