Drs Paul L. McNeil and Katsuya Miyake

Researchers have found that one way regular brushing may help keep gums firm and pink is, paradoxically, by tearing open cells. Bristles wielded with even gentle force tear holes in the epithelial cells that line the gums and tongue, causing a momentary rupture, researchers at the Medical College of Georgia (MCG) in Augusta (USA) report.

Epithelial cells (green) in the gum injured by brushing and resulting expression of c-fos (red)

Tearing enables calcium, abundant in saliva, to move into the cells, triggering internal membranes to move up and patch the hole, says Dr Katsuya Miyake, MCG cell biologist and the paper's co-first author. However, researchers say that in the seconds that repair takes, growth factors that promote growth of collagen, new cells and blood vessels leak out of injured cells.

Cell injury also turns on expression of the c-fos gene, an early-response gene often activated under stress that may be the first step in a response such as cell division or growth.

Dr Paul L. McNeil, MCG cell biologist and corresponding author explained, 'It is very clear that brushing your teeth is a healthy thing to do but we are thinking that there might be another positive aspect of brushing. Many tissues in our bodies respond to mechanical stress by adapting and getting stronger, like muscles. We think the gums may adapt to this mechanical stress by getting thicker and healthier. It is the no pain, no gain theory, the same as exercising.'

The research team, which also includes Dr Kaori Amano, a dental researcher at Kyorin University of Medicine in Japan, and Dr James L. Borke, MCG physiologist, injected a fluorescent dye into the blood stream that can only get into torn cells. They then brushed the teeth, gums and tongue of rats with a modified electric toothbrush. 'We saw lots of bright cells, and suggest that in addition to its well-known ability to remove bacteria and their harmful products from teeth, brushing may, by causing plasma membrane disruptions, lead to local cell-adaptive responses ultimately of benefit to gingival health.'

One immediate area of interest resulting from the research is to identify chemical signals produced by wounded oral cavity cells that could promote gum health. The method or type of brush might strongly influence the extent of epithelial cell-wounding and subsequent liberation of factors that promote gum health.

Researchers also found that brushing injures not only epithelial cells on the tongue's surface but muscle cells underneath as well. Dr McNeil continues, 'The mechanical forces must have been transmitted through the intact epithelium to the muscle cells which means our epithelium is tough and maintains a nice, resilient barrier but, not surprisingly, since it is not a hard surface, it transmits forces quite readily.'

The article Breaking biological barriers with a toothbrush appears in the Journal of Dental Research (2007; 86: 769–774).