Spend an afternoon listening to Tom Glass and the first thing you'll want to do afterward is rush out and buy a new toothbrush, or maybe two or three. The professor of forensic sciences, pathology, and dental medicine at the Oklahoma State University Center for Health Sciences has plenty to say about how toothbrushes are a breeding ground for viruses, bacteria, mould, and yeast, and consequently can easily transmit disease. The adjunct professor of microbiology advises healthy people to replace their toothbrush every two weeks and those with compromised immune systems to do so even more often. And no, he's not funded by manufacturers of the hygienic devices.

“Change your toothbrush on the 1st and 15th of every month. It's that simple,” Glass said in a lecture at the Pacific Dental Conference, which took place in Vancouver from March 8 to 10. His advice runs contrary to that of the American Dental Association, which recommends getting a new brush every three months.

“I called them [the ADA] and said ”˜Where do you get your science?' They had no science,” said Glass.

Besides maintaining a clinical practice, Glass has been researching the transmission of disease via tooth brushing for more than two decades. In one of his initial studies, published in a 1986 issue of Quintessence International, Glass cultured microorganisms taken from the toothbrushes of 10 healthy people and 10 people with periodontal disease. He also took cultures from five toothbrushes that were straight out of the package and had never been used. He found a wide array of growths on the brushes belonging to both groups of people, only the organisms were more concentrated on the brushes of those with disease. Among the microorganisms he found were Candida albicans, Staphylococcus epidermidis, and Clostridium ramosum. Plus, on four of the five brushes that hadn't been used, he found Staphylococcus epidermidis, a bacterium that isn't usually harmful to those in good health but that can cause infection in people with weakened immune systems.

Glass went on to look at where on toothbrushes contamination actually occurs. In a study published in Gerodontics the same year, he immersed brushes in Candida albicans and later found the microorganisms not just on the ends of the bristles but also on the head of the brush itself.

After establishing that both bacteria and yeast could survive on toothbrushes, Glass next examined the possibility of viral contamination. In a study he published in 1999 in Pathology, he used the herpes simplex virus type 1, which can cause recurring lip lesions and conjunctivitis, and can lead to encephalitis and pneumonia. The virus was still on the toothbrushes seven days after the initial contamination. He repeated the test using other viruses and came up with the same results.

Glass also cited two studies from the early '90s on the possibility of the transmission of HIV from one child to a sibling as a result of gingival bleeding and toothbrush sharing.

Brushing, Glass says, even when it's done carefully, can tear the tissues in the mouth. He studied the bristles on three brands of toothbrushes and found that although they were smooth and round to start with, they became sharp and jagged after two weeks of use. Hence his advice to replace your brush biweekly.

“The toothbrush scrapes the skin, and it's a reservoir for organisms,” he said.

What about disinfecting your toothbrush at home?

“Soaking used toothbrushes overnight in commercially available mouth rinses, cleaning disinfectants, hydrogen peroxide, or even alcoholic beverages was not an effective means of reducing the numbers of microorganisms,” Glass wrote in an article published in the September 2004 issue of Dentistry Today.

At the Vancouver conference, which drew nearly 11,000 attendees, Glass added that putting your brush in the dishwasher won't help either, though doing so will contaminate your plates. It takes about 10 minutes to sterilize a brush in a microwave, by which point the utensil itself will have melted.

Other advice? Don't store your toothbrush or floss in your bathroom. “The bathroom is really the outhouse,” said Glass, speaking with all the conviction of a preacher and noting that moisture from the shower provides the kind of environment in which germs thrive. “The bathroom is the most contaminated room in the house, and it's not the place to store intimate objects.”¦Every time you flush, what's going down is also coming up and contaminating everything in your bathroom. Get your toothbrush, toothpaste, and floss out of the bathroom and into the bedroom.”

He recommended having your own tube of toothpaste instead of sharing one.

If you bring your toothbrush to work, keep it in a sealed plastic bag, not in your desk drawer. Don't put a cap on it, since that creates a dark, warm, moist environment and “bugs just go wild.”

Drinking lots of water helps minimize the risk of infection in the mouth, Glass added. “One of your body's best defences against disease transmission is saliva,” he said. “If you don't have water you don't have saliva, and if you don't have saliva you don't have”¦immunoglobulins to ward off organisms.”

Don't brush your tongue, Glass stressed as he pointed to a projected image of a person's tongue with a toothbrush bristle embedded in it. “I call the tongue scraper ”˜the tongue destroyer',” he said. By brushing or scraping your tongue, “you will create all kinds of changes to the ecology of the tongue. You scrape off bodies of protection, called keratin. That's the body's protective mechanism” against germs.

You also don't need to spend big bucks on toothbrushes, according to Glass. The ones that cost $5 and above aren't any more effective than those priced at 87 cents.

Glass said to use a manual rather than a motorized brush, since the latter just helps spread bacteria and viruses. Look for the smallest brush, ideally clear instead of coloured, with the fewest number of bristles.

Change your toothbrush at the beginning and end of an illness, he said, since that will lessen the chance of reinfection.

And whatever you do, don't share.