An infected tooth can go from painful to dangerous fast.

The idea that tooth decay can be life threatening may seem absurd at first, but there's evidence to suggest that what goes on inside your mouth may have far-reaching implications for your whole body health. For some time, scientists have been seeing a statistical correlation between poor oral health and heart disease. There are other statistical links, too, including associations between poor oral health and stroke, rheumatoid arthritis, some cancers, diabetes, respiratory infections and pregnancy problems [source: American Academy of Periodontology].
Research is ongoing to discover the way bacteria in the mouth can invade the body. Finding the link between oral hygiene and cardiovascular problems is right at the top of the list because people with periodontal disease (gum disease) have twice the risk of developing coronary artery disease 
There are a couple of theories that may explain why there's a link between heart disease and gum disease. In one, oral bacteria get into the bloodstream through sores in bleeding gums and attach themselves to the fatty plaques lining the blood vessels in the heart. Once there, they obstruct blood flow, which can lead to a heart attack. In another theory, arterial inflammation caused by periodontal bacteria restricts blood flow, eventually causing a heart attack.
In both scenarios, infections in the mouth can lead to a life-threatening condition -- in this case, involving the heart. As a side note, a 2007 paper published in "The New England Journal of Medicine" suggests that though the involvement of periodontal bacteria in heart attack and stroke may not be fully understood, a regimen of intensive periodontal treatment may reverse atherosclerosis, the buildup of fatty deposits inside arterial walls, and reduce cardiovascular risk [source: Perio.org].
Research into the reasons why poor oral health may be implicated in diseases and symptoms in other areas of the body is still ongoing. There does seem to be a solid link between tooth and gum health and whole body health, though. Has anyone ever died because he had poor brushing habits, tooth decay and gum disease? Although there's no definitive proof yet, there's support for the possibility that the mouth and body connection plays a much larger role in human health and wellness than we've suspected until now, including quality of life issues and longevity.