Swedish researchers did a study with the miswak, also called the siwak and chewing stick. It is used for oral hygiene in several areas of the world, including Saudi Arabia, Sudan and Jordan.

Most miswaks come from the twigs or roots of the arak tree (Salvadora persica). It's also known as the toothbrush tree. But miswaks also can be made from other trees, including olive and walnut.

In the past, researchers tried to extract compounds from chewing sticks, but didn't find that they killed bacteria very well.

In this study, researchers used small pieces of miswak. Each piece weighed less than 1/100th of an ounce. They embedded some pieces in plastic lab dishes (Petri dishes) that were growing different kinds of mouth bacteria. They suspended some pieces above other Petri dishes.

Both strategies killed bacteria. The miswak pieces were best at killing two bacteria that cause periodontal disease. They also killed the bacteria that cause tooth decay, but to a lesser degree.

The pieces of miswak suspended above the Petri dishes were better at killing bacteria than the miswak pieces embedded in the dishes. The researchers suggest that the miswak might contain antibiotics that are given off as gases. This would explain how they could kill bacteria without touching them.

A miswak starts out several inches long. Each day, the tip is scraped and chewed until the fibers resemble bristles. The stick is then used like a toothbrush. After brushing, the stick is stored and placed in water overnight to soften it. The next day, the bristles are cut off and new ones are formed by chewing on the stick.

Men, particularly older men, are more likely than other people to use a miswak. Some people use both a plastic toothbrush and a miswak.

Other studies have found that miswaks remove plaque and kill bacteria in the mouth. In at least two studies, men who used miswaks had less plaque and healthier gums than men who used toothbrushes.

The study appears in the August issue of the Journal of Periodontology.