The Book of Odds points out that you are more likely to be injured by your toothbrush than by a garage door. (Who knew!)
The odds a person will visit an emergency department due to an accident involving a toothbrush in a year are 1 in 99,340, making a toothbrush slightly more dangerous on average than a garage door. (The odds a person will visit an emergency department due to an accident involving an automatic garage door in a year are 1 in 106,300)
The point of this post is that some people (read: crazies) will read something like this, panic, and elect to stop brushing their teeth altogether. But toothbrush risk must be looked at in the context of the alternative, not brushing your teeth. All risks must be analyzed this way before treatments are applied. (See my earlier post on the risks of getting the H1N1 shot vs. not getting the shot.)
According to the American Academy of Periodontology, there is a link between periodontal disease (a.k.a. gum disease caused by not brushing) and heart disease. So which risk has the greater impact and likelihood: cutting your gums while brushing your teeth (1:100,000) or getting arterial inflammation from the un-brushed bacteria from your mouth? (Data wasn’t provided for this risk but you get the idea.)
Finally, BookofOdds.com is a pretty (entertaining and) useful site which is one potentially useful tool for trying to approximate the measure some of your risks.