Researchers at the Medical College of Georgia have found that the cell damage caused by brushing your teeth may keep gums thicker and healthier, according to a study in the August issue of the Journal of Dental Research.
When toothbrush bristles tear holes in the epithelial cells that line the gums and tongue, growth factors that promote the growth of collagen, new blood cells, and blood vessels leak out of the damaged epithelial cells. This may make the gums thicker and healthier. The momentary rupture is patched up when calcium, abundant in saliva, moves into the cells and triggers internal membranes to move up.
An abstract of the original research can be found here.