A few pieces of medicated gum a day may keep the dentist away, at least for senior citizens.

Dental care is a particular problem among the elderly. Many take medications that decrease the production of saliva, which has natural antibiotic properties and helps wash away food debris. That leaves them more prone not only to cavities and mouth infections, but also to the accumulation of bacteria and yeast that can cause serious infections elsewhere, such as pneumonia.

Researchers studied 111 seniors living in 16 residential homes in West Hertfordshire, England. They split them into three groups. One group chewed gum with a combination of chlorhexidine acetate and xylitol (called ACHX in the study); another chewed xylitol gum; and the third group chewed nothing. Those who got either of the gums chewed one piece after breakfast and another after dinner.

Xylitol, a sweetener, plaque fighter, cavity fighter and saliva stimulator, was discovered in 1891 by the German chemist Emil Fischer and began to be used in the 1960s in the manufacture of foods, drugs and oral health products. Chlorhexidine acetate, which kills yeasts and bacteria, has been found to reduce plaque formation even more effectively than xylitol.

Dr. David Beighton and his colleagues from the Dental Caries Research Group at Guy's, King's and St. Thomas's Dental Institute in London, examined the groups for a year. They reported recently in the Journal of the American Geriatrics Society that both gums stimulated the flow of saliva, but that test subjects who got the xylitol gum or no gum had higher levels in their mouths of three microorganisms -- the mutans group of streptococci, which are most associated with tooth decay, lactobacilli and yeasts.

Both chewing gums reduced the amount of denture debris, sores around dentures, and cracks at the corners of the mouth, although the ACHX gum did it better.

Jane E. Allen is a reporter for the Los Angeles Times, a Tribune Publishing newspaper.