A bad tooth can cause or create a lot of unrelated problems, a headache is included within that scope.
Yup, an infected tooth, if left untreated, can cause major problems, including brain damage and heart damage and death.
Yes, I have had headaches caused by toothaches. If I'm not mistaken, having a bad toothache can even make you nauseous. Toothaches are one of the worst types of pain I have experienced, so the headaches that come along with them are just torture.
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