Son's wisdom tooth nightmare

Three weeks ago my 24 year old son had 1 wisdom tooth removed due to persistent infection and soreness.  Two days after the extraction he developed a fever.  He called the dentist and the dentist told him he wasn't to concerned and to continue to take his antibiotics.  The next day my son could not swallow (not even his saliva, he had to spit it out in a cup), he couldn't talk and his neck was incredibly swollen.  I immediately took him to the hospital were they diagnosed his with a deep neck abscess.  The infection was blocking his airway, it was wrapping itself around the choroid artery and muscle.  Once the hospital had stabalized him, they operated on him at 10:00p.m.  and he was put into ICU on a respirator for 2 1/2 days and stayed in the hospital for additional 3 days after being released from ICU.   My question is... would the dentist have been able to see (visually or through Xray) that an infection was brewing in that tooth?  Did the bacteria get realeased during the surgery?   My son was very diligent in his hygiene before and following surgery and yet developed this life threatening infection.  It nearly cost my son his life.  My other concern is that he will have long lasting medical problems as a result.   

It isn't uncommon to devlop an infection following the removal of a tooth, so this might have been nothing to do with the previous infection.

I don't disagree, however, the severity of the infection was frightening.

How could it get so bad in such a short period of time.  I suppose we will never know.  One thing is for sure, my son is not interested in having anymore teeth removed. 

I found this and I'll post the link afterwards, it takes a little while to be approved

X-rays can show decay that may not normally be seen directly in the mouth, for example: under a filling, or between teeth. They can show whether you have an infection in the root of your tooth and how severe the infection is. 

http://www.dentalhealth.org/tell-me-about/topic/sundry/x-rays

I wasn't certain that infection shows on xrays but, apparently, it does