Swollen submandibular gland one side. it is directly below a rotted molar and a very recently repaired cracked tooth ( needed a root canal but just filled it on the fly) could there be a connection with the teeth and this particular gland?

An abscess due to tooth infection in the same area may occur but a reactive lymph node is much more common. You will be much sicker, more pain and other constituent symptoms such as pain, high fever and chill if you have a tooth abscess which extends to the submandibular area.

Yes, there may be a connection.

Lymph glands act as a trap for pathogens such as bacteria and viruses. Yes, probably strong connection to your badly infected teeth. The lower you wait, the more serious the infection, the more spread to other organ systems. Please seek professional care.