It's really hard to say when you are dealing with emergency vets and their findings. They do not know your dog, your dog's history or your feelings about your dog. They are there to assist you in emergency situations so they see the worst side of things. Unfortunatley, this can make them a little jaded and they will sometimes jump to the worst conclusions first.
That said -
The lymph nodes will swell any time there is an infection within the body. A root tooth issue is certainly a common cause of this.
I would not jump to any conclusions until you get to see the vet and have a fine needle aspiration. Be sure to do this tomorrow. Root tooth issues are one of the leading causes of heart disease in dogs because of the amount of bacteria that enters the bloodstream via the tooth issue.
Let me know if you want to discuss this more. And keep your chin up!
