My 26-year old son, who has always had great teeth and takes good care of them, has needed 2 root canals in the last few months on lower teeth, and now says an upper tooth is giving him the same sort of problems. He's the first in our family to ever need a root canal. Do you think there could be some underlying medical problem that would suddenly cause his teeth to start having problems? He has been in good general health. Or is this a common thing?