In dentistry, gingival recession (receding gums) is the exposure in the roots of the teeth caused by a loss of gum tissue and/or retraction of the gingival margin from the crown of the teeth. Gum recession is a common problem in adults over the age of 40, but it may also occur starting from the teens. It may exist with or without concomitant decrease in crown-to-root ratio (recession of alveolar bone). Injections of stem cells have shown efficacy in stimulating growth of gum tissue.