A dental infection can kill you.
But also true.
A toothache left untreated can, over time, develop an abscess. (An abscess is an infection that fills with pus and debris.)
Periodontal disease, left untreated, can also develop an abscess over time.
The trouble with many dental problems, though, is that in their early stages they are seldom painful.
In fact, sometimes, they aren't painful even after they become more advanced. So people tend to put off treating cavities and gum disease hoping it will just go away or get better on its own. Then, when it does get worse, they will often put that off as well. This is where it can get really dangerous.
One complication of a dental infection is called Ludwig's Angina. It's a type of infection that can travel from the roots of the teeth to the floor of the mouth and under the tongue. The infection can spread very quickly, creating a swelling that can block your airway or prevent you from swallowing. This can be life-threatening.
It can be cured with quick treatment that gets the ariway open and with antibiotics, but sometimes surgical intervention is also necessary.
The better solution is to never let your oral health become so neglected as to allow the possibility of this type of infection.