In particular the medication that you may have taken for the pain (NAIDS like Ibuprofen) could increase the BP.
Jesus
An infected root is basically an abscess, and these can get nasty. It was one of the most common causes of death before such medications as antibiotics and indeed dentists. When the root dies, the pain disappears in many cases, so people are unaware of the underlying infection still existing in the root.
I agree with KK, I think the HBP was probably a result of the infection.
I wouldn't think hbp would cause a dental problem, but maybe the dental problem caused hpb due to the stress of the dental condition.